FRB 20220912A is a repeating Fast Radio Burst (FRB) that was discovered in Fall 2022 and remained highly active for several
months. We report the detection of 35 FRBs from 541 hours of follow-up observations of this source using the recently refurbished
Allen Telescope Array, covering 1344 MHz of bandwidth primarily centered at 1572 MHz. All 35 FRBs were detected in the
lower half of the band with non-detections in the upper half and covered fluences from 4–431 Jy-ms (median=48.27 Jy-ms). We
find consistency with previous repeater studies for a range of spectrotemporal features including: bursts with downward frequency
drifting over time; a positive correlation between bandwidth and center frequency; and a decrease in sub-burst duration over
time. We report an apparent decrease in the center frequency of observed bursts over the 2 months of the observing campaign
(corresponding to a drop of 6.21 ± 0.76 MHz per day). We predict a cut-off fluence for FRB 20220912A of 𝐹max ≲ 104
Jy-ms,
for this source to be consistent with the all-sky rate, and find that FRB 20220912A significantly contributed to the all-sky
FRB rate at a level of a few percent for fluences of ∼100 Jy-ms. Finally, we investigate characteristic timescales and sub-burst
periodicities and find a) a median inter-subburst timescale of 5.82±1.16 ms in the multi-component bursts and b) no evidence of
strict periodicity even in the most evenly-spaced multi-component burst in the sample. Our results demonstrate the importance
of wideband observations of FRBs, and provide an important set of observational parameters against which to compare FRB
progenitor and emission mechanism models
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
Fast radio bursts trigger aftershocks resembling earthquakes, but not solar f...Sérgio Sacani
The production mechanism of repeating fast radio bursts (FRBs) is still a mystery, and correlations between burst occurrence
times and energies may provide important clues to elucidate it. While time correlation studies of FRBs have been mainly
performed using wait time distributions, here we report the results of a correlation function analysis of repeating FRBs in the
2D space of time and energy. We analyse nearly 7,000 bursts reported in the literature for the three most active sources of
FRB 20121102A, 20201124A, and 20220912A, and find the following characteristics that are universal in the three sources. A
clear power-law signal of the correlation function is seen, extending to the typical burst duration (∼ 10 msec) towards shorter
time intervals (t). The correlation function indicates that every single burst has about a 10–60 per cent chance of producing
an aftershock at a rate decaying by a power law as ∝ (t)
−p with p = 1.5–2.5, like the Omori–Utsu law of earthquakes. The
correlated aftershock rate is stable regardless of source activity changes, and there is no correlation between emitted energy
and t. We demonstrate that all these properties are quantitatively common to earthquakes, but different from solar flares in
many aspects, by applying the same analysis method for the data on these phenomena. These results suggest that repeater FRBs
are a phenomenon in which energy stored in rigid neutron star crusts is released by seismic activity. This may provide a new
opportunity for future studies to explore the physical properties of the neutron star crust.
The document analyzes the merger fractions of radio-loud and radio-quiet active galactic nuclei (AGN) at z > 1 using new Hubble Space Telescope (HST) samples. It finds that 92% (+8%/-14%) of radio-loud galaxies at z > 1 show evidence of recent or ongoing mergers, while only 38% (+16%/-15%) of matched radio-quiet samples exhibit mergers. This provides strong evidence that mergers are the triggering mechanism for radio-loud AGN phenomena like relativistic jet launching, and that major black hole mergers may spin up central supermassive black holes in these objects.
Galaxy interactions are the dominant trigger for local type 2 quasarsSérgio Sacani
The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with
some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we
present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected
type 2 quasars – the QSOFEED sample (L[O III] > 108.5 L; z < 0.14). Based on visual inspection by eight classifiers, we find
clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with
65+6
−7 per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared
with only 22+5
−4 per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The
type 2 quasar hosts are a factor of 3.0+0.5 −0.8 more likely to be morphologically disturbed than their matched non-AGN counterparts,
similar to our previous results for powerful 3CR radio AGN of comparable [O III] emission-line luminosity and redshift. In
contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become
visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the
pre-coalescence phase (61+8
−9 per cent). We argue that much of the apparent ambiguity that surrounds observational results in this
field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological
surface brightness dimming.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
Fast radio bursts trigger aftershocks resembling earthquakes, but not solar f...Sérgio Sacani
The production mechanism of repeating fast radio bursts (FRBs) is still a mystery, and correlations between burst occurrence
times and energies may provide important clues to elucidate it. While time correlation studies of FRBs have been mainly
performed using wait time distributions, here we report the results of a correlation function analysis of repeating FRBs in the
2D space of time and energy. We analyse nearly 7,000 bursts reported in the literature for the three most active sources of
FRB 20121102A, 20201124A, and 20220912A, and find the following characteristics that are universal in the three sources. A
clear power-law signal of the correlation function is seen, extending to the typical burst duration (∼ 10 msec) towards shorter
time intervals (t). The correlation function indicates that every single burst has about a 10–60 per cent chance of producing
an aftershock at a rate decaying by a power law as ∝ (t)
−p with p = 1.5–2.5, like the Omori–Utsu law of earthquakes. The
correlated aftershock rate is stable regardless of source activity changes, and there is no correlation between emitted energy
and t. We demonstrate that all these properties are quantitatively common to earthquakes, but different from solar flares in
many aspects, by applying the same analysis method for the data on these phenomena. These results suggest that repeater FRBs
are a phenomenon in which energy stored in rigid neutron star crusts is released by seismic activity. This may provide a new
opportunity for future studies to explore the physical properties of the neutron star crust.
The document analyzes the merger fractions of radio-loud and radio-quiet active galactic nuclei (AGN) at z > 1 using new Hubble Space Telescope (HST) samples. It finds that 92% (+8%/-14%) of radio-loud galaxies at z > 1 show evidence of recent or ongoing mergers, while only 38% (+16%/-15%) of matched radio-quiet samples exhibit mergers. This provides strong evidence that mergers are the triggering mechanism for radio-loud AGN phenomena like relativistic jet launching, and that major black hole mergers may spin up central supermassive black holes in these objects.
Galaxy interactions are the dominant trigger for local type 2 quasarsSérgio Sacani
The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with
some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we
present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected
type 2 quasars – the QSOFEED sample (L[O III] > 108.5 L; z < 0.14). Based on visual inspection by eight classifiers, we find
clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with
65+6
−7 per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared
with only 22+5
−4 per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The
type 2 quasar hosts are a factor of 3.0+0.5 −0.8 more likely to be morphologically disturbed than their matched non-AGN counterparts,
similar to our previous results for powerful 3CR radio AGN of comparable [O III] emission-line luminosity and redshift. In
contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become
visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the
pre-coalescence phase (61+8
−9 per cent). We argue that much of the apparent ambiguity that surrounds observational results in this
field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological
surface brightness dimming.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar ...Sérgio Sacani
Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs
modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial
correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using
observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which
spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise
process. Represented as a strain spectrum h Af c 1yr = -1 a ( ) , we measure A 3.1 10 0.9 = ´ 1.3 15 -
+ - and
α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3,
corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we
recover an amplitude of A 2.04 10 0.22 = ´ 0.25 15 -
+ - . However, we demonstrate that the apparent signal strength is timedependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred
common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by
hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing
pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB,
with an estimated false-alarm probability of p 0.02 (approx. 2σ). The long timing baselines of the PPTA and the
access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
This document summarizes observations of the lensed galaxy HATLAS J142935.3-002836 (H1429-0028) from the Herschel-ATLAS survey. Optical spectroscopy revealed the foreground lens is at redshift 0.218, while the background galaxy is at redshift 1.027. High-resolution imaging from Hubble Space Telescope and Keck adaptive optics show the background galaxy is comprised of two components and a tidal tail, resembling a major merger. Analysis of ALMA observations of CO emission provides a dynamical mass estimate of one component as 5.8 ± 1.7 × 1010 M☉. Modeling of the spectral energy distribution indicates the total stellar mass is 1.32
Exploring Proxies for the Supermassive Black Hole Mass Function: Implications...Sérgio Sacani
Supermassive black holes (SMBHs) reside at the center of every massive galaxy in the local universe with masses
that closely correlate with observations of their host galaxy, implying a connected evolutionary history. The
population of binary SMBHs, which form following galaxy mergers, is expected to produce a gravitational-wave
background (GWB) detectable by pulsar timing arrays (PTAs). PTAs are starting to see hints of what may be a
GWB, and the amplitude of the emerging signal is toward the higher end of model predictions. Simulated
populations of binary SMBHs can be constructed from observations of galaxies and are used to make predictions
about the nature of the GWB. The greatest source of uncertainty in these observation-based models comes from the
inference of the SMBH mass function, which is derived from observed host galaxy properties. In this paper, I
undertake a new approach for inferring the SMBH mass function, starting from a velocity dispersion function
rather than a galaxy stellar mass function. I argue that this method allows for a more direct inference by relying on
a larger suite of individual galaxy observations as well as relying on a more “fundamental” SMBH mass relation. I
find that the resulting binary SMBH population contains more massive systems at higher redshifts than previous
models. Additionally, I explore the implications for the detection of individually resolvable sources in PTA data.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
What determines the_density_structure_of_molecular_cloudsSérgio Sacani
This document analyzes column density probability distribution functions (PDFs) derived from Herschel observations of the Orion B, Aquila, and Polaris molecular clouds to understand what physical processes influence the density structure. The PDFs of Orion B and Aquila show a lognormal distribution at low densities transitioning to a power-law tail at high densities, indicating gravitational collapse. The Orion B PDF is broader, likely due to external compression. The quiescent Polaris subregion PDF is nearly lognormal, suggesting turbulence governs its density, while a filament subregion shows excess density above a visual extinction of 1, possibly from physical processes like magnetic fields. The document concludes that turbulence, gravity, collapse, and external compression
Ещё шесть радиосигналов неизвестной природы получены из-за пределов нашей гал...Anatol Alizar
This document reports on radio and X-ray observations of FRB 121102, the only known repeating fast radio burst source. Six additional radio bursts from FRB 121102 were detected - five with the Green Bank Telescope at 2 GHz and one with the Arecibo Observatory at 1.4 GHz, bringing the total detected bursts from this source to 17. X-ray observations from Swift and Chandra show at least one possible counterpart, but the probability of chance superposition is high. Radio imaging with the VLA places an upper limit on any continuum emission at the location. The repeating nature of FRB 121102 indicates that at least some FRBs originate from a repeating phenomenon and not a cataclysmic event.
The dispersion–brightness relation for fast radio bursts from a wide-field su...Sérgio Sacani
Despite considerable efforts over the past decade, only 34 fast radio
bursts—intense bursts of radio emission from beyond our Galaxy—
have been reported1,2
. Attempts to understand the population as a
whole have been hindered by the highly heterogeneous nature of the
searches, which have been conducted with telescopes of different
sensitivities, at a range of radio frequencies, and in environments
corrupted by different levels of radio-frequency interference
from human activity. Searches have been further complicated by
uncertain burst positions and brightnesses—a consequence of the
transient nature of the sources and the poor angular resolution of
the detecting instruments. The discovery of repeating bursts from
one source3
, and its subsequent localization4
to a dwarf galaxy at a
distance of 3.7 billion light years, confirmed that the population
of fast radio bursts is located at cosmological distances. However,
the nature of the emission remains elusive. Here we report a well
controlled, wide-field radio survey for these bursts. We found 20,
none of which repeated during follow-up observations between
185–1,097 hours after the initial detections. The sample includes
both the nearest and the most energetic bursts detected so far. The
survey demonstrates that there is a relationship between burst
dispersion and brightness and that the high-fluence bursts are
the nearby analogues of the more distant events found in highersensitivity,
narrower-field surveys5
.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
1) Pulsar timing arrays are searching for gravitational waves from massive black hole binaries in the nanohertz frequency range.
