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151. CHAMP (Chandra Multiwavelength Project) Hard X-Ray Emitting AGN
ID:
ivo://nasa.heasarc/champhxagn
Title:
CHAMP (Chandra Multiwavelength Project) Hard X-Ray Emitting AGN
Short Name:
CHAMPHXAGN
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
This table contains the results from an X-ray and optical analysis of 188 active galactic nuclei (AGN) identified from 497 hard X-ray (observed flux in the (2.0 - 8.0 keV) band > 2.7 x 10<sup>-15</sup> erg/cm<sup>2</sup>/s) sources in 20 Chandra fields (1.5 square degrees) forming part of the Chandra Multiwavelength Project (ChaMP). These medium-depth X-ray observations enable the detection of a representative subset of those sources responsible for the bulk of the 2 - 8 keV cosmic X-ray background. Brighter than the survey's optical spectroscopic limit, the authors achieve a reasonable degree of completeness (77% of X-ray sources with counterparts r' < 22.5 have been classified): broad emission-line AGNs (62%), narrow emission-line galaxies (24%), absorption-line galaxies (7%), stars (5%), or clusters (2%). To construct a pure AGN sample, the authors required the rest-frame 2.0-8.0 keV luminosity (uncorrected for intrinsic absorption) to exceed 10<sup>42</sup> erg s<sup>-1</sup>, thereby excluding any sources that may contain a significant stellar or hot ISM component. The most luminous known star-forming or elliptical galaxies attain at most L<sub>X</sub> = 10<sup>42</sup> erg s<sup>-1</sup>. Since many of the traditional optical AGN signatures are not present in obscured sources, high X-ray luminosity becomes the authors' single discriminant for supermassive black hole accretion. They believe that almost all of the NELGs and ALGs harbor accreting SMBHs based on their X-ray luminosity. They find that 90% of the identified ChaMP sources have luminosities above this threshold. These selection criteria yield a sample of 188 AGNs from 20 Chandra fields with f(2-8 keV) > 2.7 x 10<sup>-15</sup> erg cm<sup>-2</sup> s<sup>-1</sup>, r' < 22.5, and L<sub>X</sub> > 10<sup>42</sup> erg s<sup>-1</sup>. The authors removed five objects identified as clusters based on their extended X-ray emission. This table was created by the HEASARC in March 2007 based on the CDS table J/ApJ/618/123, file table4.dat. This is a service provided by NASA HEASARC .
152. ChaMP Extended Stellar Survey (ChESS) X-Ray Catalog
ID:
ivo://nasa.heasarc/chesscat
Title:
ChaMP Extended Stellar Survey (ChESS) X-Ray Catalog
Short Name:
CHESSCAT
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The ChaMP Extended Stellar Survey (ChESS) X-ray catalog contains 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS). The authors used morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create this catalog, from a sample of 2121 matched ChaMP/SDSS sources. Their cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in their final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. New spectral classifications and H-alpha measurements are presented for an additional 79 stars. The catalog is dominated by main-sequence stars; the authors estimate the fraction of giants in ChESS to be ~10%. They identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. They derive distances from ~10 to 2000 pc for the stars in the catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities. These stars lie in a unique space in the L<sub>X</sub>-distance plane, filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys. For 36 newly identified X-ray-emitting M stars, the authors calculated L<sub>H-alpha</sub>/L<sub>bol</sub>. The quantities L<sub>H-alpha</sub>/L<sub>bol</sub> and L<sub>X</sub>/L<sub>bol</sub> are linearly related below L<sub>X</sub>/L<sub>bol</sub> ~ 3 x 10<sup>-4</sup>, while L<sub>H-alpha</sub>/L<sub>bol</sub> appears to turn over at larger L<sub>X</sub>/L<sub>bol</sub> values. Stars with reliable SDSS photometry have an ~0.1 mag blue excess in u-g, likely due to increased chromospheric continuum emission. Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy; the lowest activity sources belong to the old disk population, a clear signature of the decay of magnetic activity with age. This table was created by the HEASARC in January 2009 based on the electronic version of Tables 2 and 3 from the reference paper which were obtained from the ApJ web site. This is a service provided by NASA HEASARC .
