The standard paradigm of hierarchical structure formation in a LambdaCDM universe predicts the presence of dark matter subhaloes, hosted by Milky Way-sized galaxies. Anticipated subhalo masses range from 10^{10} down to a cut-off mass between 10^{-3} and 10^{-11} solar masses. If dark matter is composed of heavy self-annihilating or decaying particles, these subhaloes could be visible in the gamma-ray band as faint and temporally constant sources without astrophysical counterparts. Based upon realistic subhalo models and current observational constraints on annihilating dark matter scenarios, we predict that one massive Galactic subhalo between 10^6 and 10^8 solar masses may already be present in the 11-month catalogue of Fermi-LAT. Indeed, at least twelve objects in the first Fermi catalogue qualify as candidates. The most promising object, 1FGL J0030.7+0724, is investigated in detail using a dedicated Swift X-ray follow-up observation and a refined positional analysis of the 24-month Fermi-LAT data. With the new observations, seven point-like X-ray sources have been discovered, of which SWIFT J003119.8+072454, which coincides with a faint radio source (12 mJy at 1.4 GHz), serves as a counterpart candidate of 1FGL J0030.7+0724. The broad-band spectral energy distribution is consistent with a high-energy-peaked blazar. However, flux and extent of 1FGL J0030.7+0724 may also be compatible with a dark matter subhalo. Detection of temporal variability or improved astrometry of 1FGL J0030.7+0724 are necessary to rule out or confirm an astrophysical origin. We discuss strategies to identify gamma-ray sources that are associated with self-annihilating dark matter subhaloes.
Dark matter annihilation signals coming from Galactic subhaloes may account for a small fraction of unassociated point sources detected in the Second Fermi-LAT catalogue (2FGL). To investigate this possibility, we present Sibyl, a Random Forest classifier that offers predictions on class memberships for unassociated Fermi-LAT sources at high Galactic latitudes using gamma-ray features extracted from the 2FGL. Sibyl generates a large ensemble of classification trees that are trained to vote on whether a particular object is an active galactic nucleus (AGN) or a pulsar. After training on a list …
Searches for "dark" subhaloes in gamma-ray point-like source catalogues are among promising strategies for indirect dark matter detection. Such a search is nevertheless affected by uncertainties related, on the one hand, to the modelling of the dark matter subhalo distribution in Milky-Way-like galaxies, and, on the other hand, to the sensitivity of gamma-ray instruments to the dark matter subhalo signals. In the present work, we assess the detectability of dark matter subhaloes in Fermi-LAT catalogues, taking into accounts uncertainties associated with the modelling of the Galactic subhalo po…
The presence of substructures in dark matter haloes is an unavoidable consequence of the cold dark matter paradigm. Indirect signals from these objects have been extensively searched for with cosmic rays and gamma-rays. At first sight, Cherenkov telescopes seem not very well suited for such searches, due to their small fields of view and the random nature of the possible dark matter substructure positions in the sky. However, with long enough exposure and an adequate observation strategy, the very good sensitivity of this experimental technique allows us to constrain particle dark matter model…
The first Fermi Large Area Telescope (LAT) catalogue of sources (1FHL) emitting at high energies (above 10 GeV) reports the details of 514 objects detected in the first three years of the Fermi mission. Of these, 71 were reported as unidentified in the 1FHL catalogue, although six are likely to be associated with a supernova remnant (SNR), a Pulsar Wind Nebula (PWN) or a combination of both, thereby leaving a list of 65 still unassociated objects. Herein, we report a preliminary analysis on this sample of objects concentrating on nine 1FHL sources, which were found to have a clear optical extr…
