- ID:
- ivo://nasa.heasarc/champpsc
- Title:
- Chandra Multiwavelength Project (ChaMP) Point Source Catalog
- Short Name:
- ChaMPPS
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table represents the `Main Chandra Multiwavelength Project (ChaMP) X-Ray Point Source Catalog' and contains the basic parameters, photometry, and fluxes of 6512 ChaMP sources in 130 Chandra observations from Chandra Cycles 1 and 2. This table lists fluxes for 2 assumed spectral energy distributions with the photon indices of Gamma=1.4 and Gamma=1.7. This catalog was distributed by the ChaMP team based on the "Chandra Multiwavelength Project: X-ray Point Source Catalog (Kim et al., 2007, ApJS, 169, 401)", and was downloaded from <a href="http://hea-www.harvard.edu/CHAMP/">http://hea-www.harvard.edu/CHAMP/</a>. If you have any comments/questions on this catalog, please contact mkim @ cfa.harvard.edu or dkim @ cfa.harvard.edu. The full Chandra Multiwavelength Project (ChaMP) X-ray point source catalog lists ~ 6800 X-ray sources detected in 149 Chandra observations covering ~ 10 square degrees. The full ChaMP catalog sample is 7 times larger than the initial published ChaMP catalog (Kim et al. 2004, ApJS, 150, 19). The exposure times of the fields in this sample range from 0.9 to 124 ks, corresponding to a deepest X-ray flux limit in the 0.5 - 8.0 keV band of 9 x 10<sup>-16</sup> ergs cm<sup>-2</sup> s<sup>-1</sup>. The ChaMP X-ray data were uniformly reduced and analyzed with ChaMP-specific pipelines and then carefully validated by visual inspection. The ChaMP catalog includes X-ray photometric data in eight different energy bands as well as X-ray spectral hardness ratios and colors, source reliability, detection probability, and positional uncertainties. The false source detection rate is ~1% of all detected ChaMP sources, while the detection probability is better than ~ 95% for sources with counts >~ 30 and off-axis angle <5'. The typical positional offset between ChaMP X-ray source and their SDSS optical counterparts is 0.7" +/- 0.4", derived from ~ 900 matched sources. This HEASARC table contains the main ChaMP catalog of 6512 X-ray point sources in 130 ChaMP fields observed once and in the overlapping fields which had the longest exposures. It does not contain the supplementary ChaMP catalog of 853 sources in 19 ChaMP overlapping fields with shorter exposure times. This table was created by the HEASARC in October 2006 based on the table <a href="http://hea-www.cfa.harvard.edu/CHAMP/IMAGES_DATA/champ_xpc.tab">http://hea-www.cfa.harvard.edu/CHAMP/IMAGES_DATA/champ_xpc.tab</a> on the ChaMP website. This is a service provided by NASA HEASARC .
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- ID:
- ivo://nasa.heasarc/chpngptsrc
- Title:
- Chandra Nearby Galaxies Point Source Catalog
- Short Name:
- ChanNGalPSC
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The authors have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies. The properties (e.g., counts in 3 energy bands, hardness ratios and inferred X-ray luminosities) of the 1441 X-ray point sources that were detected in these galaxies are listed in this table. The total point-source X-ray (0.3 - 8.0 keV) luminosity L<sub>XP</sub> is found to be well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies, and is well correlated with the B-band and K-band luminosities of elliptical galaxies. This suggests an intimate connection between L<sub>XP</sub> and both the old and the young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass and the star formation rate (SFR). This table was created by the HEASARC in October 2006 based on CDS table J/ApJ/602/231/tablea1.dat This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/channsgpsc
- Title:
- Chandra Nearby Spiral Galaxies Point Source Catalog
- Short Name:
- ChanNSPiral
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- Emission from discrete point sources dominates the X-ray luminosity in spiral galaxies. This table contains the results from a survey of 11 nearby, nearly face-on spiral galaxies observed with the Chandra X-ray Observatory in 22 observations for a total of 869 ks. The galaxies in this sample are at high Galactic latitude to minimize the absorbing column in the line of site, are nearby to minimize source confusion, and span the Hubble sequence for spirals (types 0-7), allowing insights into the X-ray source population of many diverse systems. More than 820 unique point sources are detected in at least one observation within the D25 ellipses of the galaxies. A minimum of 27% of the sources exhibit detectable long- or short-term variability, indicating a source population dominated by accreting XRBs. 17 ultraluminous X-ray sources are detected, with typical rates per galaxy of 1 or 2. In this table, source lists for the 11 galaxies are presented, along with source counts, fluxes, luminosities, X-ray colors, and variability properties. It should be noted that the X-ray source counts presented in this table are raw, background-subtracted counts, so the count rates in sources from the same galaxy that fall on different CCDs cannot be directly compared. The colors presented have been corrected for the differences between front-illuminated and back-illuminated CCDs. This table was created by the HEASARC in November 2006 based on the electronic version of Table 4 obtained from the electronic ApJ web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/coup