2) Current pulsar timing array efforts have not detected a gravitational wave signal but are placing increasingly stringent upper limits.
3) Future and more sensitive radio telescopes like FAST, MeerKAT, and the Square Kilometre Array will improve the prospects for a direct detection of gravitational waves from massive black hole binaries within the next decade.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
This document analyzes the position angle (PA) distribution of filaments observed in radio images of the Galactic center, obtained using the MeerKAT radio telescope. It finds that short filaments (<66") have PAs concentrated along the Galactic plane (60-120 degrees), pointing radially towards the supermassive black hole Sgr A*. This suggests the filaments have been aligned by a collimated outflow from Sgr A* extending along the Galactic plane. The outflow pressure is estimated to require an outflow rate of 10^-4 solar masses per year over ~6 million years to align the filaments. Longer filaments (>66") show a broader PA distribution, with a peak around -3 degrees
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624Sérgio Sacani
This document summarizes evidence for an intermediate-mass black hole located at the center of the globular cluster NGC 6624. The authors present over 25 years of timing observations of the millisecond pulsar PSR B1820-30A, which is located very close to the cluster center. Modeling of the higher order rotational frequency derivatives reveals that the pulsar is likely in a high-eccentricity orbit around a massive companion with a mass greater than 7500 solar masses located at the cluster center, which would be an intermediate-mass black hole. Additional evidence from modeling the cluster gravitational potential and dynamics supports the presence of a central black hole with a minimum mass of around 60,000 solar masses. The observations of this
A Simultaneous dual-site technosignature search using international LOFAR sta...Sérgio Sacani
The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
The abundance of_x_shpoaed_radio_sources_implications_for_the_gravitational_w...Sérgio Sacani
Devem existir menos buracos negros supermassivos binários nos núcleos das galáxias do que se pensava anteriormente, disse uma equipe de cientistas da Universidade de Brandeis em Waltaham, Massachussets, e do Instituto de Pesquisa Raman em Bangalore, na Índia.
A maior parte das galáxias massivas no universo devem abrigar no mínimo um buraco negro supermassivo em seus núcleos.
Quando duas galáxias colidem, seus buracos negros se juntam, formando uma dança colossal que resulta numa combinação de par. Esse processo é a mais intensa fonte de ondas gravitacionais no universo, que ainda precisam ser diretamente detectadas.
“As ondas gravitacionais representam a próxima fronteira da astrofísica, e sua detecção levará a novas ideias sobre o universo. É importante se ter a maior quantidade de informação possível sobre as fontes dessas ondas”, disse o Dr. David Roberts, um membro da equipe da Universidade de Brandeis.
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
This document summarizes an X-ray study of the supernova remnant G352.7-0.1 using data from XMM-Newton and Chandra observations. Prior observations revealed G352.7-0.1 has a shell-like radio morphology but center-filled thermal X-ray morphology, classifying it as a mixed-morphology supernova remnant. The new observations confirm the X-ray emission comes from the interior and is dominated by ejecta. Spectra from XMM-Newton are fit by a single thermal component with enhanced silicon and sulfur. Some Chandra spectra require a second thermal component to fit, with solar abundances providing a better physical model. No evidence of overionization was found. A neutron
Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Cons...Sérgio Sacani
Many recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the
anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a
constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space
Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitationalwave Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies
of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact
binaries, and a recently proposed scenario for massive black hole seed formation through multiple mergers of
stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost
unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through crosscorrelation with the cosmic microwave background (CMB) fluctuations. In particular, we find that a constellation
of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing
convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECI
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
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Ähnlich wie Characterization of the Repeating FRB 20220912A with the Allen Telescope Array
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar ...Sérgio Sacani
Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs
modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial
correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using
observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which
spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise
process. Represented as a strain spectrum h Af c 1yr = -1 a ( ) , we measure A 3.1 10 0.9 = ´ 1.3 15 -
+ - and
α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3,
corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we
recover an amplitude of A 2.04 10 0.22 = ´ 0.25 15 -
+ - . However, we demonstrate that the apparent signal strength is timedependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred
common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by
hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing
pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB,
with an estimated false-alarm probability of p 0.02 (approx. 2σ). The long timing baselines of the PPTA and the
access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
This document summarizes observations of the lensed galaxy HATLAS J142935.3-002836 (H1429-0028) from the Herschel-ATLAS survey. Optical spectroscopy revealed the foreground lens is at redshift 0.218, while the background galaxy is at redshift 1.027. High-resolution imaging from Hubble Space Telescope and Keck adaptive optics show the background galaxy is comprised of two components and a tidal tail, resembling a major merger. Analysis of ALMA observations of CO emission provides a dynamical mass estimate of one component as 5.8 ± 1.7 × 1010 M☉. Modeling of the spectral energy distribution indicates the total stellar mass is 1.32
Exploring Proxies for the Supermassive Black Hole Mass Function: Implications...Sérgio Sacani
Supermassive black holes (SMBHs) reside at the center of every massive galaxy in the local universe with masses
that closely correlate with observations of their host galaxy, implying a connected evolutionary history. The
population of binary SMBHs, which form following galaxy mergers, is expected to produce a gravitational-wave
background (GWB) detectable by pulsar timing arrays (PTAs). PTAs are starting to see hints of what may be a
GWB, and the amplitude of the emerging signal is toward the higher end of model predictions. Simulated
populations of binary SMBHs can be constructed from observations of galaxies and are used to make predictions
about the nature of the GWB. The greatest source of uncertainty in these observation-based models comes from the
inference of the SMBH mass function, which is derived from observed host galaxy properties. In this paper, I
undertake a new approach for inferring the SMBH mass function, starting from a velocity dispersion function
rather than a galaxy stellar mass function. I argue that this method allows for a more direct inference by relying on
a larger suite of individual galaxy observations as well as relying on a more “fundamental” SMBH mass relation. I
find that the resulting binary SMBH population contains more massive systems at higher redshifts than previous
models. Additionally, I explore the implications for the detection of individually resolvable sources in PTA data.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
What determines the_density_structure_of_molecular_cloudsSérgio Sacani
This document analyzes column density probability distribution functions (PDFs) derived from Herschel observations of the Orion B, Aquila, and Polaris molecular clouds to understand what physical processes influence the density structure. The PDFs of Orion B and Aquila show a lognormal distribution at low densities transitioning to a power-law tail at high densities, indicating gravitational collapse. The Orion B PDF is broader, likely due to external compression. The quiescent Polaris subregion PDF is nearly lognormal, suggesting turbulence governs its density, while a filament subregion shows excess density above a visual extinction of 1, possibly from physical processes like magnetic fields. The document concludes that turbulence, gravity, collapse, and external compression
Ещё шесть радиосигналов неизвестной природы получены из-за пределов нашей гал...Anatol Alizar
This document reports on radio and X-ray observations of FRB 121102, the only known repeating fast radio burst source. Six additional radio bursts from FRB 121102 were detected - five with the Green Bank Telescope at 2 GHz and one with the Arecibo Observatory at 1.4 GHz, bringing the total detected bursts from this source to 17. X-ray observations from Swift and Chandra show at least one possible counterpart, but the probability of chance superposition is high. Radio imaging with the VLA places an upper limit on any continuum emission at the location. The repeating nature of FRB 121102 indicates that at least some FRBs originate from a repeating phenomenon and not a cataclysmic event.
The dispersion–brightness relation for fast radio bursts from a wide-field su...Sérgio Sacani
Despite considerable efforts over the past decade, only 34 fast radio
bursts—intense bursts of radio emission from beyond our Galaxy—
have been reported1,2
. Attempts to understand the population as a
whole have been hindered by the highly heterogeneous nature of the
searches, which have been conducted with telescopes of different
sensitivities, at a range of radio frequencies, and in environments
corrupted by different levels of radio-frequency interference
from human activity. Searches have been further complicated by
uncertain burst positions and brightnesses—a consequence of the
transient nature of the sources and the poor angular resolution of
the detecting instruments. The discovery of repeating bursts from
one source3
, and its subsequent localization4
to a dwarf galaxy at a
distance of 3.7 billion light years, confirmed that the population
of fast radio bursts is located at cosmological distances. However,
the nature of the emission remains elusive. Here we report a well
controlled, wide-field radio survey for these bursts. We found 20,
none of which repeated during follow-up observations between
185–1,097 hours after the initial detections. The sample includes
both the nearest and the most energetic bursts detected so far. The
survey demonstrates that there is a relationship between burst
dispersion and brightness and that the high-fluence bursts are
the nearby analogues of the more distant events found in highersensitivity,
narrower-field surveys5
.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
1) Pulsar timing arrays are searching for gravitational waves from massive black hole binaries in the nanohertz frequency range.
2) Current pulsar timing array efforts have not detected a gravitational wave signal but are placing increasingly stringent upper limits.
3) Future and more sensitive radio telescopes like FAST, MeerKAT, and the Square Kilometre Array will improve the prospects for a direct detection of gravitational waves from massive black hole binaries within the next decade.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
This document analyzes the position angle (PA) distribution of filaments observed in radio images of the Galactic center, obtained using the MeerKAT radio telescope. It finds that short filaments (<66") have PAs concentrated along the Galactic plane (60-120 degrees), pointing radially towards the supermassive black hole Sgr A*. This suggests the filaments have been aligned by a collimated outflow from Sgr A* extending along the Galactic plane. The outflow pressure is estimated to require an outflow rate of 10^-4 solar masses per year over ~6 million years to align the filaments. Longer filaments (>66") show a broader PA distribution, with a peak around -3 degrees
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624Sérgio Sacani
This document summarizes evidence for an intermediate-mass black hole located at the center of the globular cluster NGC 6624. The authors present over 25 years of timing observations of the millisecond pulsar PSR B1820-30A, which is located very close to the cluster center. Modeling of the higher order rotational frequency derivatives reveals that the pulsar is likely in a high-eccentricity orbit around a massive companion with a mass greater than 7500 solar masses located at the cluster center, which would be an intermediate-mass black hole. Additional evidence from modeling the cluster gravitational potential and dynamics supports the presence of a central black hole with a minimum mass of around 60,000 solar masses. The observations of this
A Simultaneous dual-site technosignature search using international LOFAR sta...Sérgio Sacani
The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
The abundance of_x_shpoaed_radio_sources_implications_for_the_gravitational_w...Sérgio Sacani
Devem existir menos buracos negros supermassivos binários nos núcleos das galáxias do que se pensava anteriormente, disse uma equipe de cientistas da Universidade de Brandeis em Waltaham, Massachussets, e do Instituto de Pesquisa Raman em Bangalore, na Índia.
A maior parte das galáxias massivas no universo devem abrigar no mínimo um buraco negro supermassivo em seus núcleos.
Quando duas galáxias colidem, seus buracos negros se juntam, formando uma dança colossal que resulta numa combinação de par. Esse processo é a mais intensa fonte de ondas gravitacionais no universo, que ainda precisam ser diretamente detectadas.