There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area Telescope First Source Catalogue. The point source location accuracy of typically a few arcminutes has allowed the counterparts for many of these sources to be found at other wavelengths, but even so there are 630 which are described as having no plausible counterpart at 80% confidence. In order to help identify the unknown objects, we have cross-correlated the positions of these sources with the Rosat All Sky Survey Bright Source Catalogue. In this way, for Fermi sources which have a possible counterpart in soft X-ra…
In the recently published 3FGL catalogue, the Fermi/LAT collaboration reports the detection of $γ$-ray emission from 3034 sources obtained after four years of observations. The nature of 1010 of those sources is unknown, whereas 2023 have well-identified counterparts in other wavelengths. Most of the associated sources are labelled as blazars (1717/2023), but the BL Lacs or FSRQ nature of 573 of these blazars is still undetermined. The aim of this study was two-fold. First, to significantly increase the number of blazar candidates from a search among the large number of Fermi/LAT 3FGL unassoci…
We describe a catalogue of gamma-ray source candidates, selected using the Minimum Spanning Tree (MST) algorithm on the 9-years Fermi-LAT sky (Pass 8) at energies higher than 10 GeV. The extragalactic sky at absolute Galactic latitudes above 20 degrees has been investigated using rather restrictive selection criteria, resulting in a total sample of 1342 sources. Of these, 249 are new detections, not previously associated with gamma-ray catalogues. A large fraction of them have interesting counterparts, most likely blazars. In this paper the main results on the catalogue selection and search of…
We present an updated version catalogue of gamma-ray source candidates, 12Y-MST, selected using the minimum spanning tree (MST) algorithm on the 12-year Fermi-LAT sky (Pass 8) at energies higher than 10 GeV. The high-energy sky at absolute Galactic latitudes above 20 degrees has been investigated using rather restrictive selection criteria, resulting in a total sample of 1664 photon clusters, or candidate sources. Of these, 230 are new detections, that is, candidate sources without any association in other gamma-ray catalogues. A large fraction of them have interesting counterparts, most likel…
We present the Living Swift-XRT Point Source catalogue (LSXPS) and real-time transient detector. This system allows us for the first time to carry out low-latency searches for new transient X-ray events fainter than those available to the current generation of wide-field imagers, and report their detection in near real-time. Previously, such events could only be found in delayed searches, e.g. of archival data; our low-latency analysis now enables rapid and ongoing follow up of these events, enabling the probing of timescales previously inaccessible. The LSXPS is, uniquely among X-ray catalogu…
Revealing the nature of unassociated high-energy (> 100 MeV) gamma-ray sources remains a challenge 35 years after their discovery. Of the 934 gamma-ray sources at high Galactic latitude (|b| > 15 degrees) in the First Fermi-LAT catalogue (1FGL), 316 have no obvious associations at other wavelengths. In this paper, we apply the K-means unsupervised classification algorithm to isolate potential counterparts for 18 unassociated Fermi sources contained within a 3000 square degree `overlap region' of the sky intensively covered in radio and optical wavelengths. Combining our results with previous w…
High synchrotron peaked blazars (HSPs or HBLs) play a central role in very high energy (VHE) gamma-ray astronomy, and likely in neutrino astronomy. Currently, the largest compilation of HSP blazars, the 2WHSP sample, includes 1691 sources, but it is not complete neither in the radio nor in the X-ray band. In order to provide a more sizable and more accurate set of HSP blazars that is useful for future statistical studies and to plan for VHE/TeV observations, we present the largest sample of extreme and high synchrotron peaked (EHSP;HSP) blazars and blazar candidates: the 3HSP catalogue. The 3H…
