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Sérgio Sacani

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Wepresent Atacama Large Millimeter/submillimeter Array 12-m, 7-m, and Total Power Array observations of the FUOrionis outbursting system, covering spatial scales ranging from 160 to 25,000 au. The high-resolution interferometric data reveal an elongated 12CO(2–1) feature previously observed at lower resolution in 12CO(3–2). Kinematic modeling indicates that this feature can be interpreted as an accretion streamer feeding the binary system. The mass infall rate provided by the streamer is significantly lower than the typical stellar accretion rates (even in quiescent states), suggesting that this streamer alone is not massive enough to sustain the enhanced accretion rates characteristic of the outbursting class prototype. The observed streamer may not be directly linked to the current outburst, but rather a remnant of a previous, more massive streamer that may have contributed enough to the disk mass to render it unstable and trigger the FU Orionis outburst. The new data detect, for the first time, a vast, slow-moving carbon monoxide molecular outflow emerging from this object. To accurately assess the outflow properties (mass, momentum, and kinetic energy), we employ 13CO(2–1) data to correct for optical depth effects. The analysis indicates that the outflow corresponds to swept-up material not associated with the current outburst, similar to the slow molecular outflows observed around other FUor and Class I protostellar objects.

Discovery of an Accretion Streamer and a Slow Wide-angle Outflow around FUOri...

Sérgio Sacani

We explore different scenarios to explain the chemical difference found in the remarkable giant-giant binary system HD138202+CD−3012303. For the first time, we suggest how to distinguish these scenarios by taking advantage of the extensive convective envelopes of giant stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying a full line-by-line differential analysis on GHOST high-resolution spectra. We used the FUNDPAR program with ATLAS12 model atmospheres and specific opacities calculated for an arbitrary composition through a doubly iterated method. Physical parameters were estimated with the isochrones package and evolutionary tracks were calculated via MIST models. Results. We found a significant chemical difference between the two stars (∆[Fe/H]∼0.08dex), which is largely unexpected considering the insensitivity of giant stars to planetary ingestion and diffusion effects. We tested the possibility of engulfment events by using several different combinations of stellar mass, ingested mass, metallicity of the engulfed object and different convective envelopes. However, the planetary ingestion scenario does not seem to explain the observed differences. For the first time, we distinguished the source of chemical differences using a giant-giant binary system. By ruling out other possible scenarios such as planet formation and evolutionary effects between the two stars, we suggest that primordial inhomogeneities might explain the observed differences. This remarkable result implies that the metallicity differences that were observed in at least some main-sequence binary systems might be related to primordial inhomogeneities rather than engulfment events. We also discuss the important implications of finding primordial inhomogeneities, which affect chemical tagging and other fields such as planet formation. We strongly encourage the use of giantgiant pairs. They are a relevant complement to main-sequence pairs for determining the origin of the observed chemical differences in multiple systems.

Disentangling the origin of chemical differences using GHOST

Sérgio Sacani

On 26 January 2023, a military pilot reported four potential unidentified anomalous phenomena (UAP) while operating in the Eglin Air Force Base training range off the coast of Florida. Through the onboard radar system, the pilot initially observed that the four objects were aloft between 16,000 – 18,000 feet and appeared to be flying in formation. However the pilot observed only one of the four objects visually and captured two images of the single object via the aircraft’s electro-optical/infrared (EO/IR) sensor (see Figures 1A and 1B). The pilot could not record video of the event because the aircraft’s video recording equipment was inoperable prior to and during the aircraft’s flight. The pilot observed this single object aloft at 16,000 feet. The following case information is based on the pilot’s initial report and a subsequent discussion that AARO held with the pilot to seek additional details about the pilot’s observation of the reported object.

All-domain Anomaly Resolution Office U.S. Department of Defense (U) Case: “Eg...