“As ondas gravitacionais representam a próxima fronteira da astrofísica, e sua detecção levará a novas ideias sobre o universo. É importante se ter a maior quantidade de informação possível sobre as fontes dessas ondas”, disse o Dr. David Roberts, um membro da equipe da Universidade de Brandeis.
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
This document summarizes an X-ray study of the supernova remnant G352.7-0.1 using data from XMM-Newton and Chandra observations. Prior observations revealed G352.7-0.1 has a shell-like radio morphology but center-filled thermal X-ray morphology, classifying it as a mixed-morphology supernova remnant. The new observations confirm the X-ray emission comes from the interior and is dominated by ejecta. Spectra from XMM-Newton are fit by a single thermal component with enhanced silicon and sulfur. Some Chandra spectra require a second thermal component to fit, with solar abundances providing a better physical model. No evidence of overionization was found. A neutron
Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Cons...Sérgio Sacani
Many recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the
anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a
constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space
Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitationalwave Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies
of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact
binaries, and a recently proposed scenario for massive black hole seed formation through multiple mergers of
stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost
unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through crosscorrelation with the cosmic microwave background (CMB) fluctuations. In particular, we find that a constellation
of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing
convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECI
Ähnlich wie Characterization of the Repeating FRB 20220912A with the Allen Telescope Array (20)
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Mending Clothing to Support Sustainable Fashion_CIMaR 2024.pdfSelcen Ozturkcan
Ozturkcan, S., Berndt, A., & Angelakis, A. (2024). Mending clothing to support sustainable fashion. Presented at the 31st Annual Conference by the Consortium for International Marketing Research (CIMaR), 10-13 Jun 2024, University of Gävle, Sweden.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
2. 2 S. Z. Sheikh et al.
any burst-to-burst periodicity (though two sources, FRB121102 and
FRB180916, show periodic activity windows, e.g., CHIME/FRB
Collaboration et al. 2020a; Pilia et al. 2020). Many FRB sources have
been precisely localized by interferometric arrays (Bannister et al.
2019; Marcote et al. 2020; Kirsten et al. 2022; Ravi & DSA-110 Col-
laboration 2023), which provide important clues to the nature of the
emitting objects and their host environments. Repeaters are particu-
larly valuable for interrogating the emission mechanism of FRBs, as
their bursts can be analyzed as a self-contained sample of observa-
tional data arising from a single physical object (e.g., Hessels et al.
2019; Li et al. 2021; Chamma et al. 2023; Jahns et al. 2023).
The emission mechanism of FRBs still remains a mystery (see
Cordes & Chatterjee 2019; Zhang 2020; Petroff et al. 2022; Bailes
2022, for recent reviews), though a consensus is emerging that
magnetars are likely responsible for at least a sub-population due
to an FRB-like event from a galactic magnetar (Bochenek et al.
2020; CHIME/FRB Collaboration et al. 2020b). For magnetar-related
classes of models, there is still considerable debate on the detailed
radiation mechanism, with various explanations distinguished by,
among other things, their distance from the progenitor magnetar
(Petroff et al. 2022). Magnetospheric models operate at a few neu-
tron star radii from the magnetar (e.g., Lu et al. 2020), while shock
models operate much further out, at characteristic scales of 1010 cm
(e.g., Metzger et al. 2019). Most radiation mechanism models for
repeaters sufficiently explain the broad features of repeating FRB
emission (e.g., coherent emission, an energy budget consistent with
repeating bursts, non-cataclysmic sources) and therefore will likely
be differentiated via more specific spectrotemporal behaviour.
The observed population of repeating FRBs does show consistent
spectrotemporal features, such as the tendency of emission from a
single burst to decrease in frequency over the duration of the burst,
often in discrete steps associated with distinct “subpulses” or “sub-
bursts” (Hessels et al. 2019). This so-called “sad trombone” effect, or
downward drift, is not an unbreakable rule, however, as others have
reported positive drift rates in some bursts (e.g., Kumar et al. 2022;
Zhou et al. 2022). For each FRB, features such as the duration, central
frequency, frequency extent, and drift rate can be combined with flux
and polarization information to reveal consistent properties across
bursts and sources. Specific spectrotemporal features such as upward-
drifting “happy trombones,” sub-burst periodicities (CHIME/FRB
Collaboration et al. 2023), or <100 ns sub-burst structure (Majid
et al. 2021; Nimmo et al. 2022) might provide the clues necessary to
understand the full nature of FRBs. For example, Zhou et al. (2022)
notes the similarity of drifting behaviour in FRBs to that of certain
pulsars, hinting at a potential similarity in emission mechanism or
environment. Similarly, the small emission regions (tens to thousands
of meters) implied by <100 ns sub-burst structure lends itself to a
magnetospheric origin (Nimmo et al. 2022).
On 2022 October 15, a new repeating source, FRB 20220912A,
was reported by McKinven & CHIME/FRB Collaboration (2022);
nine bursts at 400 MHz were detected by CHIME in a three day
period in September 2022. The original detection had inferred J2000
coordinates of RA = 347.29(4)◦, Dec = +48.70(3)◦. Other As-
tronomer’s Telegrams (ATels) soon followed, showing detections at
L-band (Herrmann 2022) and an improved localization from the
Deep Synoptic Array (DSA-110) at 23h09m04.9s +48d42m25.4s
(J2000) (Ravi 2022). This location is coincident with the potential
host galaxy PSO J347.2702+48.7066 (McKinven & CHIME/FRB
Collaboration 2022; Ravi 2022). The repeating FRB has since been
detected at frequencies from 300 MHz (Bhusare et al. 2022)1 (Fe-
dorova & Rodin 2022) to 2.3 GHz (Rajwade et al. 2022; Perera et al.
2022), with some large single-dish telescopes seeing L-band burst
rates of over 100 bursts per hour (e.g., Feng et al. 2022). Recent
published work on the source in Zhang et al. (2023) and Feng et al.
(2023) characterize this source as the fourth extremely active FRB,
but the first one in a relatively clean environment as derived from its
polarization information and steady DM, providing a unique labora-
tory for understanding which FRB properties come from the emission
mechanism intrinsically.
Repeating FRBs show varying behaviour across wide bandwidths,
for instance, periodicity in activity that is phase-delayed in time over
frequency for FRB 20180916B (e.g., Sand et al. 2022). They are also
limited in bandwidth (100s of MHz up to a few GHz; e.g., Gourdji
et al. 2019) around their unpredictable center frequencies. Given
these characteristics, wide bandwidth receivers and simultaneous
observation at different bands will be critical to characterize them.
The Allen Telescope Array (ATA) has both of these features, making
it a uniquely suited instrument for FRB observation.
In this paper, we report an observing campaign of FRB 20220912A
conducted with the ATA between October and December of 2022. In
Section 2, we summarize the current status of the refurbishment of
the ATA, describe the observational campaign of FRB 20220912A,
and detail the search pipeline used to detect and validate FRBs.
In Section 3, we discuss our methods for data pre-processing and
extraction of spectrotemporal properties. In Section 4, we use the
data and properties from the previous section to compute the all-sky
rate, quantify correlations between spectrotemporal properties, and
investigate potential sub-burst periodicity. Finally, we discuss our
results and conclude in Section 5.
2 OBSERVATIONS AND DATA
2.1 The Allen Telescope Array: Instrument Specifications
The ATA is a 42-element interferometer consisting of 6.1m dishes
hosted on the Hat Creek Radio Observatory in northern California
owned and operated by the SETI Institute, Mtn. View, CA. In late
2019, the instrument began a refurbishment program aimed at im-
proving the sensitivity and robustness of the telescope feeds and
revamping the Digital Signal Processing (DSP) system. A full de-
scription of the analog and DSP upgrades will be presented in Pollak
et al. (in prep.) and Farah et al. (in prep.) respectively, but here we
will include the essential details to accompany the observations of
FRB 20220912A.
Each ATA dish is an offset Gregorian and can slew in both the
azimuth and elevation direction. The refurbished “Antonio” log-
periodic feeds are dual-polarization and sensitive to a large instanta-
neous frequency range covering the 1 to 11 GHz band (Welch et al.
2009). Each feed is placed in a cryostat and is cooled to a temperature
of ∼ 70K. Analog signals from each antenna are amplified and sent
over optical fiber. Each antenna’s signal is then split and mixed to
produce up to 4 independently tunable signal chains, denoted ‘a’, ‘b’,
‘c’, and ‘d’.
Digitization of the antenna signals is performed on 16-channel
input Xilinx ZYNQ UltraScale+ Radio Frequency System-on-Chip
(RFSoC) boards, where data get channelized, packetized, and trans-
mitted to the network on a 100 GB ethernet link. A delay engine
and fringe rotator are also included as part of the firmware on the
1 There is also a claimed marginal detection at 111 MHz
MNRAS 000, 1–17 (2023)
3. ATA observations of FRB 20220912A 3
Table 1. Specifications of the Allen Telescope Array in Fall 2022
.
Parameter Value
Antenna diameter 6.1 meter
Longest baseline 300 meter
Frequency coverage 1-11 GHz
Primary beam FWHM (at 1GHz; at 11GHz) 3.5◦; 0.3◦
Synthesized beam FWHM (at 1GHz; at 11GHz) 4.2′; 0.38′
Processed bandwidth per tuning 672 MHz
Number of available simultaneous tunings 2
Number of simultaneous polarizations 2
Number of beamformed antennas 20
Field Programmable Gate Array (FPGA) boards such that voltage
data from all antennas are delayed and phase-centered relative to a
user-defined sky coordinate (usually the center of the ATA antenna
primary beam). Five RFSoC boards are currently deployed as part
of the prototype DSP system which supports the digitisation of 20
dual-polarization antennas over 2 frequency tunings. Upgrades to
outfit the entire ATA with newly refurbished feeds and deploy more
digitizers to cover all the available tunings are planned for the near
future.
Channelized voltages are received by a cluster of 8 compute
nodes where data are processed depending on the observer-selected
DSP backend. An xGPU-based, which accelerates cross-correlations
(x) using Graphical Processing Units (GPUs) (Clark et al. 2011),
can be selected to generate interferometric visibilities that can be
used for imaging and for delay and phase calibrating the beam-
former. Our beamformer, Breakthrough Listen Accelerated DSP En-
gine (BLADE), is a custom-built GPU-based beamformer that was
developed in-house, tested, and deployed on the ATA cluster (Cruz et
al., in prep.) and has since been used for novel science, such as track-
ing the reverse shock emission of gamma-ray burst 221009A (Bright
et al. 2023). Telescope users can customise the ATA backend ac-
cording to science cases. This includes selecting the time-integration
length of the correlator, setting the number of beams to produce with
the beamformer, and setting the polarization data output.
Table 1 contains a summary of the relevant instrument properties
for the FRB observations described here.
2.2 Observing Campaign
Just 56 minutes after the initial announcement of FRB 20220912A by
McKinven & CHIME/FRB Collaboration (2022), the ATA began a
follow-up campaign of the source. During the time period between 15
October 2022 and 31 December 2022, we observed the source in a se-
ries of 70 observations, with a median observation length of 8 hours,
divided into 30 minute scans. This led to a total observing time of 541
hours on-source. We ended the campaign when the source’s activity
had decreased, but not fully ceased, due to observing resource con-
straints. We recorded data with the 20-element beamformer, placing
a single phase-centered synthesized beam on the target at the center
of the primary beam; initially, we used the inferred J2000 coordinates
from the CHIME detection of FRB 20220912A, then switched coor-
dinates to the updated DSA-110 coordinates once they were available
on 25 October 2022. Given the synthesized beamsize of the ATA
at 2 GHz (approximately 2 arcmin), the original FRB coordinates
would have placed the true source at the edge of the beamformed
beam, which affected the first 31 hours of observation. Sheikh et al.
