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CG 12 Chandra X-Ray Point Source Catalog
The mysterious high Galactic latitude cometary globule CG 12 has been observed with the ACIS detector on board the Chandra X-Ray Observatory. 128 X-ray sources are detected, of which half are likely young stars formed within the globule's head. This new population of >~ 50 T Tauri stars and one new embedded protostar is far larger than the previously reported few intermediate-mass and two protostellar members of the cloud. Most of the newly discovered stars have masses of 0.2-0.7 M<sub>solar</sub>, and 9% - 15% have K-band excesses from inner protoplanetary disks. X-ray properties provide an independent distance estimate consistent with the unusual location of CG 12 >~200 pc above the Galactic plane. The star formation efficiency in CG 12 appears to be 15% - 35%, far above that seen in other triggered molecular globules. The median photometric age found for the T Tauri population, assuming Siess et al. (2000, A&A, 358, 593) isochrones, is ~4 Myr with a large spread of <1 - 20 Myr and ongoing star formation in the molecular cores. The stellar age and spatial distributions are inconsistent with a simple radiation-driven implosion (RDI) model and suggest either that CG 12 is an atypically large shocked globule or that it has been subject to several distinct episodes of triggering and ablation. In their paper the authors report a previously unnoticed group of B-type stars northwest of CG 12 that may be the remnants of an OB association that produced multiple supernova explosions that could have shocked and ablated the cloud over a 15 - 30 Myr period. HD 120958 (B3e), the most luminous member of the group, may be currently driving an RDI shock into the CG 12 cloud. The current project combines four X-ray observations of the globule: <pre> Field ObsID Start Time Expo. R.A. Decl. Roll Angle (UT) (ks) (J2000.0) (deg) I.... 6423 2006 Apr 15 16:19:17 30.8 13 57 44.52 39 58 48.31 11.5 II... 6424 2006 Jun 02 07:25:09 3.1 13 57 42.87 39 43 01.76 285.0 III.. 6425 2006 Apr 13 08:44:08 3.1 13 56 19.40 39 42 47.94 14.7 IV... 6426 2006 Apr 15 12:54:20 3.1 13 56 19.40 39 58 48.09 11.1 </pre> where the units of right ascension are hours, minutes, and seconds, and the units of declination are degrees, arcminutes, and arcseconds, ObsID values are from the Chandra Observation Catalog, exposure times are the sum of Good Time Intervals (GTIs) for the CCD at the telescope aim point (CCD3) minus 1.3% to account for CCD readouts, and the aim points and roll angles are obtained from the satellite aspect solution before astrometric correction was applied. There is one primary field (I in Fig. 1 of the reference paper) with ~31 ks exposure directed at the globule's core and three secondary fields (II, III, and IV in Fig. 1) with ~3 ks exposures positioned contiguously to the north and west of the core. The primary pointing is intended to detect the population of pre-main sequence (PMS) stars forming in the molecular head of the globule. The secondary pointings are designed to locate an older population of stars expected if the present cloud is only the ablated remnant of a larger cloud that experienced sequential star formation triggering events, similar to the sequence of stars found in the authors' Chandra study of IC 1396N (Getman et al. 2007, ApJ, 654, 316, available in Browse as the IC1396NCXO table). Source searching was performed with data images and exposure maps constructed at three spatial resolutions (0.5", 1.0", and 1.4" pixel<sup>-1</sup>) using the CIAO wavdetect tool. The authors ran wavdetect with a low threshold P = 10<sup>-5</sup>, which is highly sensitive but permits false detections at this point in the analysis. This was followed by visual examination to locate other candidate sources, mainly close doubles and candidate sources near the detection threshold. Using ACIS Extract, photons were extracted within polygonal contours of ~90% encircled energy using position-dependent models of the PSF. The background was measured locally in
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IC 1396N Chandra X-Ray Point Source Catalog
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The IC 1396N cometary globule (CG) within the large nearby HII region IC 1396 has been observed with the Advanced CCD Imaging Spectrometer (ACIS) detector on board the Chandra X-Ray Observatory on 2004 October 16.93 to 17.30. 117 X-ray sources are detected, of which ~ 50-60 are likely members of the young open cluster Trumpler 37 dispersed throughout the HII region, and 25 are associated with young stars formed within the globule. Infrared photometry (2MASS and Spitzer) shows that the X-ray population is very young: 3 older Class III stars, 16 classical T Tauri stars, and 6 protostars including a Class 0/I system. The authors infer a total T Tauri population of ~ 30 stars in the globule, including the undetected population, with a star formation efficiency of 1%-4%. An elongated source spatial distribution with an age gradient oriented toward the exciting star is discovered in the X-ray population of IC 1396N, supporting similar findings in other cometary globules. The geometric and age distribution is consistent with the radiation-driven implosion (RDI) model for triggered star formation in CGs by H II region shocks. The authors include only results arising from the imaging array (ACIS-I) of four abutted 1024 x 1024 pixel front-side illuminated CCDs covering about 17' x 17' on the sky. The aim point of the array was R.A. = 21h40m42.4s, Dec. = +58d1609.7" (J2000.0) or (l,b) = (100.0, + 4.2), and the satellite roll angle (i.e., orientation of the CCD array relative to the north-south direction) was 245.9 degrees. The total net exposure time of the observation is 30 ks with no background flaring due to solar activity or data losses. This table was created by the HEASARC in February 2009 based on the electronic version of Tables 1 and 2 from the paper which were obtained from the CDS (their catalog J/ApJ/654/316 files table1.dat and table2.dat). This is a service provided by NASA HEASARC .