We present the second ROSAT all-sky survey source catalogue, hereafter referred to as the 2RXS catalogue. This is the second publicly released ROSAT catalogue of point-like sources obtained from the ROSAT all-sky survey (RASS) observations performed with the PSPC between June 1990 and August 1991, and is an extended and revised version of the bright and faint source catalogues. We used the latest version of the RASS processing to produce overlapping X-ray images of 6.4x6.4 degrees sky regions. To create a source catalogue, a likelihood-based detection algorithm was applied to these, which acco…
Binary star systems represent a significant proportion of the Galactic stellar population, with X-ray binaries being an important subset of these for high energy astrophysics. Although hundreds of X-ray binaries are detected in the Milky Way and beyond, only 12 of these systems are listed in the 4FGL-DR2, the latest Fermi-LAT point source catalogue. With such a small number detectable by Fermi-LAT, much is still unknown about the mechanisms by which these systems emit $γ$-rays. We present the method and current status of our large-scale survey of the X-ray binary population using over 12 years…
We revisit the well-studied outburst of the low mass X-ray binary (LMXB) system V404 Cygni, and claims of gamma-ray excesses observed with the Fermi-LAT instrument. Upon analysing an 11.5 year dataset with the 8-year LAT point source catalogue and 8-year background models, we find no evidence to suggest that there is high energy gamma-ray emission during the outburst period (or at any other time) from V404 Cygni. This is due to the proximity of V404 Cygni to the gamma-ray emitting blazar B2023+336, a luminous source approximately 0.3 degrees away, which causes source confusion at the position …
The high-frequency radio sky, like the gamma-ray sky surveyed by the Fermi satellite, is dominated by flat spectrum radio quasars and BL Lac objects at bright flux levels. To investigate the relationship between radio and gamma-ray emission in extragalactic sources, we have cross-matched the Australia Telescope 20 GHz survey catalog (AT20G) with the Fermi-LAT 1 year Point Source Catalog (1FGL). The 6.0 sr of sky covered by both catalogs (δ < 0\circ, |b| > 1.\circ 5) contains 5890 AT20G radio sources and 604 1FGL gamma-ray sources. The AT20G source positions are accurate to within ~1 arcsec and…
BL Lac Objects (BL Lacs) and Flat Spectrum Radio Quasars (FSRQs) are radio-loud active galaxies (AGNs) whose jets are seen at a small viewing angle (blazars), while Misaligned Active Galactic Nuclei (MAGNs) are mainly radiogalaxies of type FRI or FRII and Steep Spectrum Radio Quasars (SSRQs), which show jets of radiation oriented away from the observer's line of sight. MAGNs are very numerous and well studied in the lower energies of the electromagnetic spectrum but are not commonly observed in the gamma-ray energy range, because their inclination leads to the loss of relativistic boosting of …
We search for gamma-ray emission from 114 Galactic high mass X-ray binaries, including 4 well studied catalogued sources, in 12.5 years of Fermi-LAT data in conjunction with the 10-year point source catalogue. Where a gamma-ray excess appears to be spatially coincident with an X-ray binary, further investigation is performed to ascertain whether this excess is the product of physical processes within the binary system itself. We identify gamma-ray excesses coincident with 20 high mass X-ray binaries where there is little or no prior evidence for gamma-ray emission. However, we find that many o…
Harnessing the XMM-Newton data: X-ray spectral modelling of 4XMM-DR11 detections and 4XMM-DR11s sources
INAF–Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；Department of Physics, University of Helsinki（赫尔辛基大学物理系）；Instituto de Física de Cantabria (CSIC-Universidad de Cantabria)（坎塔布里亚物理研究所（西班牙科学研究中心-坎塔布里亚大学））；Juelich Supercomputing Centre, Forschungszentrum Juelich GmbH（于利希超级计算中心，于利希研究中心有限公司）；Université Paris Saclay and Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学和巴黎西岱大学，法国原子能和替代能源委员会，法国国家科学研究中心，天体物理学与分子生物学研究所）；Institute for Astronomy Astrophysics Space Applications and Remote Sensing (IAASARS), National Observatory of Athens（雅典国立天文台天文学、天体物理学、空间应用和遥感研究所）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理学研究所）