Sérgio Sacani

RecoveringancientrecordsofEarth'smagneticfieldisessentialfordeterminingtheroleofthemagnetosphereinprotectingearlyEarthfromcosmicradiationandatmosphericescape.WepresentpaleomagneticfieldtestshintingthatarecordofEarth's3.7‐billion‐year(Ga)oldmagneticfieldmaybepreservedinthenortheasternIsuaSupracrustalBeltasachemicalremanentmagnetizationacquiredduringamphibolite‐grademetamorphisminthebandedironformation.MultiplepetrologicalandgeochronologicallinesofevidenceindicatethatthenorthernmostpartofIsuahasnotexperiencedmetamorphictemperaturesexceeding380°CsincetheEoarchean,suggestingtherockshavenotbeensignificantlyheatedsincemagnetizationwasacquired.Weuse“pseudo”bakedcontacttests(intrusionsemplaced3.26–3.5Gaago)andafoldtest(folding3.6Gaago)todemonstratethatsomesamplespreserveaca.3.7Garecordofthemagneticfield.Werecoverafieldstrengthof>15μT.ThissuggeststhatEarth'smagneticfieldmayhavebeenweakenoughtoenhanceatmosphericescapeduringtheArchean

PossibleEoarcheanRecordsoftheGeomagneticFieldPreservedintheIsuaSupracrustalBe...

Sérgio Sacani

Jupiter’s moon Io hosts extensive volcanism, driven by tidal heating. The isotopic composition of Io's inventory of volatile chemical elements, including sulfur and chlorine, reflects its outgassing and mass loss history, and thus records information about its evolution. We used millimeter observations of Io’s atmosphere to measure sulfur isotopes in gaseous SO2 and SO, and chlorine isotopes in gaseous NaCl and KCl. We find 34S/32S = 0.0595 ± 0.0038 (equivalent to δ34S = +347 ± 86‰), which is highly enriched compared to average Solar System values and indicates that Io has lost 94 to 99% of its available sulfur. Our measurement of 37Cl/35Cl = 0.403 ± 0.028 (δ37Cl = +263 ± 88‰) shows that chlorine is similarly enriched. These results indicate that Io has been volcanically active for most (or all) of its history, with potentially higher outgassing and mass-loss rates at earlier times.

Isotopic evidence of long-lived volcanism on Io

Sérgio Sacani

Context. Determining the size distribution of asteroids is key to understanding the collisional history and evolution of the inner Solar System. Aims. We aim to improve our knowledge of the size distribution of small asteroids in the main belt by determining the parallaxes of newly detected asteroids in the Hubble Space Telescope (HST) archive and subsequently their absolute magnitudes and sizes. Methods. Asteroids appear as curved trails in HST images because of the parallax induced by the fast orbital motion of the spacecraft. Taking into account the trajectory of this latter, the parallax effect can be computed to obtain the distance to the asteroids by fitting simulated trajectories to the observed trails. Using distance, we can obtain the absolute magnitude of an object and an estimation of its size assuming an albedo value, along with some boundaries for its orbital parameters. Results. In this work, we analyse a set of 632 serendipitously imaged asteroids found in the ESA HST archive. Images were captured with the ACS/WFC and WFC3/UVIS instruments. A machine learning algorithm (trained with the results of a citizen science project) was used to detect objects in these images as part of a previous study. Our raw data consist of 1031 asteroid trails from unknown objects, not matching any entries in the Minor Planet Center (MPC) database using their coordinates and imaging time. We also found 670 trails from known objects (objects featuring matching entries in the MPC). After an accuracy assessment and filtering process, our analysed HST asteroid set consists of 454 unknown objects and 178 known objects. We obtain a sample dominated by potential main belt objects featuring absolute magnitudes (H) mostly between 15 and 22 mag. The absolute magnitude cumulative distribution logN(H > H0) ∝ αlog(H0) confirms the previously reported slope change for 15 < H < 18, from α ≈ 0.56 to α ≈ 0.26, maintained in our case down to absolute magnitudes of around H ≈ 20, and therefore expanding the previous result by approximately two magnitudes. Conclusions. HST archival observations can be used as an asteroid survey because the telescope pointings are statistically randomly oriented in the sky and cover long periods of time. They allow us to expand the current best samples of astronomical objects at no extra cost in regard to telescope time.