(2022) described the detection of 8 bursts from FRB 20220912A
with the ATA; the 8 bursts in that announcement are included in this
work.
We exercised the ATA’s tuning flexibility to observe the source at
two different 672 MHz tunings simultaneously. The center frequen-
cies of the tunings varied at the beginning of the campaign, but set-
tled at their final values of 1236 MHz and 1908 MHz on 4 November
2022. This setting allows for the two tunings to provide continuous
frequency coverage from 900–2244 MHz. Before 4 November 2022,
12 sessions had tunings of 1400 MHz and 3000 MHz, 2 sessions had
tunings of 1400 MHz and 6000 MHz, and 1 session had tunings of
1150 MHz and 1850 MHz — this amounts to 76 / 541 hours of data
recorded at the non-final central frequencies.
Before every observing session, we observed a phase calibrator
(3C48, 3C286, or 3C147) in the correlator mode to assess sensitivity
and calibrate the instrument with updated delay and phase solutions
prior to science observations. In addition, from 7 November 2022
until the end of the campaign, we added an observation of pul-
sar J0332+5434 for general system validation and validation of the
SPANDAK pulse detection pipeline described in Section 2.3.
2.3 Searching for FRBs
The ATA beamformer used for the observations described in the
previous section currently produces Stokes I 32-bit SIGPROC “fil-
terbank”2 files at a frequency and time resolution of 0.5 MHz and
64µs, respectively. These data were not coherently dedispersed to
any particular DM during data-recording, but were stored for off-
line FRB searching. The beamformer is capable of producing cross-
polarisation data products that can enable polarization studies. How-
ever, given the intricate nature of polarisation calibration, we de-
liberately chose not to record individual polarisations for this work
(though we intend to do so in future studies). Moreover, efforts are
currently underway to implement a beamformer mode which sup-
ports coherent dedispersion.
In this project, we used the SPANDAK pipeline (Gajjar et al. 2022),
which is a wrapper for HEIMDALL, a GPU-accelerated search code
for dispersed signals in radio astronomical data (Barsdell 2012).
SPANDAK implements additional filtering and candidate evaluation
procedures on the HEIMDALL outputs and produces tables of burst
candidates along with diagnostic plots that are later visually reviewed
by an observer.
We first decimate the filterbank files in bit depth from 32-bit to
8-bit so they are compatible with the existing format requirements
for HEIMDALL. We then splice the seven nodes of data for each of
the two tunings together, creating one 8-bit filterbank file covering
the entirety of the tuning centered at Local Oscillator (LO) b and
another covering the entirety of the tuning centered at LOc. Due to
the data volume and processing time, we opted not to perform Radio
Frequency Interference (RFI) removal before searching.
We assign a DM search range of ±10% from the nominal disper-
sion measure of 219.46 pc cm−3 as reported by the CHIME repeater
catalog3, with a DM step size calculated such that the Signal-to-
Noise Ratio (SNR) loss between DM trials is no more than 0.1%. We
then run SPANDAK with a SNR threshold of 10, a boxcar maximum
width of 216 samples (4.194 seconds), and a maximum-candidates-
per-second (maxCsec) value of 15, which is slightly higher than the
SPANDAK default. The maxCsec parameter is observatory and band
dependent as it is strongly correlated with the RFI environment. For
2 https://sigproc.sourceforge.net/sigproc.pdf
3 https://www.chime-frb.ca/repeaters
MNRAS 000, 1–17 (2023)
4. 4 S. Z. Sheikh et al.
these frequencies at the ATA, we determined that 15 was an ap-
propriate value via test observations of J0332+5434. We execute the
search code over each spliced tuning independently, corresponding to
a fixed search bandwidth of 672 MHz. The incoherent dedispersion
and searching code is then executed and logged. More information
about how the SPANDAK candidate plots are constructed can be found
in Figure 9 of Gajjar et al. (2021).
The median number of top candidates per observing session was 9,
where a top candidate is a HEIMDALL candidate given at least a B–C
rank by SPANDAK due to its broadband characteristics and trial DM-
vs-SNR response. The low number of candidates made additional
filtering for false-positive RFI unnecessary in most cases.
In 541 hours of observation, we detect 35 bursts from
FRB 20220912A. All 35 bursts were detected in LOb, the lower
672 MHz tuning, with none detected (or visible simultaneously in
dedispersed archives) in LOc. This is consistent with low detection
rates at S-band and non-detections in C-band (e.g., Kirsten et al.
2022). Dynamic spectra for all the bursts detected with the ATA are
shown in Figure 1. As suggested by the single-tuning detections, the
bursts from FRB 20220912A are highly spectrally limited, which
was similarly observed in FRB 20180916B (Sand et al. 2022) and
FRB 20121102A (Law et al. 2017) — a deeper investigation of spec-
tral extent is performed in Section §4.
The timeline of our detections is visualized in Figure 2.
3 DATA REDUCTION
3.1 File Preparation
Once we have identified an FRB within one of the 30-minute
long filterbank files as described in Section §2.3, we crop the
filterbank in time, centering on SPANDAK’s reported trigger time
for the burst. We choose a 10-second cropping length, to capture the
entire burst with dispersive delay and provide context for noise and
RFI properties.
Next we convert the cropped filterbanks to archive files
with DSPSR (van Straten & Bailes 2011), using the best-fit SNR-
maximizing DM of the burst from SPANDAK contained in the meta-
data. This choice visually corresponded with structure-maximizing in
the dedispersed waterfall plots for all but two of the bursts. For these
two bursts (#24 and #25), we found that the SPANDAK over-disperses
the burst, as evidenced by the morphology of the subcomponents and
the anomalously large reported DMs (224.94 and 223.24 pc cm−3,
respectively). We thus set their archive file DM to the average from
the other 33 bursts, at 219.775 pc cm−3. All archive files have the
time axis of the file (10 seconds) read in as “phase” but are otherwise
equivalent to archive files used for other radio pulsar applications.
3.2 Calculating Flux and Fluence
Using the calibration measurements described in Section 2.2, we
calculate the flux and fluence of each of the 35 FRBs in the sam-
ple. First, we obtain the System Equivalent Flux Density (SEFD) of
each observation. All three flux calibrators in this dataset have flux
models from Perley & Butler (2017), from which we obtain expected
spectral flux densities 𝑆exp at the central frequencies of both LOs.
We calculate the SEFD for each antenna-polarization combination
(antenna 𝑥, polarization 𝑦) as follows:
SEFD𝑥,𝑦 = (𝐺2
cal × 𝑆exp)−1
(1)
Where 𝐺cal is the gain from the associated calibrator file, in units of
Jy−1, computed using the Common Astronomy Software Application
(CASA) gaincal task (Bean et al. 2022). We then average each of
the antenna-polarization SEFDs to get the beamformer SEFD:
SEFDbeamformer =
Σ𝑥,𝑦SEFD𝑥,𝑦
𝑁𝑥,𝑦
𝑁el
(2)
Where 𝑁𝑥,𝑦 = 40 (the number of antenna-polarization combina-
tions) and 𝑁el = 20 (the number of elements in the beamformer). This
results in a polarization-averaged SEFDbeamformer of 387 ± 38 Jy.
This number is in agreement with earlier tests conducted with the
instrument, and details about recovering flux scales and beamformer
efficiency for the ATA will be presented in a forthcoming paper
(Farah et al., in prep.). For observations listed here, we used a uni-
form weighting of all antennas for the beamformer.
From this SEFD, we can use the radiometer equation to get the
minimum detectable flux density 𝑆𝜈,min of this work:
𝑆𝜈,min =
(SNR)(SEFD)
√︁
𝑛pol𝜏Δ𝜈
(3)
Where 𝜏 is the duration of an FRB, Δ𝜈 is its frequency extent,
and 𝑛pol is the number of recorded polarizations (in this case, 2).
Therefore, 𝑆𝜈,min for a SNR threshold of 10, an SEFD of 387 Jy,
and a fiducial FRB duration and bandwidth of 1 ms and 672 MHz,
is 4.7 Jy.
We detected 35 bursts in 541 hours of observing, implying an
average burst rate above 4.7 Jy of 6.47
+1.29
−1.09
× 10−2 h−1, where the
uncertainties represent 1-sigma Poisson errors (Gehrels 1986).
We use the Python binding for PSRCHIVE (Hotan et al. 2004)
to load the data as dynamic spectra, incoherently dedisperse each
array to the SPANDAK DM described in Section 3.1, and remove the
baseline. We then average each array in frequency to get a timeseries
burst profile, and normalize it by subtracting the median and dividing
by the standard deviation of a noise region consisting of ±1000 time
bins (64 ms) on either side of the burst.
At this point, we define the boundaries in the timeseries from
which to extract SNRs, fluxes, and fluences. Only 7 FRBs consist of
a single component; the rest of the sample shows complex sub-burst
structure. A sub-burst is qualitatively defined here as a significant
local maximum in intensity in an FRB’s profile, especially if that
structure seems distinct in frequency from the neighboring emis-
sion in the dynamic spectrum. We opt here to measure each of the
sub-bursts individually, as not to downweight the flux by averag-
ing over the periods between sub-bursts. The sub-burst delineations
determined here are the same ones that are used in the process of
extracting spectral properties of sub-bursts, described in Section 3.3.
Using the sub-burst bounds and the normalized profile defined
above, we obtain the SNR with SNR =
Σ𝑝
√
𝑁
, where 𝑝 is the normal-
ized profile and 𝑁 is the number of points across the profile (i.e., the
duration of the sub-burst). To transform the SNR into the flux in Jy,
we can incorporate the SEFD as follows:
𝑆Jy =
SEFD × SNR
√︁
𝐵 × 𝑁𝑃 × 𝑁 × 𝑡samp
(4)
where 𝐵 is bandwidth of the sub-burst, 𝑁P is the number of polar-
izations, and 𝑡samp is the sampling time. Finally, we convert 𝑁, the
duration in bins, into a duration in ms and multiply by 𝑆Jy to get the
fluences in Jy-ms.
MNRAS 000, 1–17 (2023)
5. ATA observations of FRB 20220912A 5
Figure 1. Dynamic spectra (or “waterfall” plots) for all the bursts from FRB 20220912A detected using the Allen Telescope Array, the frequency-averaged pulse
profiles, and the time-averaged spectra. The red-shaded regions in the time series plots denote the time span of the defined sub-bursts, with red vertical lines
demarcating adjacent sub-bursts.
MNRAS 000, 1–17 (2023)
6. 6 S. Z. Sheikh et al.
Figure 1. Continued.
Figure 2. Cumulative observing time on FRB 20220912A over the months of the campaign (black line), with detections marked in dashed blue lines. The red
shaded region indicates observations for which the higher tuning was unavailable, restricting our bandwidth by a factor of two. The average interval between
observations was 1.11 days, with a maximum interval of 3.80 days and a minimum interval of a few hours.
The SNRs, fluxes, and fluences derived here are included in Table
2 (at the end of the paper). Uncertainties in the DM were derived by
applying a sliding boxcar with the parameters used by SPANDAK in
the original detection and providing the width of the best-fit Gaussian
to the DM-SNR curve. Uncertainties in the fluxes and fluences are
calculated by propagating the uncertainty on the mean SEFD.