Max-Planck-Institut für Kernphysik（马克斯·普朗克核物理研究所）；Friedrich-Alexander-Universität Erlangen-Nürnberg（埃尔兰根-纽伦堡弗里德里希·阿列克山大大学）；Stockholm University（斯德哥尔摩大学）；The Oskar Klein Centre for Cosmoparticle Physics（奥斯卡·克莱因宇宙粒子物理中心）；Cherenkov Telescope Array Observatory, Science Data Management Centre (SDMC)（切伦科夫望远镜阵列观测站科学数据管理中心）
We present a list of 24 new blazar candidates selected in a search for possible counterparts of spatial clusters of gamma-ray photons in the recent 9Y-MST catalogue, at energies higher than 10 GeV and at Galactic latitudes higher than 20 degrees. 13 of these clusters are also included the preliminary release of the 4FGL catalogue of gamma-ray sources. The search for possible counterparts is based on the possible associations of the clusters with radio sources within a circle having a radius of 6 arcmin. We then investigated the possible optical or mid-IR associations of these sources, checking…
We present the final release of the multi-wavelength XMM-LSS data set,covering the full survey area of 11.1 square degrees, with X-ray data processed with the latest XMM-LSS pipeline version. The present publication supersedes the Pierre et al.(2007) catalogue pertaining to the initial 5 square degrees. We provide X-ray source lists in the customary energy bands (0.5-2 and 2-10 keV) for a total of 6721 objects in the deep full-exposure catalogue and 5572 in the 10ks-limited one, above a detection likelihood of 15 in at least one band. We also provide a multiwavelength catalogue, cross-correlat…
Context. ULXs ($L_\textrm{X}>10^{39}$ erg s$^{-1}$) are excellent probes of accretion physics, star formation and IMBHs searches. As the sample size of X-ray data from modern observatories increases, producing extensive catalogues of ULXs and studying their collective properties is a possibility and a priority. Aims. We build a ULX catalogue based on one of the latest XMM-Newton releases, 4XMM-DR9, and the galaxy catalogue HECATE and study whether the properties of the expanded XMM-Newton ULX population are consistent with previous findings. Methods. We perform cross-matching between XMM-Newto…
Latent characterisation of the complete BATSE gamma ray bursts catalogue using Gaussian mixture of factor analysers and model-estimated overlap-based syncytial clustering
Michigan Technological University（密歇根理工大学）；Iowa State University（爱荷华州立大学）
We search for spectral features in Fermi-LAT gamma-rays coming from regions corresponding to eighteen brightest nearby galaxy clusters determined by the magnitude of their signal line-of-site integrals. We observe a double peak-like excess over the diffuse power-law background at photon energies 110 GeV and 130 GeV with the global statistical significance up to 3.6σ, confirming independently earlier claims of the same excess from Galactic centre. Interpreting this result as a signal of dark matter annihilations to two monochromatic photon channels in galaxy cluster haloes, and fixing the annih…
As part of the Chandra Galactic Bulge Survey (GBS), we present a catalogue of optical sources in the GBS footprint. This consists of two regions centered at Galactic latitude b = 1.5 degrees above and below the Galactic Centre, spanning (l x b) = (6x1) degrees. The catalogue consists of 2 or more epochs of observations for each line of sight in r', i' and Hα filters. It is complete down to r' = 20.2 and i' = 19.2 mag; the mean 5σ depth is r' = 22.5 and i' = 21.1 mag. The mean root-mean-square residuals of the astrometric solutions is 0.04 arcsec. We cross-correlate this optical catalogue with …
We compare the measured angular cross-correlation between the Fermi-LAT gamma-ray sky and catalogues of extra-galactic objects with the expected signal induced by weakly interacting massive particle (WIMP) dark matter (DM). We include a detailed description of the contribution of astrophysical gamma-ray emitters such as blazars, misaligned AGN and star forming galaxies, and perform a global fit to the measured cross-correlation. Five catalogues are considered: SDSS-DR6 quasars, 2MASS galaxies, NVSS radio galaxies, SDSS-DR8 Luminous Red Galaxies and SDSS-DR8 main galaxy sample. To model the cro…