153. ChaMPlane Galactic Bulge and Center X-Ray Source Catalog
ID:
ivo://nasa.heasarc/champlanex
Title:
ChaMPlane Galactic Bulge and Center X-Ray Source Catalog
Short Name:
CHAMPLANEX
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
This table contains the Chandra Multiwavelength Plane (ChaMPlane) Survey catalog of X-ray point sources in the window and four Galactic bulge fields, specifically all source detections with net counts >= 1 in the 0.3-8 keV broad band. In the reference paper, the authors present the log N-log S and spatial distributions of X-ray point sources in seven Galactic bulge (GB) fields within 4 degrees of the Galactic center (GC). They compare the properties of 1159 X-ray point sources discovered in their deep (100 ks) Chandra observations of three low extinction Window fields near the GC with the X-ray sources in the other GB fields centered around Sgr B2, Sgr C, the Arches Cluster, and Sgr A* using Chandra archival data. To reduce the systematic errors induced by the uncertain X-ray spectra of the sources coupled with field-and-distance-dependent extinction, they classify the X-ray sources using quantile analysis and estimate their fluxes accordingly. The result indicates that the GB X-ray population is highly concentrated at the center, more heavily than the stellar distribution models. It extends out to more than 1.4 degrees from the GC, and the projected density follows an empirical radial relation inversely proportional to the offset from the GC. They also compare the total X-ray and infrared surface brightness using the Chandra and Spitzer observations of the regions. The radial distribution of the total infrared surface brightness from the 3.6-micron band images appears to resemble the radial distribution of the X-ray point sources better than that predicted by the stellar distribution models. Assuming a simple power-law model for the X-ray spectra, the closer to the GC, the intrinsically harder the X-ray spectra appear, but adding an iron emission line at 6.7 keV in the model allows the spectra of the GB X-ray sources to be largely consistent across the region. This implies that the majority of these GB X-ray sources can be of the same or similar type. Their X-ray luminosity and spectral properties support the idea that the most likely candidate is magnetic cataclysmic variables (CVs), primarily intermediate polars (IPs). Their observed number density is also consistent with the majority being IPs, provided the relative CV to star density in the GB is not smaller than the value in the local solar neighborhood. This table was created by the HEASARC in January 2010, based on the electronic version of Table 2 from the reference paper, which was obtained from the Astrophysical Journal web site. This is a service provided by NASA HEASARC .
154. CHAMP/SDSS Nearby Low-Luminosity AGN Catalog
ID:
ivo://nasa.heasarc/champsdssa
Title:
CHAMP/SDSS Nearby Low-Luminosity AGN Catalog
Short Name:
CHAMPSDSSA
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The combination of the Sloan Digital Sky Survey (SDSS) and the Chandra Multiwavelength Project (ChaMP; Green et al. 2004, ApJS, 150, 43) currently offers the largest and most homogeneously selected sample of nearby galaxies for investigating the relations between X-ray nuclear emission, nebular line emission, black hole masses, and the properties of the associated stellar populations. The authors provide X-ray spectral fits and valid uncertainties for all the galaxies with counts ranging from 2 to 1325 (mean 76, median 19). They present in their paper novel constraints that both X-ray luminosity L<sub>X</sub> and X-ray spectral energy distribution bring to the galaxy evolutionary sequence HII -> Seyfert/Transition Object -> LINER -> Passive suggested by optical data. In particular, the authors show that both L<sub>X</sub> and Gamma, the slope of the power law that best fits the 0.5 - 8 keV spectra, are consistent with a clear decline in the accretion power along the sequence, corresponding to a softening of their spectra. This implies that, at z ~ 0, or at low-luminosity active galactic nucleus (AGN) levels, there is an anticorrelation between Gamma and L/L<sub>Edd</sub>, opposite to the trend which is exhibited by high-z AGN (quasars). The turning point in the Gamma - L/L<sub>Edd</sub> LLAGN + quasars relation occurs near Gamma ~ 1.5 and L/L<sub>Edd</sub> ~ 0.01. Interestingly, this is identical to what stellar mass X-ray binaries exhibit, indicating that the authors have probably found the first empirical evidence for an intrinsic switch in the accretion mode, from advection-dominated flows to standard (disk/corona) accretion modes in supermassive black hole accretors, similar to what has been seen and proposed to happen in stellar mass black hole systems. The anticorrelation the authors find between Gamma and L/L<sub>Edd</sub> may instead indicate that stronger accretion correlates with greater absorption. Therefore, the trend for softer spectra toward more luminous, high-redshift, and strongly accreting (L/L<sub>Edd</sub> >~ 0.01) AGNs/quasars could simply be the result of strong selection biases reflected in the dearth of type 2 quasar detections. The cross-match of all ChaMP sky regions imaged by Chandra/ACIS with the SDSS DR4 spectroscopic footprint results in a parent sample of 15,955 galaxies on or near a chip and a subset of 199 sources that are X-ray detected. Among those, only 107 sources have an off-axis angle (OAA) Theta <0.2 degrees and avoid ccd=8 due to high serial readout noise; these 107 objects comprise the main sample that the authors employ for this study