It should be noted that the first 3 FRBs in the sample were detected
while the synthesized beam was centered on the original, offset co-
ordinates. To address that, we modeled the shape of the synthesized
beam at the topocentric coordinates for the aforementioned bursts.
We then corrected the measured flux densities with the calculated
attenuation values of 0.5 dB, 0.5 dB, and 1 dB for bursts 1, 2, and 3
respectively.
Some of the flux values in the downsampled 8-bit filterbank
files were clipped to the highest intensity bin, implying that we were
underestimating the total flux by some amount for the brightest FRBs.
To estimate the impact of the clipping, we looked at the percentage of
pixels in the highest intensity bin for the highest SNR FRB (#25). For
this particular FRB, approximately 3% of the pixels were clipped as
seen when plotting the pixel intensity distribution histogram. Recov-
ering the original values (i.e. before resizing to 8-bit depth) is almost
impossible given that the original 32-bit, higher dynamic range data
products were deleted. However, we still attempted to quantify the
MNRAS 000, 1–17 (2023)
7. ATA observations of FRB 20220912A 7
effects of pixel clipping by assuming that the intensity distribution,
at the top end, follows a continuous dampened trend. We fit the inten-
sity histogram, and “redistribute” the clipped pixels by extrapolating
beyond the 8-bit clipping point, and then integrate the intensities and
measure the flux. By doing so, we found that we were only underes-
timating the flux by approximately 3% for this FRB. Given that this
is the most extreme example in our sample, we do not correct for this
effect in the dataset.
3.3 Extracting Spectral Properties with frbgui
Some parameters of interest for the 35 FRB sample are calculated
from the original archive files, but some spectrotemporal properties
such as bandwidth and duration must be extracted with additional
processing, especially for bursts with multiple sub-components. We
used the spectrotemporal FRB code frbgui (Chamma et al. 2023)
to extract these parameters.
We load the archive files into Python, dedisperse, and remove
baseline as described in the previous Section 3.2. For each FRB,
we defined start time and end time indexes in the original archive
file — we crop the array to ± 100 bins (6.4 ms) on this range. Fi-
nally, the files are written out as dynamic spectra with accompanying
metadata containing information about the time axis, frequency axis,
dispersion measure, and various units.
We open these dedispersed and cropped files with frbgui. For
each file, we define a DM grid covering the original SPANDAK DM ±
0.5 pc cm−3, sampled at 0.01 pc cm−3 intervals. If the average DM
of the whole sample would fall outside of this grid, we extend it by
another ± 0.5 pc cm−3 in the relevant direction. We then optionally
perform a series of tasks to improve the SNR of the burst:
• Subtract a background sample from the entire dynamic spec-
trum: This background sample is usually selected to be the first few
milliseconds of the file before the burst begins. This helps remove
narrowband RFI.
• Add a frequency mask range: For bursts that do not cover the
entire bandwidth (most of them, as per Figure 1), we can mask up to
hundreds of MHz of bandpass where there is no FRB signal in order
to improve the SNR.
• Remove remaining RFI: For bursts with significant RFI, we
implemented built-in RFI-masking with a spectral kurtosis - Sav-
itzky–Golay (SK-SG) filter (with a polynomial order of 𝜎 = 3 and
a a window-size of 15 samples), which improved the SNR. For less
affected bursts, however, this removed the brightest parts of the true
FRB signal and was not used.
• Downsample in time and frequency: By downsampling, or fre-
quency averaging and time integrating the dynamic spectrum, we can
improve the SNR — this is especially necessary for faint FRBs and
was already part of SPANDAK’s routine for finding these fainter FRBs.
We select time and frequency downsampling factors that are evenly
divisible into the length of the array axes, while still endeavoring to
keep enough resolution to be confident of e.g., drift rates.
We then manually demarcate burst splitting with frbgui’s inter-
active interface. Given that FRBs have been shown to have sub-bursts
and structure on the order of microseconds (Nimmo et al. 2022), and
that we are downsampling to increase SNR, there are likely fine-
structure details that we cannot resolve in our dataset. Nevertheless,
we do delineate the sub-bursts that are visible given our resolution,
and find FRBs with up to 7 distinct components in our 35 burst
dataset.
Finally, weuse anon-linear leastsquares algorithm4 to performa 6-
parameter 2D Gaussian fit to the 2D auto-correlation of the dynamic
spectrum for the entire array, and then for the limited sub-arrays
delineated in time by each sub-burst start and stop defined previously.
Fitting to the auto-correlation increases the SNR and mitigates the
effect of e.g., scintillation and RFI in the parameter measurements
(see Chamma et al. 2023, for more details about this operation). For
each DM in the grid, the fitter returns the bandwidth, duration, and
sub-burst slope for each of the sub-bursts, as well as the bandwidth,
duration, and drift rate (in MHz ms−1) of the overall burst, with
their associated errors. In some cases, the fitter does not converge on
the correct parameters for the burst. We visually reviewed each fit
(for every DM-sub-burst combination) in the frbgui interface and,
where necessary, implemented a refit by manually inputting an initial
guess based on the correct preceding fits.
The center frequency, duration, and bandwidth information for
each sub-burst are shown in Table 2. Reported uncertainties in the
duration are equal to the time bin size after scrunching in the dynamic
spectrum used for the spectral property fitting.
4 DATA ANALYSIS
4.1 Spectrotemporal Analysis
Using the FRB and sub-burst characteristics extracted in Section
3, we can investigate population-scale features of our dataset. The
center frequencies, durations, and bandwidths for all 101 sub-bursts
in the set are displayed in Figure 3.
For all linear fits in Sections 4.1.2–4.1.5, we use the following
methodology. In most cases, we have an independent variable 𝑥, a
dependent variable 𝑦, and heteroscedastic errors in each variable 𝑥err
and 𝑦err. We account for this heteroscedasticity with a bootstrap-
ping technique. We employ an ordinary least squares (OLS) fitting
method that incorporates robust covariance estimators (specifially,
the HC1 estimator from MacKinnon & White 1985). In each of
10000 bootstrapped trials, we draw each value of 𝑥 or 𝑦 from a nor-
mal distribution with a width of 𝑥err or 𝑦err respectively, and then
use the OLS fitting method to get a value for the slope and its asso-
ciated 𝑅2 value (the square of the Pearson correlation coefficient, to
quantify how much variance in the dependent variable is explained
by the independent variable).
For each fit, we report a) the mean of the 10000 slopes from the
trials above b) the mean of the 10000 standard errors of the slope,
and c) the mean of the 𝑅2 values of the 10000 trials. We calculate
the significance of these correlations by running an additional 10000
trials where we permute the data, i.e., randomly shuffle the 𝑦 values
and then re-assign them to the 𝑥 values. The p-value is then the
percentage of permuted outcomes that meet or exceed the absolute
value of the mean 𝑅2 described above. Here, we use 𝑝 < 0.05 as our
threshold for statistical significance.
4.1.1 Burst Energy
To compare our sample with the energy distribution of 128 bursts
seen by the Green Bank Telescope (GBT) (Feng et al. 2023), we can
convert the fluences from Section 3.2 into isotropic equivalent sub-
burst energies, using the redshift and luminosity distance from Planck
Collaboration et al. (2016); Ravi et al. (2022), which assumes Planck
2016 cosmology. We find a median sub-burst energy for our sample
4 Via scipy.optimize.curve_fit
MNRAS 000, 1–17 (2023)
8. 8 S. Z. Sheikh et al.
Figure 3. The distributions of center frequency in MHz, duration in ms, and
bandwidths in MHz for each of the 101 sub-bursts in the dataset. We see
the majority of FRBs reside at the lower end of the bandpass, have < 2 ms
durations and show bandwidths of a few 100 MHz.
of 1 × 1039 erg, approximately two orders-of-magnitude greater than
the median from Feng et al. (2023), although approximately on-par
with their brightest bursts. This is consistent with the lower sensitivity
of the ATA. The brightest sub-burst in our sample, from #25, has an
energy of 1.8× 1040 erg; the brightest burst, combining all subbursts
(also #25), has an isotropic energy of 5 × 1040 erg.
4.1.2 Center Frequency vs. Bandwidth
To test the correlation between the center frequency of a sub-burst
and its bandwidth, we first remove any FRB from the set whose sub-
bursts significantly intersect the edge of the band by visual inspection
of the de-dispersed dynamic spectra. This results in a set of 55 sub-
bursts for which we evaluate a linear fit. We find a positive, linear
correlation between center frequency and bandwidth with a slope of
0.28 ± 0.04, as shown in Figure 4. The 𝑅2 for the fit between the
center frequency and bandwidth is 0.533 and the p-value is < 10−4.
This slope is consistent within a factor of two of the slope of
0.14 ± 0.004 found by Chamma et al. (2023) for FRB 20121102A,
although different sources would not necessarily be expected to have
the same slope. The center frequency and bandwidth relationship
described here also appears consistent with the 1000-burst dataset
from Zhang et al. (2023).
Figure 4. Center frequency in MHz versus bandwidth in MHz for 55 sub-
bursts from FRB 20220912A (black) and their best-fit line (blue). 1-𝜎 fit
errors derived by frbgui are shown in both center frequency and bandwidth
for the points used in the linear fit, which were accounted for during the
bootstrapping. We confirm the expected positive linear relationship between
these two properties.
4.1.3 Center Frequency and Bandwidth vs. Time
A unique feature of our dataset was the relatively steady rate of data
acquisition over the two months of the campaign; this can be seen in
the smooth slope of the cumulative observing time in Figure 2. This
allows us to interrogate changes in the properties of the 101 sub-
bursts from FRB 20220912A over time. We see a decrease in both
the center frequency and bandwidth over the course of the campaign
(Figure 5). The center frequency decreases at a rate of 6.21 ± 0.76
MHz per day, with a corresponding 𝑅2 of 0.311 and a p-value of
< 104. This trend is echoed by the bandwidth, which decreases
2.08 ± 0.38 MHz per day, with a corresponding 𝑅2 of 0.191 and a
p-value of < 104, due to their inherent relationship shown in Figure
4. There were no similarly obvious changes in flux, duration, or DM
over the campaign.
Other repeaters have been observed to have varying activity levels
at different frequency ranges. For example, FRB 20180916B shows
activity in the 1000 MHz range 3 days before activity peaks in the
100 MHz range (Pleunis et al. 2021a). Pearlman et al. (2020) also
find that apparent FRB activity is strongly affected by which frequen-
cies are being recorded, with FRB 20180916B again showing this
behaviour particularly strongly. However, this marks the first trend
in frequency over time for a so-far non-periodic (as per Zhang et al.
2023) repeating FRB.
The residuals from the linear fit of central frequency over time
in Figure 5 do merit discussion. We find some remaining structure
in the residuals, where the best-fit model underestimates the center
frequency at the beginning of the campaign and overestimates the
center frequency at MJD 59890. Without an underlying model to
compare to, we do not attempt to fit a more complex function to
the data, but do note this behaviour as something to be investigated
in future studies. In addition, the residuals in this linear fit are not
homoskedastic: the scatter around the best-fit line decreases over the
campaign. These heteroskedastic errors should raise some questions
about the extension of this trend past the bottom of our bandpass.