Hubble Asteroid Hunter III. Physical properties of newly found asteroids

Sérgio Sacani

Massive stars (those ≥8 solar masses at birth) have radiative envelopes that cannot sustain the dynamos that produce magnetic fields in lower mass stars. Despite this, ∼7% of massive stars have observed magnetic fields. We use multi-epoch interferometric and spectroscopic observations to characterise a magnetic binary system formed of two massive stars. We find that only one star of the binary is magnetic. Using the non-magnetic star as an independent reference clock to estimate the age of the system, we show that the magnetic star appears younger than its companion. The system properties, and a surrounding bipolar nebula, can be reproduced by a model in which this system was originally a triple within which two of the stars merged, producing the magnetic massive star. Thus, our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.

Observational constraints on mergers creating magnetism in massive stars

Sérgio Sacani

We report the observation of a coalescing compact binary with component masses 2.5–4.5 M⊙ and 1.2–2.0 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529 181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We estimate a merger rate density of 55+127 −47 Gpc−3yr−1 for compact binary coalescences with properties similar to the source of GW230529 181500; assuming that the source is a neutron star–black hole merger, GW230529 181500-like sources constitute about 60% of the total merger rate inferred for neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.

Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M⊙ Compa...

Sérgio Sacani

We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.

The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...

Sérgio Sacani

The evolved stages of massive stars are poorly understood, but invaluable constraints can be derived from spatially resolved observations of nearby red supergiants, such as Betelgeuse. Atacama Large Millimeter/submillimeter Array (ALMA) observations of Betelgeuse showing a dipolar velocity field have been interpreted as evidence for a projected rotation rate of about 5 km s−1. This is 2 orders of magnitude larger than predicted by single-star evolution, which led to suggestions that Betelgeuse is a binary merger. We propose instead that large-scale convective motions can mimic rotation, especially if they are only partially resolved. We support this claim with 3D CO5BOLDsimulations of nonrotating red supergiants that we postprocessed to predict ALMA images and SiO spectra. We show that our synthetic radial velocity maps have a 90% chance of being falsely interpreted as evidence for a projected rotation rate of 2 km s−1 or larger for our fiducial simulation. We conclude that we need at least another ALMA observation to firmly establish whether Betelgeuse is indeed rapidly rotating. Such observations would also provide insight into the role of angular momentum and binary interaction in the late evolutionary stages. The data will further probe the structure and complex physical processes in the atmospheres of red supergiants, which are immediate progenitors of supernovae and are believed to be essential in the formation of gravitational-wave sources.

Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Con...

Sérgio Sacani

We present a comprehensive analysis aimed at proving the hypothesis that a train of small-scale features observed by the Wide-field Imager (WISPR) onboard the Parker Solar Probe (PSP) are the signature of a Kelvin–Helmholtz instability (KHI). These features were seen near the flank of a Coronal Mass Ejection (CME) wake between 7.5 Re and 9.5Re, lasting for about 30 minutes. The CME was a slow event, associated with a streamer blowout. We analyzed the size of the eddies and found growth during their evolution while maintaining separation distances and alignment typical of Kelvin–Helmholtz vortexes. We then assessed the magnetic field conditions that would make the observation of such an instability plausible. Two methods were used to cross-check our findings. The measured thickness of the boundary layer supports KHI candidacy, and the estimated linear growth rate suggests nonlinear saturation within the expected timescale. We conclude that a KHI is a plausible explanation for the observed features, and therefore that such instabilities might exist in the low and middle solar corona (within ∼15 Re) and can be detected in white light observations. Their observation, however, might be rare due to stringent conditions like the observer’s proximity, suitable viewing circumstances, magnetic field topology, and flow properties. This study highlights the unique capability of PSP/WISPR in observing such phenomena, especially as PSP perihelia reach closer distances to the Sun.

First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

Sérgio Sacani

Rapidly rotating fluids have a rotation profile that depends only on the distance from the rotation axis, in accor-dance with the Taylor- Proudman theorem. Although the Sun was expected to be such a body, helioseismology showed that the rotation rate in the convection zone is closer to constant on radii. It has been postulated that this deviation is due to the poles being warmer than the equator by a few degrees. Using numerical simulations, we show that the pole- to-equator temperature difference cannot exceed 7 kelvin as a result of the back- reaction of the high- latitude baroclinically unstable inertial modes. The observed amplitudes of the modes further indicate that this maximum temperature difference is reached in the Sun. We conclude that the Sun’s latitudinal differential rotation reaches its maximum allowed value

The Sun’s differential rotation is controlled by high- latitude baroclinicall...

