- ID:
- ivo://CDS.VizieR/J/AJ/161/154
- Title:
- 3FGL X-ray Analysis and ML
- Short Name:
- J/AJ/161/154
- Date:
- 07 Mar 2022 07:09:03
- Publisher:
- CDS
- Description:
- We conduct X-ray spectral fits on 184 likely counterparts to Fermi-LAT 3FGL unassociated sources. Characterization and classification of these sources allows for more complete population studies of the high-energy sky. Most of these X-ray spectra are well fit by an absorbed power law model, as expected for a population dominated by blazars and pulsars. A small subset of 7 X-ray sources have spectra unlike the power law expected from a blazar or pulsar and may be linked to coincident stars or background emission. We develop a multiwavelength machine learning classifier to categorize unassociated sources into pulsars and blazars using gamma- and X-ray observations. Training a random forest procedure with known pulsars and blazars, we achieve a cross-validated classification accuracy of 98.6%. Applying the random forest routine to the unassociated sources returned 126 likely blazar candidates (defined as P_bzr_>90%) and 5 likely pulsar candidates (P_bzr_<10%). Our new X-ray spectral analysis does not drastically alter the random forest classifications of these sources compared to previous works, but it builds a more robust classification scheme and highlights the importance of X-ray spectral fitting. Our procedure can be further expanded with UV, visual, or radio spectral parameters or by measuring flux variability.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/811/58
- Title:
- FIR properties of SDSS 0.1<z<5 quasars
- Short Name:
- J/ApJ/811/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the public data from the Herschel wide-field surveys, we study the far-infrared properties of optical-selected quasars from the Sloan Digital Sky Survey. Within the common area of ~172deg^2^, we have identified the far-infrared counterparts for 354 quasars, among which 134 are highly secure detections in the Herschel 250um band (signal-to-noise ratios >=5). This sample is the largest far-infrared quasar sample of its kind, and spans a wide redshift range of 0.14<=z<=4.7. Their far-infrared spectral energy distributions, which are due to the cold-dust components within the host galaxies, are consistent with being heated by active star formation. In most cases (>~80%), their total infrared luminosities as inferred from only their far-infrared emissions (L_IR_^(cd)^) already exceed 10^12^L_{sun}_, and thus these objects qualify as ultra-luminous infrared galaxies. There is no correlation between L_IR_^(cd)^ and the absolute magnitudes, the black hole masses or the X-ray luminosities of the quasars, which further support that their far-infrared emissions are not due to their active galactic nuclei. A large fraction of these objects (>~50%-60%) have star-formation rates >~300M_{sun}_/yr. Such extreme starbursts among optical quasars, however, is only a few percent. This fraction varies with redshift, and peaks at around z~2. Among the entire sample, 136 objects have secure estimates of their cold-dust temperatures (T), and we find that there is a dramatic increasing trend of T with increasing L_IR_^(cd)^. We interpret this trend as the envelope of the general distribution of infrared galaxies on the (T, L_IR_^(cd)^) plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/704/1570
- Title:
- Fitting LINERs within the AGN family
- Short Name:
- J/ApJ/704/1570
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we study the nuclear obscuration of galaxies hosting low ionization narrow emission regions (LINERs) based on their X-ray and optical emission. They show column densities at soft energies (0.5-2keV) mostly related to the diffuse emission around the active galactic nucleus (AGN), showing a correlation with the optical extinction. Column densities at hard energies (2-10keV) seem to be much higher than what would be expected from the optical extinction. They might be associated with the inner regions of the AGN, buried at optical wavelengths.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A141
- Title:
- Flux-limited sample of HBL blazars, OUSXG
- Short Name:
- J/A+A/642/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analysed all the X-ray images centred on Gamma Ray Bursts generated by Swift over the last 15 years using automatic tools that do not require any expertise in X-ray astronomy, producing results in excellent agreement with previous findings. This work, besides presenting the largest medium-deep survey of the X-ray sky and a complete sample of blazars, wishes to be a step in the direction of achieving the ultimate goal of the Open Universe Initiative, that is to enable non expert people to fully benet of space science data, possibly extending the potential for scientific discovery, currently conned within a small number of highly specialised teams, to a much larger population. We have used the Swift deepsky Docker container encapsulated pipeline to build the largest existing flux-limited and unbiased sample of serendipitous X-ray sources. Swift deepsky runs on any laptop or desktop computer with a modern operating system. The tool automatically downloads the data and the calibration files from the archives, runs the official Swift analysis software and produces a number of results including images, the list of detected sources, X-ray fluxes, SED data, and spectral slope estimations. We used our source list to build the LogN-LogS of extra-galactic sources, which perfectly matches that estimated by other satellites. Combining our survey with multi-frequency data we selected a complete radio flux-density limited sample of High Energy Peaked (HBL) blazars. The LogN-LogS built with this data-set confirms that previous samples are incomplete below ~20mJy.