Specifically, it seems possible that there is a several hundred MHz
wide, downward drifting “activity window” in frequency, that drifts
out of our bandpass over the campaign. This leads to the apparent
shrinking of the scatter at the end of the linear fit, and implies that the
MNRAS 000, 1–17 (2023)
9. ATA observations of FRB 20220912A 9
Figure 5. Two FRB 20220912A dataset parameters — center frequency and bandwidth — plotted over time, in MJD, from the beginning of the campaign to
the end of the campaign (a time period of approximately 60 days). Panel a) indicates that the central frequency of the FRB decreases through the campaign
(with residuals from the fit and a LOWESS non-parametric guideline shown below in blue). Panel b) shows the same decrease over time for bandwidth, which
is understandable given the relationship between bandwidth and center frequency shown in Figure 4.
actual slope in the central frequency may be steeper than 6.2 MHz
per day.
4.1.4 Center Frequency vs. Drift Rate
Other repeaters have shown a correlation between center frequency
and drift rate, the linear decrease in sub-burst center frequency over
time. We use the values derived by frbgui in Section 3.3 to assess
whether we see this same correlation in the FRB 20220912A data. It
should be noted that no FRBs in our sample show upward-drifting
bursts (e.g., Kumar et al. 2022).
To construct a subsample with reliable drift rate measurements,
we must first remove all of the single-component FRBs, which do
not have a defined drift rate. In addition, the Auto-Correlation Func-
tion (ACF) method for sub-burst center frequency determination will
underestimate the center frequencies of components that intersect
the top edge of the bandpass, and correspondingly overestimate the
center frequencies of components that intersect the bottom edge of
the bandpass. Both effects lead to an underestimation of the drift rate:
therefore, we remove any FRBs that intersect the edges of the band-
pass, bringing the subsample to 11 FRBs. Finally, we wish to remove
any FRB where the ACF measured the sub-burst slope of the bright-
est component instead of the drift rate across multiple components,
which can occur in FRBs with large SNR variation across sub-bursts.
This effect is visible in the 2D-ACFs, and can be confirmed as an
anomalously high drift rate that is consistent with a single sub-burst’s
slope. For this reason, we additionally remove FRBs #3, #6, and #18.
We plot the drift rates for the 8 remaining FRBs (#1, #4, #8, #10,
#20, #23, #24, and #25) against their center frequencies in Figure
6 and do not find a statistically-significant correlation. We used a
𝑁 = 105 trial bootstrap for this correlation, due to p-values that were
near the threshold. The bootstrapping OLS routine finds a slope of -
0.189±0.07 MHz ms−1MHz−1 and an 𝑅2 of 0.502, but the p-value of
0.052 is not significant. This is consistent with the data, considering
the small-number statistics resulting from only 8 FRBs in the fit.
Other repeating FRBs demonstrate a trend of steeper drift rates
with frequency. For FRB 20180916B, compilations of studies across
wide bandwidths have shown a drift rate change of −0.02–−0.03
MHz ms−1MHz−1 with frequency (Pastor-Marazuela et al. 2021;
Sand et al. 2022). Meanwhile, for FRB 20180301A (at frequencies
an order-of-magnitude higher), Kumar et al. (2023) find a drift rate
change of −0.14 MHz ms−1MHz−1 with frequency, over approx-
imately the same frequency range as this work. Using MeerKAT,
Platts et al. (2021) find a similar drift rate change with frequency,
-0.147 ± 0.014 MHz ms −1MHz−1, for FRB 121102. It should be
noted that a quadratic fit is favoured when data covers a larger range
of frequencies (Wang et al. 2022; Chamma et al. 2023). Given that
our measurement was not significant, we cannot add to this popu-
lation of results with FRB 20220912A in this work; regardless, the
consistency of the sign and general relationship of frequency and
drift rate over this population of repeaters hints at a persistent feature
in at least a subclass of FRBs that must be explained by any proposed
emission mechanism.
Sub-burst slope and drift rate can follow similar relationships (e.g.,
Rajabi et al. 2020; Chamma et al. 2023). However, we see no cor-
relation between subburst slope and duration, or subburst slope and
center frequency, in this dataset. Given the scatter in the measure-
ments and the lack of bursts at other bands to constrain model fits,
this is not unexpected.
4.1.5 Center Frequency vs. Temporal Duration
It has been noted that higher frequency sub-bursts seem to have
shorter temporal durations, which is only observable across GHz of
bandwidth (e.g., Platts et al. 2021). Gajjar et al. (2018) notes that
the widths are considerably narrower (about an order of magnitude)
at 8 GHz compared to 1 GHz for FRB 121102, but that the effect
does not seem consistent with broadening due to scattering from
turbulent plasma along the line-of-sight. Here, we do observe a slight
downward trend in duration with increasing frequency, as shown in
Figure 7. The associated linear fit has a slope of (−9.3 ± 3.3) ×
10−4 MHz ms−1, an R2 value of 0.067 (indicating wide scatter over
the ∼700 MHz available in these observations), and a p-value of
0.0098. Given the low correlation, this result should be taken only
as an indication of consistency with the previously-observed trend
of shorter durations at higher central frequencies. Given the channel
MNRAS 000, 1–17 (2023)
10. 10 S. Z. Sheikh et al.
Figure 6. Drift rates in MHz ms−1 plotted against frequency in MHz for
8 FRBs from FRB 20220912A that a) had more than 1 subcomponent b)
did not intersect either edge of the bandpass and c) had subcomponents of
similar-enough SNRs to allow for a correct drift rate fit from the 2D ACF
of the dynamic spectrum. Visually, there is a downward trend (increasing
magnitude of drift) with increasing frequency and we show the best-fit line
from a linear fit (black), but we do not find that this trend is significant
.
Figure 7. Duration in ms plotted against frequency in MHz for our full sample
of 101 sub-bursts from FRB 20220912A. Note the slight decrease in duration
over the bandpass.
width and the FRB DM, the expected smearing due to dispersion at
the bottom of the ATA band is ∼ 0.9 ms.
4.1.6 Scattering
We do not observe any significant scattering behaviour in the wa-
terfall plots in Figure 1, though we cannot constrain scattering
timescales less than several hundred µs at these frequencies, due
to our sampling time of 64 µs. This is consistent with the nominal
scattering value of ≤ 15 ms at 400 MHz for this source as reported
by Bhusare et al. (2022), which would imply, given a Kolmogorov
scaling with 𝛼 = 4.4, an expected scattering timescale of ≤60 µs.
4.2 Repeating Rate Function and All-Sky Rate
We show the cumulative repeating rate function 𝑅(> 𝐹) for
FRB 20220912A in Figure 8, where 𝐹 is the fluence of each FRB
(which may contain multiple sub-bursts). We fit the observed flu-
ence distribution with a power-law function using the powerlaw
package provided by Alstott et al. (2014) based on Clauset et al.
(2009). The package uses the maximum likelihood method to opti-
mize the power-law slope 𝛾 ≡ −d ln[𝑅(> 𝐹)]/d ln𝐹 and further uses
the Kologorov-Smirnov test to optimize the minimum fluence 𝐹min
above which a power-law provides the best description (see Clauset
et al. 2009, for the method descriptions).
When restricting the minimum fluence to be in the range from 40
to 150 Jy ms (roughly corresponding to a minimum SNR between
∼40 and ∼150 for burst duration of ∼1 ms), we find the optimized
minimum fluence to be 𝐹min ≃ 130 Jy ms. We also find the best
power-law above this minimum fluence to be
𝑅(> 𝐹) = 3.3 × 10−2
h−1
(𝐹/𝐹min)𝛾
, 𝛾 = 1.08, (5)
and the standard deviation of the power-law slope is 𝜎 = 0.25.
The slope is not well constrained by the current small sample but
it is consistent with the power-law slope of the FRB luminosity (or
energy) function (e.g., Luo et al. 2018; Lu & Piro 2019; James
et al. 2022; Shin et al. 2023). We also tried fitting the ATA sample
by an exponentially truncated power-law described by 𝑅(> 𝐹) ∝
𝐹𝛾 exp(−𝐹/𝐹max), and the best fit result is 𝛾 ≃ 0.0 and 𝐹max ≃
570 Jy ms. Although the likelihood ratio test shows that a truncated
power-law fit is preferred with a 𝑝-value of 0.06 — meaning that
there is a 6% chance that the improvement in the likelihood is due to
random fluctuations, the truncated power-law model has an additional
free parameter and hence a truncation is not required by the current
data.
We then compared the repeating rate function for FRB 20220912A
with the cumulative all-sky rate function at high fluences, which is
provided by the ASKAP Fly’s Eye survey (Shannon et al. 2018).
Using the same method as outlined above, we find that the all-sky
rate function can be described by the following best-fit power-law
function above an optimized minimum fluence of 𝐹min = 50.6 Jy ms,
𝑅as(> 𝐹) = 1.6 h−1
(𝐹/𝐹min)𝛾as , 𝛾as = 1.54, (6)
and the standard deviation of the power-law slope is 𝜎as = 0.34. De-
spite that 𝛾as is statistically weakly constrained, we do theoretically
expect the fluence distribution to be close to the Euclidean value of
𝛾 = 1.5 because the ASKAP bursts are from the local Universe and
the entire FRB population has a maximum specific energy (see e.g.,
Macquart & Ekers 2018; Lu & Piro 2019; Shin et al. 2023).
It should be noted that the specific energy of the brightest burst
(𝐹 = 1128 Jy ms) detected in our sample is
𝐸 ≃
𝐹 × 4𝜋𝐷2
L(𝑧)
(1 + 𝑧)2
≃ 1.5 × 1032
erg Hz−1
, (7)
where we have used the Planck Collaboration et al. (2016) cosmolog-
ical parameters for the luminosity distance 𝐷L and a source redshift
of 𝑧 = 0.077 provided by Ravi et al. (2022). This burst is among
the most intrinsically bright ones observed to-date (e.g., Ryder et al.
2022; Shin et al. 2023). As can be seen in Figure 8, the repeat-
ing rate function of FRB 20220912A must have a cut-off at fluence
𝐹max ≲ 104 Jy ms for this source to be consistent with the all-sky
fluence distribution extrapolated from the ASKAP measurement as-
suming 𝛾as = 1.5 (and additionally assuming that the repetition rate
of this source is constant). Such a cut-off is also consistent with the
inferred maximum specific energy 𝐸max ∼ 1032 to 1033 erg Hz−1 in
the FRB luminosity/energy function (Shin et al. 2023). Further long-
term monitoring of FRB 20220912A is needed to test if the repeating
rate function indeed has a cut-off.
MNRAS 000, 1–17 (2023)
11. ATA observations of FRB 20220912A 11
Figure 8. Fluence distributions of the ATA sample of bursts from
FRB 20220912A (thick black line) and the ASKAP Fly’s Eye sample (thin
black line). The vertical axis shows the cumulative rate, as computed by the
raw number of detections divided by the total on-source time. The total ex-
posure of the ASKAP Fly’s Eye survey is 5.1 × 105 deg2 h (Shannon et al.
2018), which is converted into an all-sky equivalent exposure time of 12.4 hr
— the thin black line shows the all-sky rate as inferred from the ASKAP sam-
ple. The flattening of the distributions at the low fluence end (≲ 100 Jy ms
for the ATA sample and ≲ 50 Jy ms for the ASKAP sample) is likely due to
incompleteness of the surveys. The steepening at the high fluence end is due
to insufficient exposure times. The blue dashed and orange dash-dotted lines
show the best-fit power-law and truncated power-law models to the ATA data,
respectively. The red dotted line shows the best-fit power-law model for the
ASKAP data.