Sérgio Sacani

We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.

Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGN

Sérgio Sacani

Titã, que é a maior lua de Saturno e envolta em mistério, possui uma atmosfera densa repleta de vários compostos orgânicos, alguns dos quais poderiam servir como indicadores de vida se fossem encontrados em nosso próprio planeta. Surge a questão intrigante sobre os mecanismos subjacentes à formação desses compostos em Titã e se eles são a chave para desvendar os mistérios que cercam as origens da vida na Terra, o que leva a uma busca por respostas que entrelaçam os dois corpos celestes. A sonda Huygens da Agência Espacial Européia (ESA), que fez sua chegada histórica a Titã no ano de 2005, é um instrumento fundamental pronto para esclarecer esses processos enigmáticos. Ao mesmo tempo, observatórios terrestres equipados com capacidades telescópicas avançadas contribuem significativamente para esse empreendimento científico, auxiliando no planejamento estratégico para determinar o local preciso de pouso da Huygens, contemplando a dicotomia entre solo sólido e um oceano envolto em metano como possíveis zonas de pouso.

Huygens - Exploring Titan A Mysterious World

Sérgio Sacani

Our Sun lies within 300 parsecs of the 2.7-kiloparsecs-long sinusoidal chain of dense gas clouds known as the Radclife Wave1 . The structure’s wave-like shape was discovered using three-dimensional dust mapping, but initial kinematic searches for oscillatory motion were inconclusive2–7 . Here we present evidence that the Radclife Wave is oscillating through the Galactic plane while also drifting radially away from the Galactic Centre. We use measurements of line-of-sight velocity8 for 12CO and threedimensional velocities of young stellar clusters to show that the most massive star-forming regions spatially associated with the Radclife Wave (including Orion, Cepheus, North America and Cygnus X) move as though they are part of an oscillating wave driven by the gravitational acceleration of the Galactic potential. By treating the Radclife Wave as a coherently oscillating structure, we can derive its motion independently of the local Galactic mass distribution, and directly measure local properties of the Galactic potential as well as the Sun’s vertical oscillation period. In addition, the measured drift of the Radclife Wave radially outwards from the Galactic Centre suggests that the cluster whose supernovae ultimately created today’s expanding Local Bubble9 may have been born in the Radclife Wave.

The Radcliffe Wave Of Milk Way is oscillating

Sérgio Sacani

Relativistic jets are observed from accreting and cataclysmic transients throughout the Universe, and have a profound impact on their surroundings1,2 . Despite their importance, their launch mechanism is not known. For accreting neutron stars, the speed of their compact jets can reveal whether the jets are powered by magnetic felds anchored in the accretion fow3 or in the star itself 4,5 , but so far no such measurements exist. These objects can show bright explosions on their surface due to unstable thermonuclear burning of recently accreted material, called type-I X-ray bursts6 , during which the mass-accretion rate increases7–9 . Here, we report on bright fares in the jet emission for a few minutes after each X-ray burst, attributed to the increased accretion rate. With these fares, we measure the speed of a neutron star compact jet to be v c = 0.38−0.08 +0.11 , much slower than those from black holes at similar luminosities. This discovery provides a powerful new tool in which we can determine the role that individual system properties have on the jet speed, revealing the dominant jet launching mechanism.

Thermonuclear explosions on neutron stars reveal the speed of their jets

Sérgio Sacani

Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures, their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential. Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm applied on the WHL (Wen–Han–Liu) cluster catalog within a redshift range of 0.05 z 0.42. We name the most massive supercluster at z ∼ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is ∼5.8 × 10 15 Me and the median size ∼65 Mpc. We find that the supercluster environment slightly affects the growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its maximum extent with a power-law index, α ∼ −2. The phase-space distribution of mock superclusters shows that, on average, ∼90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock halos’ average number density and peculiar velocity profiles in and around the superclusters.

Identification of Superclusters and Their Properties in the Sloan Digital Sky...

