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CXOGSGSRC - Chandra ACIS GSG Point-Like X-Ray Source Catalog



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 D25 isophotes of 1,110 galaxies, and 7,504 sources are located between the D25 and 2*D25 isophotes of 910 galaxies. Contamination analysis with the log N-log S relation indicates that 51.3% of objects within 2*D25 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 1037, 1038, and 1039 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 (PK-S < 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*R25 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.

Catalog Bibcode



CHANDRA ACIS survey of X-ray point sources: the source catalog.
    Wang S., Liu J., Qiu Y., Bai Y., Yang H., Guo J., Zhang P.
   <Astrophys. J. Suppl. Ser., 224, 40-40 (2016)>
   =2016ApJS..224...40W    (SIMBAD/NED BibCode)


This table was created by the HEASARC in March 2017 primarily based on CDS Catalog J/ApJS/224/40/ file table5.dat, the catalog of X-ray point sources in the Chandra ACIS Survey. The positional information for these sources was taken from CDS Catalog J/ApJS/224/40/ file table3.dat, the list of separation detections for these X-ray sources, using the first listed detection in each case.

Sources with Negative Distances in Original Table

There were 49 sources in the original table which had negative adopted distances of -0.20 Mpc, the significance of which is unclear. The HEASARC has reset these distances to 0.20 Mpc in all cases. The sources in question are listed below:
|name                   |alt_name    |ra         |dec        |error_radius|src_nucleus_offset|distance|lx       |flux    |max_significance|
|CXOGSG J024055.0+593130|            |02 40 55.05|+59 31 30.0|        4.14|                  | -0.2000|2.890e+35|6.02e-14|           4.972|
|CXOGSG J024056.8+593303|            |02 40 56.90|+59 33 03.3|        2.38|                  | -0.2000|5.230e+35|1.09e-13|           9.890|
|CXOGSG J024107.3+593327|            |02 41 07.30|+59 33 27.3|        3.25|                  | -0.2000|1.220e+35|2.55e-14|           3.083|
|CXOGSG J024110.0+593515|            |02 41 09.99|+59 35 15.5|        1.37|                  | -0.2000|4.150e+35|6.57e-14|          11.051|
|CXOGSG J024117.5+593319|            |02 41 17.52|+59 33 19.4|        3.16|                  | -0.2000|6.860e+34|1.43e-14|           2.565|
|CXOGSG J024120.1+593314|            |02 41 20.16|+59 33 14.7|        2.82|                  | -0.2000|8.350e+34|1.74e-14|           2.845|
|CXOGSG J024122.3+592917|            |02 41 22.37|+59 29 17.8|        3.61|                  | -0.2000|2.440e+35|4.36e-14|           4.800|
|CXOGSG J024125.0+593451|            |02 41 25.01|+59 34 51.1|        1.61|                  | -0.2000|1.230e+35|2.57e-14|           4.472|
|CXOGSG J024126.7+593454|            |02 41 26.73|+59 34 54.0|        1.11|                  | -0.2000|2.450e+35|3.98e-14|           7.620|
|CXOGSG J024131.0+593630|            |02 41 31.05|+59 36 30.5|        1.00|                  | -0.2000|3.900e+36|7.90e-13|         113.898|
|CXOGSG J024131.3+593339|            |02 41 31.36|+59 33 39.3|        1.86|                  | -0.2000|8.500e+34|1.77e-14|           3.433|
|CXOGSG J024138.3+593008|            |02 41 38.39|+59 30 08.6|        4.66|                  | -0.2000|5.140e+34|1.07e-14|           1.847|
|CXOGSG J024139.3+593715|            |02 41 39.31|+59 37 15.2|        1.00|                  | -0.2000|1.300e+36|2.45e-13|          46.069|
|CXOGSG J024142.0+593511|            |02 41 41.99|+59 35 11.2|        1.00|                  | -0.2000|3.010e+35|5.81e-14|          12.574|
|CXOGSG J024142.1+593527|            |02 41 42.13|+59 35 27.8|        1.00|                  | -0.2000|2.250e+35|4.44e-14|           9.648|
|CXOGSG J024144.8+593734|            |02 41 44.88|+59 37 34.8|        1.00|                  | -0.2000|9.650e+35|1.52e-13|          28.522|
|CXOGSG J024145.9+593457|            |02 41 45.95|+59 34 57.1|        1.00|                  | -0.2000|3.820e+35|7.96e-14|          15.674|
|CXOGSG J024148.0+593003|            |02 41 47.95|+59 30 03.7|        3.25|                  | -0.2000|9.360e+34|1.66e-14|           3.194|