On the other hand, we also see from Figure 8 that FRB 20220912A
contributes at least a few percent of the all-sky rate above fluence
of ∼ 100 Jy ms. Although prolific repeaters like FRB 20220912A
and FRB 20121102A represent a minority of all FRB sources, they
contribute a significant fraction of the all-sky rate. On the other hand,
many of the > 100 Jy ms sources detected by the ASKAP Fly’s Eye
did not show repetitions even with sensitive follow-up observations.
This means that the brightest FRBs in the sky are contributed by
the most active repeaters as well as by the less active ones. This
further restricts the maximum fluence of FRB 20220912A to be likely
significantly less than 104 Jy ms.
4.3 Characteristic Timescales and Sub-burst Periodicity
Given that so many of our FRBs are multi-component (29/35), we
investigate whether or not the sub-bursts show any consistent inter-
pulse spacings. In particular, FRB #10 shows 4 sub-bursts that are
bright and appear evenly-spaced, hinting at sub-burst periodicity.
For both a general characteristic timescale analysis and a periodicity
analysis, we begin with the numpy arrays produced in Section 3.3,
and average over the frequency axis to get a timeseries profile. We
then median-subtract and apply a 5th-degree polynomial Savitzky-
Golay filter with a window-size of 21 samples (Savitzky & Golay
1964). The smoothing filter is applied to make peak-finding possible
in Section 4.3.1, but does attenuate potential short-period behaviour
(≲ 0.13 ms) in the FRB profile.
4.3.1 Characteristic Timescales
To characterize significant timescales in each FRB, we calculate the
ACF of the smoothed FRB profile with scipy. This allows us to
be more sensitive to non-sinusoidal signals with fewer repetitions in
short timeseries than a power spectrum (e.g., a Leahy-normalized
power spectrum, see CHIME/FRB Collaboration et al. 2022) while
still performing a similar function.
We then find the tallest local maximum in the ACF with a required
minimum peak width of 𝑤ACF > 2 bins (to avoid single-bin noise
fluctuations).This corresponds to the lag time 𝑝ACF which contains
the most power in the ACF — if the FRB is generating the peak in
the ACF, this is likely representative of the delay in sub-bursts for a
two-component FRB. At this stage, 2 of the 35 FRBs were removed
from the sample due to not having any peaks in their ACFs.
RFI is often periodic and could create a false-positive periodicity in
the ACFs from the previous step. Therefore, we perform a bootstrap
resampling noise-permutation test as a crude filter for ACF peaks
that are not coming from the FRB signal itself. Each file contains
100 channels of noise before and after the FRB, which constitutes
25% or more of each file (depending on the variable FRB duration;
mean=42%). For each FRB, we perform 1000 trials where the noise
arrays before and after the FRB signal are randomly shuffled, and
then perform the median-removal, smoothing, ACF, and peak-finding
steps as for the original FRB profile. If the mean of the set of 1000
noise-scrambled ACF peaks still falls within 10% of the original,
with a standard deviation that is less than the width of the peak 𝑤ACF
from the original ACF, we treat this as a spacing that is inherent
to the FRB itself. We find that 21 of the remaining 33 FRBs pass
this filter. Those 21 ACF peak spacings were then visually checked
against the timeseries profiles, to ensure that the above methodology
returned results that were consistent with the visual appearance of
the FRB. It should be noted that peaks in an ACF can be difficult
to interpret or assign significances to; for example, for FRBs with
complex quasi-periodic structure, this could be representative of the
distance between the two brightest sub-bursts, or an indication of
evenly-spaced components.
The median and median absolute deviation of the distribution of
ACF-derived timescales is 5.82 ± 1.16 ms. This implies that, while
individual bursts may have preferred periods or spacings, we do not
see a sharp mode or otherwise tightly-clustered distribution providing
evidence of a shared, strict periodicity between sub-bursts across the
sample, which corroborates the report of no 1 ms–1000 s periodicity
from Zhang et al. (2023).
In the future, this sort of technique would be improved by fitting for
the FRB shape, subtracting it from the data, and then fully permuting
the remaining profile, instead of the “bookend” noise-permutation
method described above.
4.3.2 Sub-Burst Periodicity
As noted by Petroff et al. (2022), strict periodicity even within a single
sub-burst (as in CHIME/FRB Collaboration et al. 2022) supports
a magnetospheric origin of FRB emission, given that it is difficult
to produce with an external shock model. Visually, FRB # 10 is a
candidate for this kind of strict periodicity. To assess the statistical
significance of the periodicity in this particular burst, we employ
methodology similar to CHIME/FRB Collaboration et al. (2022), as
follows.
We first check for a peak in the squared Fourier transform, which
we find at 6.4 ms (the ACF peak for this FRB was at 5.7 ms). To
find actual times-of-arrival (ToAs) of each of the four subbursts, we
perform a least-squares fit of a function containing four Gaussians
(each with independent amplitude, width, and central time) and a
constant vertical offset. Using the results of that fit, we extract the
central times as the ToAs; we then re-fit while enforcing a constant
spacing between peaks, letting only period and start time of the first
subburst vary while fixing the amplitudes, widths, and offset to the
MNRAS 000, 1–17 (2023)
12. 12 S. Z. Sheikh et al.
best-fit values from the previous fit. The resulting best-fit period is
6.1 ms.
To assess the significance of this result, we calculate the ˆ
𝐿[𝑛]
statistic from CHIME/FRB Collaboration et al. (2022), a metric of
how well the ToAs approximate the linear relationship expected for
arrival time vs. integer multiples of the best-fit period (where larger
scores equal better approximation). Using the ToAs obtained in the
first 4-Gaussian fit and a 6.1 ms period, we find ˆ
𝐿[𝑛]𝐹𝑅𝐵10 = 3.459.
Then, we simulate 10000 arrays of four ToAs each, with the following
conditions:
(i) Average spacings ¯
𝑑 that would enforce all four pulses falling
within the length of the timeseries
(ii) An “exclusion factor” (minimum spacing factor) of 𝜒 = 0.2
(iii) ToAs drawn from a uniform probability distribution between
𝜒 ¯
𝑑 ≤ 𝑑 ≤ (2 − 𝜒) ¯
𝑑
This creates series of four ToAs that are not drawn from a periodic
distribution, but will have a range of scores in ˆ
𝐿[𝑛] which could,
in cases, approach periodicity. When we compare ˆ
𝐿[𝑛]𝐹𝑅𝐵10 to the
distribution of ˆ
𝐿[𝑛] values from the simulations, we find that it is
larger than 81% of values in the simulation, giving a generous “false
alarm probability” of 19%. From this result, we cannot reject the
null hypothesis of a non-periodic emission mechanism. Note that the
first two sub-pulses are particularly low SNR, so their Gaussian-fitted
ToAs may be contributing to the lower ˆ
𝐿[𝑛] score.
We also see no obvious periodicity between bursts. However, we
note that, because the ATA can only observe the part of the FRB’s
energy distribution that is above both bimodal peaks seen by Zhang
et al. (2023) and Feng et al. (2023), our sampling of periodicity or
patterns in wait-time will be incomplete.
5 DISCUSSION AND CONCLUSION
As described in Section 2.3, we detect 35 bursts from the Fast Radio
Burst (FRB) 20220912A in 541 hours of observation with the Allen
Telescope Array (ATA), using the SPANDAK detection pipeline. The
FRBs appear throughout the 672 MHz bandpass, biased towards the
lower (∼ 1 GHz) frequency end, with an average sub-burst duration
of 1.2 ms and an average sub-burst bandwidth of ∼ 200 MHz. In
Section 3, we used the frbgui package, which leverages 2D fits to
the Auto-Correlation Function (ACF) of the dynamic spectrum of
each bursts, to measure spectrotemporal features from each FRB. In
Section 4, we described the following features in our dataset:
(i) A median dispersion measure of 219.775 pc cm−3 (Section
3.1)
(ii) A median isotropic equivalent burst energy of 1 × 1039 erg
(Section 4.1.1)
(iii) A positive, linear correlation between center frequency and
bandwidth (Section 4.1.2)
(iv) A decrease in center frequency and bandwidth over the two
months of the campaign (Section 4.1.3)
(v) A slight decrease in duration with increasing center frequency
(Section 4.1.5)
(vi) No evidence for scattering (Section 4.1.6)
(vii) FRB 20220912A must have a cut-off fluence 𝐹max ≲ 104 Jy-
ms to be consistent with the all-sky fluence distribution (Section 4.2)
(viii) FRB 20220912A significantly contributed to the all-sky
FRB rate at a level of a few percent for fluences ≳100 Jy-ms (Section
4.2)
(ix) The majority of bursts in the observed sample were multi-
component FRBs, with median component spacings of 5.82±1.16 ms
(Section 4.3.1)
(x) No bursts showed statistically significant sub-burst periodicity
(Section 4.3.2)
Broadly speaking, there are two classes of FRB models depending
on whether the radio bursts are created within the magnetosphere of
a neutron star (or black hole) or far from the magnetosphere.
One of the close-in models is coherent curvature emission, where
charged particles in macroscopic clumps of longitudinal sizes ≲ 𝜆
(the FRB wavelength) radiate coherently when moving along curved
magnetic field lines (e.g., Lu & Kumar 2018; Lu et al. 2020). In this
model, the FRB spectrum is set by the spatial distribution of currents
in the longitudinal direction. By Fourier transformation, a narrow
spectrum of Δ𝜔/𝜔center ≃ 0.3 can be produced by a modestly long
(𝑁 ∼ few) chain of current islands.
One class of the far-away models relies on synchrotron maser
emission when an ultra-relativistic outflow interacts with strongly
magnetized plasma forming a quasi-perpendicular shock (Hoshino
& Arons 1991; Metzger et al. 2019; Plotnikov & Sironi 2019). The
synchrotron maser model predicts Δ𝜔/𝜔center ≳ 1 for two reasons:
(1) the ring-like particle distribution function is not infinitely thin
in phase space but with a fractional momentum spread of order
unity — this allows the rapid growth of modes at a rather broad
range of frequencies Δ𝜔′/𝜔′
center ∼ 1 (here, primes ′ mean in the
comoving frame of the shocked plasma) instead of a narrow spectral
line (Plotnikov & Sironi 2019; Sironi et al. 2021); (2) the Doppler
beaming for viewing angles of ≲ 1/Γ across a quasi-spherical shock
front creates a broad spectrum Δ𝜔/𝜔center ∼ 1 in the observer’s
frame (Metzger et al. 2019; Beniamini & Kumar 2020). Previous
observations show that many bursts, especially those from repeaters
(Pleunis et al. 2021b), have narrow bandwidths Δ𝜔/𝜔center ≪ 1. For
the synchrotron maser model to be viable for these narrow-banded
bursts, external propagation effects (e.g., Cordes et al. 2017; Sobacchi
et al. 2022) must be playing a role at modulating the spectral intensity
across narrow frequency intervals.
While magnetar models are currently favoured, other exotic re-
peater models do exist. For example, superradiance models rely on
a narrowband emitter similar to a molecular maser, and triggered
superradiance models invoke FRBs initiated in the system by a more
distant coherent emitter such as a pulsar (Dicke 1954; Houde et al.
2019).
The conclusions in the list above do not strongly favour or dis-
favour any of the described classes of models, but do provide a
benchmark against which to compare future observations. For exam-
ple, it remains to be shown how (and if possible at all) propagation
effects in the synchrotron maser model would create a linear corre-
lation between the bandwidth and the central frequency as seen in
this work. This same observation, as well as the tentative decrease
in duration with center frequency, is consistent with a narrowband
emission process such as that in the superradiance model (Rajabi
et al. 2020).