and that are listed in this table. The authors performed direct spectral fits to the X-ray counts distribution using the full instrument calibration, known redshift, and Galactic 21-cm column nH<sub>Gal</sub>. Source spectra were extracted from circular regions with radii corresponding to energy encircled fractions of ~90%, while the background region encompasses a 20 arcsec annulus, centered on the source, with separation 4 arcsecs, from the source region. Any nearby sources were excised, from both the source and the background regions. The spectral fitting was done via yaxx ('Yet Another X-ray eXtractor': Aldcroft 2006, BAAS, 38, 376), an automated script that employs the CIAO Sherpa tool. Each spectrum was fitted in the range 0.5 - 8 keV by two different models: (1) a single power law plus absorption fixed at the Galactic 21-cm value (model 'PL'), and (2) a fixed power law of photon index Gamma = 1.9 plus intrinsic absorption of column nH (model 'PLfix'). For the nine objects with more than 200 counts, the authors employed a third model in which both the slope of the power law and the intrinsic absorption were free to vary (model 'PL_abs'). This table was created by the HEASARC in January 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/705/1336/">CDS Catalog J/ApJ/705/1336/</a> file table1.dat. This is a service provided by NASA HEASARC .
155. Chandra ACIS GSG Point-Like X-Ray Source Catalog
ID:
ivo://nasa.heasarc/cxogsgsrc
Title:
Chandra ACIS GSG Point-Like X-Ray Source Catalog
Short Name:
CXOGSGSRC
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The Chandra archival data are a valuable resource for various studies on different X-ray astronomy topics. In this paper, the authors utilize this wealth of information and present a uniformly processed data set, which can be used to address a wide range of scientific questions. The data analysis procedures are applied to 10,029 Advanced CCD Imaging Spectrometer observations, which produces 363,530 source detections belonging to 217,828 distinct X-ray sources. This number is twice the size of the Chandra Source Catalog (Version 1.1). The catalogs in this paper provide abundant estimates of the detected X-ray source properties, including source positions, counts, colors, fluxes, luminosities, variability statistics, etc. Cross-correlation of these objects with galaxies shows that 17,828 sources are located within the D<sub>25</sub> isophotes of 1,110 galaxies, and 7,504 sources are located between the D<sub>25</sub> and 2*D<sub>25</sub> isophotes of 910 galaxies. Contamination analysis with the log N-log S relation indicates that 51.3% of objects within 2*D<sub>25</sub> isophotes are truly relevant to galaxies, and the "net" source fraction increases to 58.9%, 67.3%, and 69.1% for sources with luminosities above 10<sup>37</sup>, 10<sup>38</sup>, and 10<sup>39</sup> erg/s, respectively. Among the possible scientific uses of this catalog mentioned in this paper, the authors discuss the possibility of studying intra-observation variability, inter-observation variability, and supersoft sources (SSSs). About 17,092 detected sources above 10 counts are classified as variable in individual observation with the Kolmogorov-Smirnov (K-S) criterion (P<sub>K-S</sub> < 0.01). There are 99,647 sources observed more than once and 11,843 sources observed 10 times or more, offering a wealth of data with which to explore their long-term variability. There are 1,638 individual objects (~2,350 detections) classified as SSSs. As a quite interesting subclass, detailed studies on X-ray spectra and optical spectroscopic follow-up are needed to categorize these SSSs and pinpoint their properties. In addition, this survey can enable a wide range of statistical studies, such as X-ray activity in different types of stars, X-ray luminosity functions in different types of galaxies, and multi-wavelength identification and classification of different X-ray populations. The ACIS observations were downloaded from the Chandra Data Archive on 2014 December 4, yielding 10,047 ACIS observations. Eighteen observations with PI as "Calibration" or Exposure as zero were excluded. Finally, there are 10,029 ACIS observations containing 4,146 ACIS-I observations and 5,883 ACIS-S observations in our sample. The exposure times for the selected observations cover a range from 50 s to 190 ks, with a total of 221,851 ks. This HEASARC table comprises the list of 218,789 X-ray point sources detected in the Chandra ACIS Survey and listed in the machine-readable version of Table 5 from the reference paper. This number is somewhat larger than the number of independent sources (217,828) stated in the abstract and Section 5 of the reference paper because if a source lies within 2*R<sub>25</sub> of more than one galaxy it is listed multiple times, once for each galaxy with which it may be associated. All parameters are the same for such duplicate cases except for the entry_number, alt_name, adopted_distance, luminosity, src_nucleus_offset, norm_src_nucleus_offset and (in some cases) source_type. This table was created by the HEASARC in March 2017 primarily based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/224/40/">CDS Catalog J/ApJS/224/40/</a> file table5.dat, the catalog of X-ray point sources in the Chandra ACIS Survey. The positional information for these sources was taken from <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/224/40/">CDS Catalog J/ApJS/224/40/</a> file table3.dat, the list of separation detections for these X-ray sources, using the first listed detection in each case. This is a service provided by NASA HEASARC .