NGC 6334 Chandra X-Ray Point Source Catalog
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The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, has not been well sampled in past studies. The authors have analyzed a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95% of these are expected to be cluster members, most lower mass pre-main-sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20,000 - 30,000 pre-main-sequence stars. The X-ray sources show a complicated spatial pattern with ~10 distinct star clusters. The heavily obscured clusters are mostly associated with previously known far-infrared sources and radio H II regions. The lightly obscured clusters are mostly newly identified in the X-ray images. Dozens of likely OB stars are found, both in clusters and dispersed throughout the region, suggesting that star formation in the complex has proceeded over millions of years. A number of extraordinarily heavily absorbed X-ray sources are associated with the active regions of star formation. This table was created by the HEASARC in August 2009 based on the electronic version of table 1 from the above reference which were obtained from the AJ web site. This is a service provided by NASA HEASARC .
NGC 2024 Chandra X-Ray Point Source Catalog
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The NGC 2024 Chandra X-Ray Point Source Catalog contains the results of a sensitive 76 ks Chandra observation of the young stellar cluster in NGC 2024, lying at a distance of ~415 pc in the Orion B giant molecular cloud. Previous infrared observations have shown that this remarkable cluster contains several hundred embedded young stars, most of which are still surrounded by circumstellar disks. Thus, it presents a rare opportunity to study X-ray activity in a large sample of optically invisible protostars and classical T Tauri stars (CTTSs) undergoing accretion. Chandra detected 283 X-ray sources, of which 248 were identified with counterparts at other wavelengths, mostly in the near-infrared. Astrometric registration of Chandra images against the Two Micron All Sky Survey (2MASS) resulted in positional offsets of ~0.25" near field center, yielding high confidence identifications of infrared counterparts. The Chandra detections are characterized by hard, heavily absorbed spectra and specular variability. Spectral analysis of more than 100 of the brightest X-ray sources yields a mean V-band extinction of ~10.5 magnitudes and typical plasma energies ~ 3 keV. Chandra detected all but one of a sample of 27 classical T Tauri stars (CTTSs) identified from previous near- and mid-infrared photometry, and their X-ray and bolometric luminosities are correlated. IRS 2b, which is thought to be a massive embedded late O or early B star that may be the ionizing source of NGC 2024, is detected as an X-ray source. Seven millimeter-bright cores (FIR 1-7) in NGC 2024 that may be protostellar were not detected, with the possible exception of faint emission near the unusual core FIR 4. This table was created by the HEASARC in January 2007 based on CDS table J/ApJ/598/375/table1.dat. This is a service provided by NASA HEASARC .
NGC 4649 Chandra X-Ray Point Source Catalog 2
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This table contains the main X-ray source catalog for the Chandra monitoring observations of the 16.5-Mpc distant elliptical galaxy, NGC 4649. The galaxy has been observed with Chandra ACIS-S3 in six separate pointings, reaching a total exposure of 299 ks. There are 501 X-ray sources detected in the 0.3-8.0 keV band in the merged observation or in one of the six individual observations; 399 sources are located within the D25 ellipse. The observed 0.3-8.0 keV luminosities of these 501 sources range from 9.3 x 1036 erg s-1 to 5.4 x 1039 erg s-1. The 90% detection completeness limit within the D25 ellipse is 5.5 x 1037 erg s-1. Based on the surface density of background active galactic nuclei (AGNs) and the detection completeness, we expect ~ 45 background AGNs among the catalog sources (~ 15 within the D25 ellipse). There are nine sources with luminosities greater than 1039 erg s-1, which are candidates for ultraluminous X-ray sources. The nuclear source of NGC 4649 is a low-luminosity AGN, with an intrinsic 2.0-8.0 keV X-ray luminosity of 1.5 x 1038 erg s-1. The X-ray colors suggest that the majority of the catalog sources are low-mass X-ray binaries (LMXBs). The authors find that 164 of the 501 X-ray sources show long-term variability, indicating that they are accreting compact objects, and discover four transient candidates and another four potential transients. They also identify 173 X-ray sources (141 within the D25 ellipse) that are associated with globular clusters (GCs) based on Hubble Space Telescope and ground-based data; these LMXBs tend to be hosted by red GCs. Although NGC 4649 has a much larger population of X-ray sources than the structurally similar early-type galaxies, NGC 3379 and NGC 4278, the X-ray source properties are comparable in all three systems. This HEASARC table contains the main Chandra source catalog of the basic properties of the 501 X-ray detected sources (Table 3 in the reference paper which includes both sources detected in the merged X-ray image as well as a number only detected in the individual observations), and also the information on source counts, hardness ratios and soft and hard X-ray colors in the merged observation for the same 501 X-ray detected sources (Table 4 in the reference paper). It does not contain the information on source counts, hardness ratios and soft and hard X-ray colors for these same sources in the six individual observations that were contained in Tables 5 - 10 of the reference paper. This table was created by the HEASARC in March 2013 based on the electronic version of Tables 3 and 4 from the reference paper which were obtained from the ApJS website.. This is a service provided by NASA HEASARC .