- Title:
- Chandra Orion Ultradeep Point Source Catalog
- Short Name:
- ChandraOUP
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Chandra Orion Ultradeep Project (COUP) was a deep observation of the Orion Nebula Cluster (ONC) that was obtained with the Chandra X-Ray Observatory's Advanced CCD Imaging Spectrometer (ACIS). This Browse table contains the COUP catalog of more than 1600 X-ray point sources that were detected in the exceptionally deep 2003 January observation, which was an 838 ks exposure made over a continuous period of 13.2 days. The COUP observation provides the most uniform and comprehensive data set on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy. This table was created by the HEASARC in September 2006 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/160/319">CDS catalog J/ApJS/160/319</a>, tables 2, 4, 6, 7, 8, 9, and 10. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/gcptsrccxo
- Title:
- Chandra Point Sources in 18 Distant Galaxy Clusters
- Short Name:
- GCPTSRCCXO
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- With the superb angular resolution of the Chandra Observatory, it is now possible to detect X-ray point sources, either embedded in galaxy clusters or along the cluster line of sight, which could not be resolved by previous instruments. This now allows studies of source counts in distant cluster fields. The authors want to analyze the inner region of clusters of galaxies to check for the presence of any over-density of X-ray point sources embedded in the gas diffuse emission. These point sources are possible AGN belonging to the clusters and could contaminate the cluster emission. The authors used a sample of 18 distant (0.25 < z < 1.01) galaxy clusters from the Chandra archive to construct the log N - log S relation, in both the soft and hard energy bands, for the X-ray point sources detected in the central cluster region to be compared with the counts of point sources detected in similarly deep fields without clusters. The authors find a ~2-sigma excess of cluster region sources at the bright end of the log N - log S distribution. The radial distribution of the brightest X-ray point sources confirms this excess and indicates that it is confined to the inner 0.5 Mpc of the cluster region. The results suggest the possible existence of X-ray sources belonging to the cluster (most probably AGN, given their 0.5-10 keV luminosity ranging from 10<sup>43</sup> to 10<sup>44</sup> erg s<sup>-1</sup>): on average one every three clusters. Unlike previous studies, which have mainly investigated the point-source population in the vicinity of the galaxy clusters, the present study analyzes the content of point sources within the 1 Mpc region covered by the cluster extent. This work confirms the findings of other investigators who analyzed the central 1 Mpc region of more massive clusters and/or groups in a similar redshift range. The X-ray source excess found here is much smaller than the excess of radio galaxies found recently in high-z X-ray selected clusters, possibly due to the better sensitivity of the radio observations. The properties of the clusters and of the Chandra exposures in which they were observed are given in Table 1 of the reference paper, and are reproduced below: <pre> Cluster Name z RA (J2000) Dec ObsID ACIS Mode Exp N_H L_sb L_hb h m s d ' " ks [units are below] Abell 2125 0.246 15 41 12 +66 16 01 2207 I VF 79.7 2.77 0.13 0.56 ZW CL 1454.8+2233 0.258 14 57 15 +22 20 33 4192 I VF 91.4 3.22 0.23 0.74 MS 1008.1-1224 0.302 10 10 32 -12 39 23 926 I VF 44.2 6.74 0.44 1.57 ZW CL 0024.0+1652 0.394 00 26 35 +17 09 39 929 S VF 36.7 4.19 0.34 2.22 MS 1621.5+2640 0.426 16 23 36 +26 34 21 546 I F 30.0 3.59 0.81 3.41 RXJ 1701.3+6414 0.453 17 01 24 +64 14 10 547 I VF 49.5 2.59 0.64 2.67 CL 1641+4001 0.464 16 41 53 +40 01 46 3575 I VF 44.0 1.02 0.67 2.62 V 1524.6+0957 0.516 15 24 40 +09 57 48 1664 I VF 49.9 2.92 0.89 3.29 MS 0451.6-0305 0.539 04 54 12 -03 00 53 902 S F 41.5 5.18 0.73 4.12 V 1121+2327 0.562 11 20 57 +23 26 27 1660 I VF 66.9 1.30 0.73 3.00 MS 2053.7-0449 0.583 20 56 21 -04 37 51 1667 I VF 43.5 4.96 1.32 4.91 V 1221+4918 