365. Fossil galaxy groups
- ID:
- ivo://CDS.VizieR/J/AJ/137/3942
- Title:
- Fossil galaxy groups
- Short Name:
- J/AJ/137/3942
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use SDSS-DR4 photometric and spectroscopic data out to redshift z~0.1 combined with ROSAT All Sky Survey X-ray data to produce a sample of 25 fossil groups (FGs), defined as bound systems dominated by a single, luminous elliptical galaxy with extended X-ray emission. We examine possible biases introduced by varying the parameters used to define the sample, and the main pitfalls are also discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/2735
- Title:
- Four close dSph XXM observations
- Short Name:
- J/MNRAS/451/2735
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the analysis of deep archival XMM-Newton observations towards the dwarf spheroidal galaxies Draco, Leo I, Ursa Major II (UMa II) and Ursa Minor (UMi) in the Milky Way neighbourhood. The X-ray source population is characterized and cross-correlated with available databases to infer their nature. We also investigate if intermediate-mass black holes are hosted in the centre of these galaxies. For Draco, we detect 96 high-energy sources, two of them possibly being local stars, while no evidence for any X-ray emitting central compact object is found. Towards the Leo I and UMa II fields of view, we reveal 116 and 49 X-ray sources, respectively. None of them correlates with the putative central black holes and only one is likely associated with a UMa II local source. The study of the UMi dwarf galaxy found 54 high-energy sources and a possible association with a source at the dwarf spheroidal galaxy centre. We put an upper limit on the luminosity of the central compact object of 4.02x10^33^erg/s. Furthermore, via the correlation with a radio source near the galactic centre, the putative black hole should have a mass of (2.76^+32.00^_-2.54_)x10^6^M_{sun}_ and be radiatively inefficient. This confirms a previous result obtained using Chandra data alone.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/105
- Title:
- Fourth catalog of Fermi LAT-detected AGNs (4LAC)
- Short Name:
- J/ApJ/892/105
- Date:
- 17 Jan 2022 00:31:09
- Publisher:
- CDS
- Description:
- The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains 2863 objects located at high Galactic latitudes (|b|>10{deg}). It includes 85% more sources than the previous 3LAC catalog based on 4yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50MeV to 1TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.
- ID:
- ivo://CDS.VizieR/IX/4
- Title:
- Fourth UHURU Catalogue (4U)
- Short Name:
- IX/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fourth Uhuru (4U) Catalog lists 339 X-ray sources that were observed with the Uhuru (SAS A) X-ray observatory. It contains positional information in the form of 90% confidence level error boxes, 2-6keV intensities, possible optical and radio counterparts, and alternative names for sources observed in earlier compilations. The major classes of identified objects include binary stellar systems, supernova remnants, Seyfert galaxies, clusters of galaxies, and possibly the new class of superclusters of galaxies. The Uhuru satellite was a scanning X-ray instrument with a narrow (1 by 10 degree FWFM) and a wide (10 by 10 degree FWFM) collimator (cf. Giacconi et al. 1971ApJ...165L..27G). Typically, the scan rate was 0.5degree/second, with the spin axis in one position for roughly one day. During the interval for which the spin axis was fixed, repeated scans were made of the same 10 by 360 degrees band of the sky. For this catalog, the individual scans were superposed using aspect data from an orthogonally mounted triad of magnetometers and a Sun sensor onboard the spacecraft, supplemented by observations of well-located X-ray sources. The observations employed in producing this catalog were obtained over a total of 429 days between 1970 December 12 and 1973 March 18, apart from a gap between 1972 July and December when the spacecraft's transmitter was operating improperly.
- ID:
- ivo://CDS.VizieR/J/MNRAS/438/2839
- Title:
- Galactic Bulge Survey X-ray sources NIR ctp
- Short Name:
- J/MNRAS/438/2839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the near-infrared matches, drawn from three surveys, to the 1640 unique X-ray sources detected by Chandra in the Galactic Bulge Survey (GBS). This survey targets faint X-ray sources in the bulge, with a particular focus on accreting compact objects. We present all viable counterpart candidates and associate a false alarm probability (FAP) to each near-infrared match in order to identify the most likely counterparts. The FAP takes into account a statistical study involving a chance alignment test, as well as considering the positional accuracy of the individual X-ray sources. We find that although the star density in the bulge is very high, ~90 per cent of our sources have an FAP<10 per cent, indicating that for most X-ray sources, viable near-infrared counterparts candidates can be identified. In addition to the FAP, we provide positional and photometric information for candidate counterparts to ~95 per cent of the GBS X-ray sources. This information in combination with optical photometry, spectroscopy and variability constraints will be crucial to characterize and classify secure counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJS/181/110
- Title:
- Galactic center X-ray sources
- Short Name:
- J/ApJS/181/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2{deg}x0.8{deg} field around the Galactic center. This enlarges the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25Ms of exposure. At the distance to the Galactic center (8kpc), we are sensitive to sources with luminosities of 4x10^32^erg/s (0.5-8.0keV; 90% confidence) over an area of 1deg^2^, and up to an order of magnitude more sensitive in the deepest exposure (1.0Ms) around Sgr A*. The positions of 60% of our sources are accurate to <1" (95% confidence), and 20% have positions accurate to <0.5". We search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7-285218, with a periodic 1745s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8{sigma} evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l~0.1{deg}.