|CXOGSG J024149.2+593343|            |02 41 49.28|+59 33 44.0|        1.10|                  | -0.2000|1.060e+35|2.20e-14|           4.776|
|CXOGSG J024149.3+593511|            |02 41 49.36|+59 35 11.3|        1.00|                  | -0.2000|1.800e+35|2.78e-14|           8.133|
|CXOGSG J024151.8+593608|PGC 10217 X3|02 41 51.90|+59 36 08.4|        1.00|             0.346| -0.2000|6.290e+34|1.10e-14|           2.975|
|CXOGSG J024154.1+593735|            |02 41 54.15|+59 37 35.5|        1.00|                  | -0.2000|1.500e+35|3.13e-14|           4.032|
|CXOGSG J024154.7+593749|            |02 41 54.74|+59 37 49.9|        1.02|                  | -0.2000|5.950e+34|1.24e-14|           2.482|
|CXOGSG J024154.7+593406|            |02 41 54.78|+59 34 06.6|        1.00|                  | -0.2000|2.870e+35|5.52e-14|          12.592|
|CXOGSG J024154.9+593615|PGC 10217 X2|02 41 55.03|+59 36 15.3|        1.00|             0.090| -0.2000|1.680e+35|3.50e-14|           6.506|
|CXOGSG J024157.7+593714|            |02 41 57.72|+59 37 14.4|        1.00|                  | -0.2000|7.340e+34|1.53e-14|           2.530|
|CXOGSG J024158.1+593708|            |02 41 58.10|+59 37 08.9|        1.00|                  | -0.2000|1.330e+35|2.77e-14|           4.542|
|CXOGSG J024200.4+593526|            |02 42 00.45|+59 35 26.4|        1.00|                  | -0.2000|1.250e+35|2.07e-14|           2.526|
|CXOGSG J024201.3+593606|PGC 10217 X1|02 42 01.34|+59 36 06.5|        1.00|             0.855| -0.2000|2.560e+35|5.33e-14|           2.028|
|CXOGSG J024202.0+593646|            |02 42 02.01|+59 36 47.0|        1.00|                  | -0.2000|2.100e+35|4.38e-14|           2.110|
|CXOGSG J024202.2+593843|            |02 42 02.22|+59 38 43.1|        1.00|                  | -0.2000|7.730e+35|1.45e-13|          23.011|
|CXOGSG J024203.0+593300|            |02 42 03.03|+59 33 00.9|        1.00|                  | -0.2000|3.050e+35|4.36e-14|          10.616|
|CXOGSG J024206.2+593341|            |02 42 06.18|+59 33 41.3|        1.44|                  | -0.2000|7.820e+34|1.42e-14|           3.004|
|CXOGSG J024208.4+593642|            |02 42 08.47|+59 36 42.6|        1.10|                  | -0.2000|7.150e+34|1.49e-14|           2.498|
|CXOGSG J024209.4+593607|            |02 42 09.46|+59 36 07.9|        1.15|                  | -0.2000|5.470e+34|1.14e-14|           2.519|
|CXOGSG J024211.3+593419|            |02 42 11.35|+59 34 20.0|        1.00|                  | -0.2000|1.650e+35|2.86e-14|           7.417|
|CXOGSG J024211.7+593149|            |02 42 11.75|+59 31 49.4|        1.34|                  | -0.2000|2.850e+35|4.65e-14|           7.841|
|CXOGSG J024211.8+593114|            |02 42 11.90|+59 31 14.8|        2.77|                  | -0.2000|9.500e+34|1.98e-14|           2.743|
|CXOGSG J024216.2+593857|            |02 42 16.26|+59 38 57.8|        1.54|                  | -0.2000|1.050e+35|2.19e-14|           3.098|
|CXOGSG J024225.9+594432|            |02 42 26.00|+59 44 32.7|        4.50|                  | -0.2000|2.770e+35|5.77e-14|           4.083|
|CXOGSG J024227.9+593058|            |02 42 27.99|+59 30 58.6|        2.07|                  | -0.2000|3.130e+35|4.97e-14|           6.067|
|CXOGSG J024231.3+593245|            |02 42 31.40|+59 32 45.9|        3.07|                  | -0.2000|8.020e+34|1.67e-14|           2.659|
|CXOGSG J024235.0+593508|            |02 42 34.98|+59 35 08.6|        1.71|                  | -0.2000|1.540e+35|2.57e-14|           5.388|
|CXOGSG J024238.0+593600|            |02 42 38.08|+59 36 00.4|        1.96|                  | -0.2000|1.430e+35|2.98e-14|           4.665|
|CXOGSG J024241.7+594043|            |02 42 41.90|+59 40 43.6|        2.67|                  | -0.2000|2.450e+35|5.02e-14|           4.768|
|CXOGSG J024243.9+593036|            |02 42 43.97|+59 30 36.5|        5.31|                  | -0.2000|1.160e+35|2.42e-14|           2.950|
|CXOGSG J024253.1+594056|            |02 42 53.17|+59 40 56.6|        4.17|                  | -0.2000|1.760e+35|3.66e-14|           4.240|
|CXOGSG J024300.8+593339|            |02 43 00.88|+59 33 39.4|        4.43|                  | -0.2000|1.830e+35|3.81e-14|           3.849|
|CXOGSG J024304.1+593520|            |02 43 04.12|+59 35 20.2|        4.40|                  | -0.2000|2.010e+35|4.19e-14|           3.832|