0.700 12 21 26 +49 18 30 1662 I VF 79.4 1.44 1.18 4.62 MS 1137.5+6625 0.782 11 40 22 +66 08 18 536 I VF 117.5 1.18 0.81 4.04 RDCSJ 1317+2911 0.805 13 17 21 +29 11 19 2228 I VF 111.3 1.04 0.85 3.59 RDCSJ 1350+6007 0.805 13 50 48 +60 06 54 2229 I VF 58.3 1.76 1.77 7.26 RXJ 1716.4+6708 0.813 17 16 49 +67 08 26 548 I F 51.5 3.71 2.17 9.45 MS 1054.4-0321 0.830 10 56 59 -03 37 37 512 S F 67.5 3.67 1.07 6.61 WARPJ 1415.1+3612 1.013 14 15 11 +36 12 00 4163 I VF 89.2 1.10 1.93 7.54 </pre> where Exp is the Chandra exposure time in ks corresponding to the nominal exposure filtered to exclude time periods of high background, N_H is the Galactic hydrogen column density in the direction of the cluster of galaxies, in units of 10<sup>20</sup> cm<sup>-2</sup>, and L_sb and L_hb are the limiting luminosities in units of 10<sup>42</sup> erg s<sup>-1</sup> for point sources in the clusters in the 0.5-2.0 keV and 2-10 keV energy bands, respectively. This table was created by the HEASARC in September 2010 based on the electronic version of Table 2 from the reference paper which was obtained from the CDS, their catalog J/A+A/462/449. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/chansexsi
- Title:
- Chandra Serendipitous Extragalactic X-Ray Source ID (SEXSI) Catalog
- Short Name:
- Chan/Seren/ID
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) program is designed to extend greatly the sample of identified extragalactic hard X-ray (2 - 10 keV) sources at intermediate fluxes (~10<sup>-13</sup> to 10<sup>-15</sup> erg/cm<sup>2</sup>/s). SEXSI, which studies sources selected from more than 2 deg<sup>2</sup>, provides an essential complement to the Chandra Deep Fields, which reach depths of 5 x 10<sup>-16</sup> erg/cm<sup>2</sup>/s (2 - 10 keV) but over a total area of less than 0.2 deg<sup>2</sup>. In their published paper, the authors describe the characteristics of the survey and their X-ray data analysis methodology. They present the cumulative flux distribution for the X-ray sample of 1034 hard sources and discuss the distribution of spectral hardness ratios. Their log N -log S in this intermediate flux range connects to those found in the Deep Fields, and by combining the data sets, they constrain the hard X-ray population over the flux range in which the differential number counts change slope and from which the bulk of the 2 - 10 keV X-ray background arises. They further investigate the log N - log S distribution separately for soft and hard sources in the sample, finding that while a clear change in slope is seen for the softer sample, the hardest sources are well described by a single power law down to the faintest fluxes, consistent with the notion that they lie at lower average redshift. In the SEXSI program, fields were selected with high Galactic latitude (|b| > 20 degrees) and with declinations accessible to the optical facilities available to the authors (declination > -20 degrees). They used observations taken with Chandra's Advanced Camera for Imaging Spectroscopy (ACIS I- and S-modes; Bautz et al., 1998, Proc. SPIE, 3444, 210) only (for sensitivity in the hard band). All the fields presented in this paper have data that are available in the Chandra public archive. This table was created by the HEASARC in June 2004 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/596/944/table4">CDS Catalog J/ApJ/596/944/table4</a>.dat which is a representation of Table 4 from the published version. Note that it does not include the Soft-Band-Only Source Catalog (Table 6 in the published version of the paper). This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/chansexagn
- Title:
- Chandra Serendipitous Extragalactic X-Ray Source ID (SEXSI)/Spitzer AGN Catalog
- Short Name:
- CHANSEXAGN
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The authors compare the relative merits of active galactic nuclei (AGN) selection at X-ray and mid-infrared wavelengths using data from moderately deep fields observed by both Chandra and Spitzer. The X-ray-selected AGN sample and associated photometric and spectroscopic optical follow-up are drawn from a subset of fields studied as part of the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program. Mid-infrared data in these fields are derived from targeted and archival Spitzer imaging, and mid-infrared AGN selection is accomplished primarily through application of the Infrared Array Camera (IRAC) color-color AGN "wedge" selection technique. Nearly all X-ray sources in these fields which exhibit clear spectroscopic signatures of AGN activity have mid-infrared colors consistent with IRAC AGN selection. These are predominantly the most luminous X-ray sources. X-ray sources that lack high-ionization and/or broad lines in their optical spectra are far less likely to be selected as AGNs