156. Chandra ACIS Survey for X-Ray AGN in Nearby Galaxies
ID:
ivo://nasa.heasarc/chansngcat
Title:
Chandra ACIS Survey for X-Ray AGN in Nearby Galaxies
Short Name:
CHANSNGCAT
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The authors searched the public archive of the Chandra X-ray Observatory as of 2016 March and assembled a sample of 719 galaxies within 50 Mpc with available Advanced CCD Imaging Spectrometer observations. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H II nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 10<sup>37</sup> erg/s on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results were to be reported in forthcoming papers, e.g., She et al. (2017, ApJ, 842, 131). The sample was assembled based on Chandra/ACIS observations that were publicly available as of 2016 March. The authors first generated a full list of ACIS observations, and then searched in the NASA/IPAC Extragalactic Database (NED) for galaxies within 50 Mpc whose nuclear positions were less than 8 arcminutes from the aim point of any Chandra observation. The adopted distances were taken from NED, in the following order of priority: surface brightness fluctuations, Cepheid variables, tip of the red giant branch, Type Ia supernovae, the fundamental plane, Faber-Jackson relation, Tully-Fisher relation. If more than one reference is available for the distance by the same means, the latest one is selected, unless otherwise specified. Whenever possible, the authors obtain positions of the galaxy nuclei based on measurements from near-infrared images, which suffer from less obscuration by dust or confusion from young star-forming regions. Most of the data come from the Two-Micron All Sky Survey (2MASS) extended source catalog (Skrutskie et al. 2006, AJ, 131, 1163), or NED otherwise. In a few cases, the NED positions come from radio observations. The authors discarded galaxies whose nuclear positions in NED were obtained from X-ray observations. This table was created by the HEASARC in September 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/835/223">CDS Catalog J/ApJ/835/223</a> files table1.dat, table2.dat and table4.dat. This is a service provided by NASA HEASARC .
157. Chandra ACIS Survey of Nearby Galaxies X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/chngpscliu
Title:
Chandra ACIS Survey of Nearby Galaxies X-Ray Point Source Catalog
Short Name:
CHNGPSCLIU
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The Chandra data archive is a treasure trove for various studies, and in this study the author exploits this valuable resource to study the X-ray point source populations in nearby galaxies. By 2007 December 14, 383 galaxies within 40 Mpc with isophotal major axes above 1 arcminute had been observed by 626 public ACIS observations, most of which were for the first time analyzed by this survey to study the X-ray point sources. Uniform data analysis procedures were applied to the 626 ACIS observations and led to the detection of 28,099 point sources, which belong to 17,559 independent sources. These include 8700 sources observed twice or more and 1000 sources observed 10 times or more, providing a wealth of data to study the long-term variability of these X-ray sources. Cross-correlation of these sources with galaxy isophotes led to 8,519 sources within the D<sub>25</sub> isophotes of 351 galaxies, 3,305 sources between the D<sub>25</sub> and 2 * D<sub>25</sub> isophotes of 309 galaxies, and an additional 5,735 sources outside the 2 * D<sub>25</sub> isophotes of galaxies. This survey has produced a uniform catalog, by far the largest, of 11,824 X-ray point sources within 2 * D<sub>25</sub> isophotes of 380 galaxies. Contamination analysis using the log N-log S relation shows that 74% of the sources within the 2 * D<sub>25</sub> isophotes above 10<sup>39</sup> erg s<sup>-1</sup>, 71% of the sources above 10<sup>38</sup> erg s<sup>-1</sup>, 63% of the sources above 10<sup>37</sup> erg s<sup>-1</sup>, and 56% of all sources are truly associated with the galaxies. Meticulous efforts have identified 234 X-ray sources with galactic nuclei of nearby galaxies. This archival survey leads to 300 ultraluminous X-ray sources (ULXs) with L<sub>X</sub> in the 0.3-8 keV band >= 2 x 10<sup>39</sup> erg