This parameter contains a HEASARC-created unique sequential identification number for each entry in the catalog.

The group number to which the X-ray source belongs. Each source record in the catalog was constructed by combining source detections from multiple observations, which required matching the source detections from all of the observations that included the same region of the sky. A first step was to divide the 10,029 ACIS observations into 4,683 groups based on the proximity of the pointings. The observations in the same group with overlapping fields of view were hence studied together. There are 1,145 groups with two or more Chandra ACIS observations, including seven groups (group 1, 2, 5, 7, 11, 13, and 28) with more than 100 observations.

The IAU-style J2000.0 position-based source designation for the the Chandra X-ray source, viz., 'CXOGSG JHHMMSS.s+DDMMSS', registered with the Dictionary of Nomenclature of Celestial Objects, where the 'GSG' part of the prefix indicates that the source was named by the Galaxy Structure Group of the National Astronomical Observatories, Chinese Academy of Sciences.

The galaxy source name given by the authors to the X-ray source, e.g., 'NGC 224 X610'. In each galaxy, the X-ray sources are numbered sequentially based on their maximum detection significance. The criterion for associating a source with a galaxy is that it lies within 2*R25 of the center of the galaxy, where the R25 is the elliptical radius of the D25 isophote along the great arc connecting the galaxy center and the source. Generally, a source is regarded as being associated with a galaxy if it is located within the D25 isophote, but here a source with separation s in the range R25 < s < 2*R25 is also considered to belong to the galaxy to avoid missing any galactic sources. All of the galaxy information (e.g., coordinates, R25, distance) come from the Third Reference Catalog of Galaxies (RC3). Cross-correlation of these sources with galaxy isophotes yields 17,828 sources within the D25 isophotes of 1,110 galaxies, and 7,504 sources between the D25 and 2*D25 isophotes of 910 galaxies. Note that the authors have made no attempt herein to exclude contaminating foreground stars or background QSOs or AGN. See Section 5 of the reference paper for their estimate of the expected contamination rate.

Sources marked with 'M' are projected within the 2*R25 domains of two or more galaxies that have overlapping domains. This implies that such a source will have multiple entries, one for each galaxy with which it is potentially associated (see Overview above for more details).

The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-5 degrees (0.036 arcseconds) in the original tables.

The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-5 degrees (0.036 arcseconds) in the original tables.

The Galactic Longitude of the X-ray source.

The Galactic Latitude of the X-ray source.

The statistical positional error of the X-ray source, in arcseconds, calculated using the scheme of Kim et al. (2007, ApJS, 169, 401). See Section 2.2 of the reference paper for more details.

For sources which are projected within 2*R25 of a galaxy, the angular offset of the source from the nucleus, in arcminutes.

For sources which are projected within 2*R25 of a galaxy, the angular offset of the source from the nucleus, in units of the galaxy's elliptical radius R25.

The distance adopted to the X-ray source, in Mpc. If the source is projected within 2*R25 of the nucleus of a galaxy, this is the distance to the galaxy in RC3. If the distance of the host galaxy is unknown, or if an X-ray source is not associated with a galaxy, then the distance for the source is assumed to be 1 Mpc. There were 49 sources in the original table which had negative adopted distances of -0.20 Mpc, the significance of which is unclear. The HEASARC has reset these distances to 0.20 Mpc in all such cases (see the list of these sources in the Sources_with_Negative_Distances_in_Original_Table section above.

The number of times that the source was observed/detected. Thus, '2/1' means that the source was observed twice and detected once.