by mid-infrared color selection techniques. The fraction of X-ray sources identified as AGN in the mid-infrared increases monotonically as the X-ray luminosity increases. Conversely, only 22% of mid-infrared-selected AGN are detected at X-ray energies in the moderately deep (t_exp_n~ 100 ks) SEXSI Chandra data. The authors have expanded the multi-wavelength data available for six SEXSI fields by obtaining Spitzer imaging observations. All six fields have deep Chandra X-ray images, optical imaging, and extensive, deep optical spectroscopy -- all of which has been published in Harrison et al. (2003, ApJ, 596, 944), Eckart et al. (2005, ApJS, 156, 35), and Eckart et al. (2006, ApJS, 165, 19). The authors obtained mid-infrared imaging through both archival and targeted Spitzer programs which include imaging at 3.6, 4.5, 5.8, and 8 micron (µm) from IRAC (PID 00017, 00064, 20694 and 20808), and imaging at 24 um from MIPS (PID 20808 and 00083). This table contains mid-IR photometric data for 290 hard X-ray-selected SEXSI sources. Each of the four IRAC catalogs as well as the MIPS catalog was individually matched to the SEXSI X-ray source positions using a 2.5 arcseconds search radius. To calculate a false match rate, the authors shifted the X-ray source catalog by 1' and matched to the IRAC and MIPS catalogs; this entire procedure was repeated 6 times using different 1' shifts. The resulting false match rates were 10.1% (3.6 um), 7.2% (4.5 um), 3.7% (5.8 um), 2.6% (8.0 um), 1% (24 um), and <1% for four-band-detected IRAC sources. This table was created by the HEASARC in Match 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/708/584">CDS Catalog J/ApJ/708/584</a> file table2.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/csc
- Title:
- Chandra Source Catalog, v2.0
- Short Name:
- CSC
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Chandra Source Catalog (CSC) is the definitive catalog of X-ray sources detected by the Chandra X-ray Observatory. By combining Chandra's sub-arcsecond on-axis spatial resolution and low instrumental background with consistent data processing, the CSC delivers a wide variety of uniformly calibrated properties and science ready data products for detected sources over four decades of flux. The second major release of the catalog, CSC 2.0, includes measured properties for 317,167 unique compact and extended X-ray sources in the sky, allowing statistical analysis of large samples, as well as individual source studies in the "Master Sources" table, provided herein. The extracted properties are provided for 928,280 individual observation detections, identified in 10,382 Chandra ACIS and HRC-I imaging observations released publicly through the end of 2014, at the <a href="https://cxc.harvard.edu/csc/about.html">Chandra X-ray Center</a>. CSC 2.0 includes -- as an "alpha" release -- photometric properties for 1,299 highly extended (> ~30") sources, together with surface brightness polygons for several contour levels. The sensitivity limit for compact sources in CSC 2.0 is ~5 net counts (a factor of >~2 better than the previous catalog release). This improvement is achieved by using a two-stage approach that involves co-adding multiple observations of the same field prior to source detection, and then using an optimized source detection method. For each X-ray detection and source, the catalog provides a detailed set of more than 100 tabulated positional, spatial, photometric, spectral, and temporal properties (each with associated lower and upper confidence intervals and measured in multiple energy bands). The catalog Bayesian aperture photometry code produces robust photometric probability density functions (PDFs), even in crowded fields and for low count detections. Release 2 uses a Bayesian Blocks analysis to identify multiple observations of the same source that have similar photometric properties, and these are analyzed simultaneously to improve S/N. The energy bands used to derive many of the CSC properties are defined in Table 4 of the reference paper: ultrasoft (u: 0.2-0.5 keV), soft (s: 0.5-1.2 keV), medium (m: 1.2-2.0 keV), hard (h: 2.0-7.0) and broad (b: 0.5-7.0 keV) for the ACIS energy bands, and wide (w: 0.1-10.0 keV) for the HRC energy band. The energy bands are chosen to optimize the detectability of X-ray sources while simultaneously maximizing the discrimination between different spectral shapes on X-ray color-color diagrams. Numerous source-specific catalog properties are evaluated within defined apertures. The authors define the "PSF 90% ECF aperture" for each source to be the ellipse that encloses 90% of the total counts in a model PSF centered on the source position. Because the size of the PSF is energy-dependent, the dimensions of the PSF 90% ECF aperture vary with energy band. They define the "source region aperture" for each source to be equal to the corresponding 3-sigma source region ellipse included in the merged source list, scaled by a factor of 1.5. Like the PSF 90% ECF aperture, the source region aperture is also centered on the source position, but the dimensions of the aperture are independent of energy band. This database table was ingested by the HEASARC in November 2019 and is based on a download of the online version of the Chandra Source Catalog, v2.0, at the CXC using the CLI. Refer to <a href="http://cxc.harvard.edu/csc/">http://cxc.harvard.edu/csc/</a> for details. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/chantypgpr