s<sup>-1</sup> within the D<sub>25</sub> isophotes, 179 ULXs between the D<sub>25</sub> and the 2 * D<sub>25</sub> isophotes, and a total of 479 ULXs within 188 host galaxies, with about 324 ULXs truly associated with the host galaxies based on the contamination analysis. About 4% of the sources exhibited at least one supersoft phase, and 70 sources are classified as ultraluminous supersoft sources with L<sub>X</sub> (0.3-8 keV) >= 2 x 10<sup>38</sup> erg s<sup>-1</sup>. With a uniform data set and good statistics, this survey enables future works on various topics, such as X-ray luminosity functions for the ordinary X-ray binary populations in different types of galaxies, and X-ray properties of galactic nuclei. This table contains the list of 17,559 'independent' X-ray point sources that was contained in table 4 of the reference paper. As the author notes in Section 5 of this paper, there are 341 sources projected within 2 galaxies with overlapping domains which are listed for both galaxies. The 5,735 sources lieing outside the 2* D<sub>25</sub> isophotes of the galaxies are also included in this table. For these sources, the X-ray luminosities are computed as if they were in a galaxy of that group, which may or may not be the case; thus, they may not be their 'true' luminosities, but are listed for the purposes of comparison. This table was created by the HEASARC in March 2011 based on the electronic version of Table 4 of the reference paper which was obtained from the Astrophysical Journal web site. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018. This is a service provided by NASA HEASARC .
158. Chandra Archive Of Galaxies Ultraluminous X-Ray Source Catalog
ID:
ivo://nasa.heasarc/chanulxcat
Title:
Chandra Archive Of Galaxies Ultraluminous X-Ray Source Catalog
Short Name:
CHANULXCAT
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
One hundred fifty-five (the abstract in the paper erroneously states the number to be 154) discrete, non-nuclear, ultraluminous X-ray (ULX) sources, with spectroscopically determined intrinsic X-ray luminosities greater than 10<sup>39</sup> erg/s, have been identified in 82 galaxies that were observed with Chandra's Advanced CCD Imaging Spectrometer (ACIS). Positions, X-ray luminosities, and spectral and timing characteristics of these ULXs are contained in this table. Eighty-three percent of ULX candidates have spectra that can be described as absorbed power laws with mean index Gamma = 1.74 and column density N<sub>H</sub> = 2.24 x 10<sup>21</sup> atoms cm<sup>-2</sup>, or ~5 times the average Galactic column. About 20% of the ULXs have much steeper indices indicative of a soft, and likely thermal, spectrum. The locations of ULXs in their host galaxies are strongly peaked toward their galaxy centers. The deprojected radial distribution of the ULX candidates is somewhat steeper than an exponential disk, indistinguishable from that of the weaker sources. About 5%-15% of ULX candidates are variable during the Chandra observations (which average 39.5 ks). Comparison of the cumulative X-ray luminosity functions of the ULXs to Chandra Deep Field results suggests ~25% of the sources may be background objects, including 14% of the ULX candidates in the sample of spiral galaxies and 44% of those in elliptical galaxies, implying the elliptical galaxy ULX population is severely compromised by background active galactic nuclei. Correlations with host galaxy properties confirm the number and total X-ray luminosity of the ULXs are associated with recent star formation and with galaxy merging and interactions. The preponderance of ULXs in star-forming galaxies as well as their similarities to less-luminous sources suggest they originate in a young but short-lived population such as the high-mass X-ray binaries, with a smaller contribution (based on spectral slope) from recent supernovae. The number of ULXs in elliptical galaxies scales with host galaxy mass and can be explained most simply as the high-luminosity end of the low-mass X-ray binary population. This table was created by the HEASARC in March 2007 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/154/519">CDS catalog J/ApJS/154/519</a> file table2.dat. This is a service provided by NASA HEASARC .