Sérgio Sacani

Dedicated scientific measurements of the strength and direction of the Earth's magnetic field began at Greenwich and Kew observatories in London, United Kingdom, in the middle of the nineteenth century. Using advanced techniques for the time, collimated light was focussed onto mirrors mounted on free-swinging magnetized needles which reflected onto photographic paper, allowing continuous analog magnetograms to be recorded. By good fortune, both observatories were in full operation during the so-called Carrington storm in early September 1859 and its precursor storm in late August 1859. Based on digital images of the magnetograms and information from the observatory yearbooks and scientific papers, it is possible to scale the measurements to International System of Units (SI units) and extract quasi-minute cadence spot values. However, due to the magnitude of the storms, the periods of the greatest magnetic field variation were lost as the traces moved off-page. We present the most complete digitized magnetic records to date of the 10-day period from 25 August to 5 September 1859 encompassing the Carrington storm and its lesser recognized precursor on 28 August. We demonstrate the good correlation between observatories and estimate the instantaneous rate of change of the magnetic field.

Digitized Continuous Magnetic Recordings for the August/September 1859 Storms...

Sérgio Sacani

Using Gaia Data Release 3 astrometry and spectroscopy, we study two new substructures in the orbit–metallicity space of the inner Milky Way: Shakti and Shiva. They were identified as two confined, high-contrast overdensities in the (Lz, E) distribution of bright (G < 16) and metal-poor (−2.5<[M/H]<−1.0) stars. Both have stellar masses of Må107Me, and are distributed on prograde orbits inside the solar circle in the Galaxy. Both structures have an orbit-space distribution that points toward an accreted origin; however, their abundance patterns—from APOGEE—are such that are conventionally attributed to an in situ population. These seemingly contradictory diagnostics could be reconciled if we interpret the abundances [Mg/Fe], [Al/Fe], [Mg/Mn] versus [Fe/H] distribution of their member stars merely as a sign of rapid enrichment. This would then suggest one of two scenarios. Either these prograde substructures were created by some form of resonant orbit trapping of the field stars by the rotating bar; a plausible scenario proposed by Dillamore et al. Or, Shakti and Shiva were protogalactic fragments that formed stars rapidly and coalesced early, akin to the constituents of the poor old heart of the Milky Way, just less deep in the Galactic potential and still discernible in orbit space.

Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way

Sérgio Sacani

The Milky Way dwarf spheroidal satellite galaxies (dSphs) are particularly intriguing targets to search for gamma rays from Weakly Interacting Massive Particle (WIMP) dark matter (DM) annihilation or decay. They are nearby, DM-dominated, and lack significant emission from standard astrophysical processes. Previous studies using the Fermi-Large Area Telescope (LAT) of DMinduced emission from dSphs have provided the most robust and stringent constraints on the DM annihilation cross section and mass. We report here an analysis of the Milky Way dSphs using over 14 years of LAT data along with an updated census of dSphs and J-factor estimates. While no individual dSphs are significantly detected, we do find slight excesses with respect to background at the ≳ 2σ local significance level in both tested annihilation channels (b¯ b, τ+τ−) for seven of the dSphs. We do not find a significant DM signal from the combined likelihood analysis of the dSphs (sglobal ∼ 0.5σ), yet a marginal local excess relative to background at a 2−3σ level is observed at a DMmass of Mχ = 150−230 GeV (Mχ = 30−50 GeV) for DM annihilation into b¯ b (τ+τ−). Given the lack of a significant detection, we place updated constraints on the b¯ b and τ+τ− annihilation channels that are generally consistent with previous recent results. As in past studies, tension is found with some WIMP DM interpretations of the Galactic Center Excess (GCE), though the limits are consistent with other interpretations given the uncertainties of the Galactic DM density profile and GCE systematics. Based on conservative assumptions of improved sensitivity with increased Fermi-LAT exposure time and moderate increases in the sample of Milky Way dSphs, we project that the local ∼ 2σ signal, if real, could approach the ∼ 4σ local confidence level with additional ∼10 years of observation.

Legacy Analysis of Dark Matter Annihilation from the Milky Way Dwarf Spheroid...

Sérgio Sacani

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