- Title:
- Chandra Typical Galactic Plane Region Point Source Catalog
- Short Name:
- CHANTYPGPR
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), the authors carried out a deep hard X-ray observation of the Galactic plane region at a location (l, b) ~ (28.5 degrees, 0.0 degrees), where no discrete X-ray source had been reported previously. They detected 274 new point X-ray sources (4-sigma or greater confidence in any of the 3 energy bands 0.5 - 3.0 keV, 3.0 - 8.0 keV or 0.5 - 8.0 keV), as well as strong Galactic diffuse emission within two partially overlapping ACIS-I fields (~ 250 square arcminutes in total). The point-source sensitivity was ~ 3 x 10<sup>-15</sup> ergs/s/cm<sup>2</sup> in the 2 - 10 keV band and ~ 2 x 10<sup>-16</sup> erg/s/cm<sup>2</sup> in the 0.5 - 2 keV band The sum of all the detected point-source fluxes accounts for only ~ 10% of the total X-ray flux in the field of view. Only 26 point sources were detected in both the soft and hard bands, indicating that there are two distinct classes of X-ray source distinguished by their spectral hardness ratios. The surface number density of the hard sources is only slightly higher than that measured in high Galactic latitude regions, indicating that the majority of the hard sources are background AGNs. Following up the Chandra observation, the authors performed a near-infrared (NIR) survey with SofI at ESO/NTT. Almost all the soft X-ray sources have been identified in the NIR, and their spectral types are consistent with main-sequence stars, suggesting that most of them are nearby X-ray-active stars. On the other hand, only 22% of the hard sources had near-IR counterparts, which are presumably Galactic. From X-ray and near-IR spectral study, they are most likely to be quiescent cataclysmic variables. This Browse table was created by the HEASARC in December 2006 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/635/214/">CDS Catalog J/ApJ/635/214/</a>, the file table1.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/chanvguide
- Title:
- Chandra Variable Guide Star Catalog
- Short Name:
- CHANVGUIDE
- Date:
- 07 Mar 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. The authors present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02 mag amplitude in the 4000-10000 Angstroms range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, the authors believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75,000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Future releases of VGUIDE will include newly identified variable guide stars as the mission proceeds. An important advantage of the use of space data to identify and analyze variable stars is the relatively long observations that are available. The Chandra orbit allows for observations up to 2 days in length. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper (from which this HEASARC representation was created) and as a public Web interface at <a href="http://cxc.harvard.edu/vguide/">http://cxc.harvard.edu/vguide/</a>. Light curves with data at the instrumental time resolution of about 2 s, overplotted with the data binned at 1 ks, can be viewed on the above-mentioned public Web interface and downloaded for further analysis. (This HEASARC Browse table also contains links to these light curves). VGUIDE is a unique project using data collected during the mission that would otherwise be ignored. The stars available for use as Chandra guide stars are generally 6-11 magnitudes and are commonly spectral types A and later. Due to the selection of guide stars entirely for positional convenience, this catalog avoids the possible bias of searching for variability in objects where it is to be expected. Statistics of variability compared to spectral type indicate the expected dominance of A-F stars as pulsators. Eclipsing binaries are consistently 20%-30% of the detected var iables across all spectral types. This table was created by the HEASARC in July 2010 based on the electronic version of Table 4 from the paper which was obtained from the Astrophysical Journal web site. This is a service provided by NASA HEASARC .