159. Chandra Bulge Field X-Ray Point Source Catalog
ID:
ivo://nasa.heasarc/cbfgrxecxo
Title:
Chandra Bulge Field X-Ray Point Source Catalog
Short Name:
CBFGRXECXO
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
Apparently diffuse X-ray emission has been known to exist along the central quarter of the Galactic Plane since the beginning of X-ray astronomy; this is referred to as the Galactic Ridge X-ray emission (GRXE). Recent deep X-ray observations have shown that numerous X-ray point sources account for a large fraction of the GRXE in the hard band (2 - 8 keV). However, the nature of these sources is poorly understood. Using the deepest X-ray observations made in the Chandra bulge field, the authors present the result of a coherent photometric and spectroscopic analysis of individual X-ray point sources for the purpose of constraining their nature and deriving their fractional contributions to the hard-band continuum and Fe K line emission of the GRXE. Based on the X-ray color-color diagram, they divided the point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). The group A sources are further decomposed spectrally into thermal and non-thermal sources with different fractions in different flux ranges. From their X-ray properties, the authors speculate that the group A non-thermal sources are mostly active galactic nuclei and the thermal sources are mostly white dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and C sources are X-ray active stars in flares and quiescence, respectively. In the log N - log S curve of the 2 - 8 keV band, the group A non-thermal sources are dominant above ~10<sup>-14</sup> erg/cm<sup>2</sup>/s, which is gradually taken over by Galactic sources in the fainter flux ranges. The Fe K-alpha emission is mostly from the group A thermal (WD binaries) and the group B (X-ray active stars) sources. The authors retrieved 10 archived data sets of the Chandra bulge field (CBF) taken with the Advanced CCD Imaging Spectrometer-I (ACIS-I; 0.5 - 8.0 keV energy band with a spectral resolution of ~280 eV for the full width at half-maximum at 5.9keV) array on board Chandra. The observations were carried out from 2008 May to August with a total exposure time of ~900 ks. The authors first extracted point-source candidates using the wavdetect algorithm in the CIAO package. They set the significance threshold at 2.5 x 10<sup>-5</sup>, implying that one false positive detection would be expected at every 4 x 10<sup>4</sup> trials. As a result, 2596 source candidates were found. The number of their source candidates is nearly the same as that found by Revnivtsev et al.(2009, A&A, 507, 1211) in the same region. To select significant point sources from the candidates, the authors examined their validity based on their photometric significance (PS) and the probability of no source (P<sub>B</sub>). The PS is defined as the background-subtracted source counts (C<sub>net</sub>) divided by its background counts normalized by the area. P<sub>B</sub> is the probability that the source is attributable to a background fluctuation, assuming Poisson statistics. The authors recognized a source to be valid if it satisfied both these criteria: PS >= 1.0 and P<sub>B</sub> <= 1.0 x 10<sup>-2</sup>. As a result, they obtained 2002 valid point sources. This table was created by the HEASARC in December 2014 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/766/14">CDS catalog J/ApJ/766/14</a> file table2.dat. This is a service provided by NASA HEASARC .
160. Chandra COSMOS (C-COSMOS) Survey Optical/IR Counterparts Catalog
ID:
ivo://nasa.heasarc/ccosmosoid
Title:
Chandra COSMOS (C-COSMOS) Survey Optical/IR Counterparts Catalog
Short Name:
CCOSMOSOID
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8-Ms, Chandra program that has imaged the central 0.9 deg<sup>2</sup> of the COSMOS field down to limiting depths of 1.9 x 10<sup>-16</sup> erg/cm<sup>2</sup>/s in the soft (0.5-2 keV) band, 7.3 x 10<sup>-16</sup> erg/cm<sup>2</sup>/s in the hard (2-10 keV) band, and 5.7 x 10<sup>-16</sup> erg/cm<sup>2</sup>/s in the full (0.5-10 keV) band. In this Paper III of the series of papers on this survey, the authors report the i, K, and 3.6-um identifications of the 1761 X-ray point sources. They use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources, they were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only two sources are truly empty fields. The full catalog, including spectroscopic and photometric redshifts and classification described here in detail, is available herein. See also the related table <a href="ccosmoscat.html">CCOSMOSCAT</a> for the the surveyed X-ray point sources. This table was created by the HEASARC in December 2012, based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/201/30">CDS Catalog J/ApJS/201/30</a> file catalog.dat. This is a service provided by NASA HEASARC .