Regardless of the model’s location of emission, our results under-
score the conclusions found in Feng et al. (2023) and Zhang et al.
(2023): low-efficiency models (with efficiencies of order 10−4 or
lower) for the emission mechanism are not compatible with the im-
mense energy being released and the high activity rate of this FRB
source, especially given that our sample consists of bursts with a
median energy ∼ 100× that of the previous literature.
All of the published bursts for this source, our 35 included, are
downward-drifting, potentially indicating that downward frequency
MNRAS 000, 1–17 (2023)
13. ATA observations of FRB 20220912A 13
drift is inherent to the emission mechanism; this is a feature consistent
with both close-in and far-away magnetar models.
This work emphasizes the importance of the ATA in FRB science,
given its wide bandwidth recording capabilities and potential to en-
gage in unique modes of observation, for example, a “Fly’s Eye”
strategy covering up to a 389 sq. deg. field-of-view on the sky at
1 GHz (Siemion et al. 2011). As the refurbishment continues, ad-
ditional FRB-relevant features, such as a fast imaging mode will be
re-implemented on the upgraded system (Law & ATA Team 2009).
More observations of the source, especially at higher frequencies
with instruments like the ATA, will help to differentiate between the
various classes of FRB progenitor models.
ACKNOWLEDGEMENTS
The Allen Telescope Array (ATA) refurbishment program and its
ongoing operations have received substantial support from Franklin
Antonio. Additional contributions from Frank Levinson, Greg Pa-
padopoulos, the Breakthrough Listen Initiative and other private
donors have been instrumental in the renewal of the ATA. Break-
through Listen is managed by the Breakthrough Initiatives, sponsored
by the Breakthrough Prize Foundation. The Paul G. Allen Family
Foundation provided major support for the design and construction
of the ATA, alongside contributions from Nathan Myhrvold, Xil-
inx Corporation, Sun Microsystems, and other private donors. The
ATA has also been supported by contributions from the US Naval
Observatory and the US National Science Foundation. S.Z.S. ac-
knowledges that this material is based upon work supported by the
National Science Foundation MPS-Ascend Postdoctoral Research
Fellowship under Grant No. 2138147. Participation of J.K. made
possible by SETI Institute REU program (NSF award #2051007).
The authors would also like to thank Ron Maddalena for his help in
measuring the sensitivity of the ATA feeds. We acknowledge use of
the CHIME/FRB Public Database, provided at https://www.chime-
frb.ca/ by the CHIME/FRB Collaboration. We also acknowledge use
of the software packages pandas (pandas development team 2023),
numpy (Harris et al. 2020), astropy (Astropy Collaboration et al.
2022), and YOUR (Aggarwal et al. 2020).
DATA AVAILABILITY
The extracted FRB properties are available in the article and in
its online supplementary material. The dynamic spectra in archive
or filterbank formats will be shared on reasonable request to the
corresponding author.
REFERENCES
Agarwal D., et al., 2020, arXiv e-prints, p. arXiv:2003.14272
Aggarwal K., et al., 2020, Journal of Open Source Software, 5, 2750
Alstott J., Bullmore E., Plenz D., 2014, PloS one, 9, e85777
Astropy Collaboration et al., 2022, apj, 935, 167
Bailes M., 2022, Science, 378, abj3043
Bannister K. W., et al., 2019, Science, 365, 565
Barsdell B. R., 2012, PhD thesis, Swinburne University of Technology
Bean B., et al., 2022, Publications of the Astronomical Society of the Pacific,
134, 114501
Beniamini P., Kumar P., 2020, MNRAS, 498, 651
Bhusare Y., et al., 2022, The Astronomer’s Telegram, 15806, 1
Bochenek C. D., McKenna D. L., Belov K. V., Kocz J., Kulkarni S. R., Lamb
J., Ravi V., Woody D., 2020, PASP, 132, 034202
Bright J. S., et al., 2023, arXiv preprint arXiv:2303.13583
CHIME/FRB Collaboration et al., 2020a, Nature, 582, 351
CHIME/FRB Collaboration et al., 2020b, Nature, 587, 54
CHIME/FRB Collaboration et al., 2022, Nature, 607, 256
CHIME/FRB Collaboration et al., 2023, ApJ, 947, 83
Chamma M. A., Rajabi F., Kumar A., Houde M., 2023, Monthly Notices of
the Royal Astronomical Society, p. stad1108
Clark M. A., La Plante P. C., Greenhill L. J., 2011, arXiv e-prints, p.
arXiv:1107.4264
Clauset A., Shalizi C. R., Newman M. E., 2009, SIAM review, 51, 661
Cordes J. M., Chatterjee S., 2019, ARA&A, 57, 417
Cordes J. M., Wasserman I., Hessels J. W. T., Lazio T. J. W., Chatterjee S.,
Wharton R. S., 2017, ApJ, 842, 35
Dicke R. H., 1954, Physical Review, 93, 99
Fedorova V. A., Rodin A. E., 2022, The Astronomer’s Telegram, 15713, 1
Feng Y., et al., 2022, The Astronomer’s Telegram, 15723, 1
Feng Y., et al., 2023, arXiv preprint arXiv:2304.14671
Gajjar V., et al., 2018, ApJ, 863, 2
Gajjar V., et al., 2021, AJ, 162, 33
Gajjar V., et al., 2022, ApJ, 932, 81
Gehrels N., 1986, ApJ, 303, 336
Gourdji K., Michilli D., Spitler L. G., Hessels J. W. T., Seymour A., Cordes
J. M., Chatterjee S., 2019, ApJ, 877, L19
Harris C. R., et al., 2020, Nature, 585, 357
Herrmann W., 2022, The Astronomer’s Telegram, 15691, 1
Hessels J. W. T., et al., 2019, ApJ, 876, L23
Hoshino M., Arons J., 1991, Physics of Fluids B, 3, 818
Hotan A. W., van Straten W., Manchester R. N., 2004, Publ. Astron. Soc.
Australia, 21, 302
Houde M., Rajabi F., Gaensler B. M., Mathews A., Tranchant V., 2019,
MNRAS, 482, 5492
Jahns J. N., et al., 2023, MNRAS, 519, 666
James C. W., Prochaska J. X., Macquart J. P., North-Hickey F. O., Bannister
K. W., Dunning A., 2022, MNRAS, 509, 4775
Kirsten F., et al., 2022, The Astronomer’s Telegram, 15727, 1
Kumar P., Shannon R. M., Lower M. E., Bhandari S., Deller A. T., Flynn C.,
Keane E. F., 2022, Monthly Notices of the Royal Astronomical Society,
512, 3400
Kumar P., et al., 2023, arXiv preprint arXiv:2304.01763
Law C. J., ATA Team 2009, in American Astronomical Society Meeting
Abstracts #214. p. 601.05
Law C. J., et al., 2017, ApJ, 850, 76
Li D., et al., 2021, Nature, 598, 267
Lu W., Kumar P., 2018, MNRAS, 477, 2470
Lu W., Piro A. L., 2019, ApJ, 883, 40
Lu W., Kumar P., Zhang B., 2020, MNRAS, 498, 1397
Luo R., Lee K., Lorimer D. R., Zhang B., 2018, MNRAS, 481, 2320
MacKinnon J. G., White H., 1985, Journal of econometrics, 29, 305
Macquart J. P., Ekers R., 2018, MNRAS, 480, 4211
Majid W. A., Pearlman A. B., Nimmo K., Hessels J. W. T., Prince T. A.,
Naudet C. J., Kocz J., Horiuchi S., 2020, ApJ, 897, L4
Majid W. A., et al., 2021, ApJ, 919, L6
Marcote B., et al., 2020, Nature, 577, 190
McKinven R., CHIME/FRB Collaboration 2022, The Astronomer’s Tele-
gram, 15679, 1
Metzger B. D., Margalit B., Sironi L., 2019, MNRAS, 485, 4091
Michilli D., et al., 2018, Nature, 553, 182
Nimmo K., et al., 2022, Nature Astronomy, 6, 393
Pastor-Marazuela I., et al., 2021, Nature, 596, 505
Pearlman A. B., Majid W. A., Prince T. A., Nimmo K., Hessels J. W., Naudet
C. J., Kocz J., 2020, The Astrophysical Journal Letters, 905, L27
Perera B., et al., 2022, The Astronomer’s Telegram, 15734, 1
Perley R. A., Butler B. J., 2017, The Astrophysical Journal Supplement Series,
230, 7
Petroff E., Hessels J., Lorimer D., 2022, The Astronomy and Astrophysics
Review, 30, 2
Pilia M., et al., 2020, arXiv e-prints, p. arXiv:2003.12748
Planck Collaboration et al., 2016, A&A, 594, A13
MNRAS 000, 1–17 (2023)
14. 14 S. Z. Sheikh et al.
Platts E., et al., 2021, MNRAS, 505, 3041
Pleunis Z., et al., 2021a, The Astrophysical Journal Letters, 911, L3
Pleunis Z., et al., 2021b, ApJ, 923, 1
Plotnikov I., Sironi L., 2019, MNRAS, 485, 3816
Rajabi F., Chamma M. A., Wyenberg C. M., Mathews A., Houde M., 2020,
Monthly Notices of the Royal Astronomical Society, 498, 4936
Rajwade K., et al., 2022, The Astronomer’s Telegram, 15791, 1
Ravi V., 2022, The Astronomer’s Telegram, 15716, 1
Ravi V., DSA-110 Collaboration 2023, in American Astronomical Society
Meeting Abstracts. p. 239.01
Ravi V., et al., 2022, arXiv e-prints, p. arXiv:2211.09049
Ryder S. D., et al., 2022, arXiv e-prints, p. arXiv:2210.04680
Sand K. R., et al., 2022, ApJ, 932, 98
Savitzky A., Golay M. J., 1964, Analytical chemistry, 36, 1627
Scholz P., et al., 2016, ApJ, 833, 177
Shannon R. M., et al., 2018, Nature, 562, 386
Sheikh S., et al., 2022, The Astronomer’s Telegram, 15735, 1
Shin K., et al., 2023, ApJ, 944, 105
Siemion A. P., et al., 2011, The Astrophysical Journal, 744, 109
Sironi L., Plotnikov I., Nättilä J., Beloborodov A. M., 2021, Phys. Rev. Lett.,
127, 035101
Sobacchi E., Lyubarsky Y., Beloborodov A. M., Sironi L., 2022, MNRAS,
511, 4766
Spitler L. G., et al., 2016, Nature, 531, 202
Wang W.-Y., Yang Y.-P., Niu C.-H., Xu R., Zhang B., 2022, ApJ, 927, 105
Welch J., et al., 2009, IEEE Proceedings, 97, 1438
Zhang B., 2020, Nature, 587, 45
Zhang Y. G., Gajjar V., Foster G., Siemion A., Cordes J., Law C., Wang Y.,
2018, ApJ, 866, 149
Zhang Y.-K., et al., 2023, arXiv preprint arXiv:2304.14665
Zhou D. J., et al., 2022, Research in Astronomy and Astrophysics, 22, 124001
pandas development team T., 2023, pandas-dev/pandas: Pandas,
doi:10.5281/zenodo.7794821, https://doi.org/10.5281/zenodo.
7794821
van Straten W., Bailes M., 2011, Publ. Astron. Soc. Australia, 28, 1
MNRAS 000, 1–17 (2023)