The inferred X-ray luminosity LX of the source in the 0.3-8.0 keV energy range, in erg s-1, assuming the quoted adopted distance and X-ray flux. For sources with multiple detections, the maximum flux is used, and hence in such cases this will be the maximum luminosity.

The flux of the X-ray source FX in the 0.3-8.0 keV energy range, in erg s-1 cm-2, averaged over all of its detections. The source flux is calculated for each source from its count rate, which is computed from the source count and the exposure time and corrected by a vignetting factor. The vignetting factor is derived from the exposure map as the ratio between the local and the maximum map value. However, no vignetting information could be obtained for seven observations (Chandra ObsIDs 750, 1105, 1194, 1195, 10644, 10655, and 13095) because they were performed using ACIS sub-arrays and the aimpoint is not on the used chip, meaning the maximum map value can not be obtained. The authors computed the energy conversion factor (ECF) between the count rate and flux with XSPEC using the response matrix file (RMF) of the chip center, assuming Galactic absorption and a power-law spectrum with a photon index Gamma = 1.7, which is generally adopted for Chandra sources.

The FmaxX/FminX ratio of the source over all of its detections. This is an extreme variability indicator, with FmaxX as the maximum 0.3-8.0 8 keV flux of all detections, and FminX as the minimum flux of all detections or upper limits. The ratio is set to unity without any quoted errors if FmaxX equals FminX.

The lower uncertainty in the FmaxX/FminX ratio of the source over all of its detections.

The upper uncertainty in the FmaxX/FminX ratio of the source over all of its detections.

The maximum detection significance for the X-ray source. The CIAO wavelet detection algorithm called wavdetect was run on each on-axis chip with scales of 1, 2, 4, and 8 arcsecond pixels in the 0.3-8.0 keV band, with one normalized background created simultaneously. The significance threshold was set to 10-6, which is equivalent to one possibly spurious pixel in one CCD.

The maximum background-corrected photon counts found for the X-ray source among its individual detections. The methodology for computing the photon counts for the sources is discussed in Section 2.3 of the reference paper.

The statistics for the X-ray spectral characterization of the various detections of the X-ray source, using the so-called SSS/QSS/Hard/Dim classification of the X-ray source. Many galaxies house a significant population of very soft X-ray sources, including super-soft sources (SSSs) and quasi-soft sources (QSSs), the nature of which sources is still in question. Di Stefano & Kong (2003, ApJ, 592, 884) employed strict hardness ratio (HR) criteria to identify SSSs using three energy bins to define HRs: soft (0.1-1.1 keV), medium (1.1-2.0 keV) and hard (2-7 keV). In this paper, the photon counts were calculated using the same energy bands, and the hierarchical classification scheme (Di Stefano & Kong 2003, astro-ph 0311374) was used to classify whether a source is SSS, QSS, hard, or dim (i.e., less than 10 counts). In total, about 0.6%, 6.6%, 71.3%, and 21.5% of all detected sources are classified as SSS, QSS, hard, and dim, respectively. Thus, for example, 's1' means the source had a hardness ratio like an SSS in one observation, 'q2' means the HR was like a QSS in two observations, 'h3' means the spectrum was hard in three observations, and 'd4' means it was too dim (below 10 counts) to characterize in four observations. To summarize:

      sN = number (N) of observations in SSS phase;
      qN = number (N) of observations in QSS phase;
      hN = number (N) of observations in hard phase;
      dN = number (N) of observations in dim (< 10 counts) phase.

The statistics for variability of the X-ray source during individual observations using the K-S criterion. For example, 'v:2' means the source was regarded as variable, (i.e., PK-S < 0.01, counts > 10), in 2 observations.

The authors' classification of the source using the scheme shown below:

   ULX   = Ultraluminous X-ray sources with observed LX (0.3-8 keV) in excess
            of 2*1039 erg/s;
   EULX  = Maximum LX >= 1040 erg/s;
   1ULX  = ULX inside D25 isophotes;
   1EULX = EULX inside D25 isophotes;
   2ULX  = ULX between D25 and 2*D25 isophotes, without nuclear
            sources excluded;
   2EULX = EULX between D25 and 2*D25 isophotes, without nuclear
            sources excluded;
    ULS = Ultraluminous supersoft sources with at least one SSS phase in
            which LX (0.3-8 keV) exceeds 2*1038 erg/s
            (Liu 2011, ApJS, 192, 10).

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Last Modified: Wednesday, 08-Mar-2017 13:25:16 EST