NGC 4278 Chandra X-Ray Point Source Catalog
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This table lists some of the properties of the discrete X-ray sources detected in the authors' monitoring program of the globular cluster (GC)-rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate pointings, resulting in a co-added exposure of 458 ks. From this deep observation, 236 sources have been detected within the region overlapped by all observations, 180 of which lie within the D25 ellipse angular diameter of the galaxy. These 236 sources range in X-ray luminosity LX from 3.5 x 1036 erg s-1 (with 3-sigma upper limit <= 1 x 1037 erg s-1) to ~2 x 1040 erg s-1, including the central nuclear source which has been classified as a LINER. From optical data, 39 X-ray sources have been determined to be coincident with a GC, these sources tend to have high X-ray luminosity, with 10 of these sources exhibiting LX > 1 x 1038 erg s-1. From X-ray source photometry, it has been determined that the majority of the 236 point sources that have well-constrained colors have values that are consistent with typical low-mass X-ray binary spectra, with 29 of the sources expected to be background objects from the log N-log S relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Three of these sources have been identified as transient candidates, with a further three possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy. This HEASARC table contains the master source list (Table 3 of the reference paper) and the X-ray properties of the sources in the co-added observations (Table 4 of the reference paper), but not the X-ray properties of the sources in the 6 individual observations (Tables 5-10 of the reference paper). The details of the six individual pointings used in this study, e.g., the Chandra ObsIDs, dates, exposure times and cleaned exposure times, are given in Table 1 of the reference paper, and repeated here:
 Obs. No.OBSID Date Exposure (s) Cleaned Exposure (s) 1 4741 2005 Feb 3 37462.0 37264.5 2 7077 2006 Mar 16 110303.8 107736.7 3 7078 2006 Jul 25 51433.2 48076.2 4 7079 2006 Oct 24 105071.7 102504.6 5 7081 2007 Feb 20 110724.0 107564.5 6 7080 2007 Apr 20 55824.8 54837.5 Total Co-added 470819.5 457984.0 
Notes. The pointing OBSID 7181 was taken before OBSID 7080, so to maintain the time sequence of the exposures these observation numbers have been labeled as above in the reference paper. The details of the energy bands and X-ray colors used in this study are given in Table 2 of the reference paper, and repeated here:
 Band/Color Energy Range/Definition Broad (B) 0.3-8 keV Soft (S) 0.3-2.5 keV Hard (H) 2.5-8 keV Soft 1 (S1) 0.3-0.9 keV Soft 2 (S2) 0.9-2.5 keV Conventional broad (Bc) 0.5-8 keV Conventional soft (Sc) 0.5-2 keV Conventional hard (Hc) 2-8 keV Hardness ratio HR (Hc-Sc)/(Hc+Sc) X-ray color C21 -log(S2) + log(S1) = log(S1/S2) X-ray color C32 -log(H) + log(S2) = log(S2/H) 
This table was created by the HEASARC in April 2009 based on machine-readable versions of Tables 3 and 4 from the reference paper which were obtained from the ApJ web site. This is a service provided by NASA HEASARC .
NGC 2237 Chandra X-Ray Point Source Catalog
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The authors have obtained high spatial resolution Chandra X-ray images of the NGC 2237 young stellar cluster on the periphery of the Rosette Nebula. They detect 168 X-ray sources, 80% of which have stellar counterparts in USNO, Two Micron All Sky Survey, and deep FLAMINGOS images. These constitute the first census of the cluster members with 0.2 <~ M <~ 2 Msun. Star locations in near-infrared color-magnitude diagrams indicate a cluster age of around 2 Myr with a visual extinction of 1 <~ AV <~ 3 at 1.4 kpc, the distance of the Rosette Nebula's main cluster NGC 2244. The authors derive the K-band luminosity function and the X-ray luminosity function of the cluster, which indicate a population of ~ 400-600 stars. The X-ray-selected sample shows a K-excess disk frequency of 13%. The young Class II counterparts are aligned in an arc ~3 pc long suggestive of a triggered formation process induced by the O stars in NGC 2244. The diskless Class III sources are more dispersed. Several X-ray emitting stars are located inside the molecular cloud and around gaseous pillars projecting from the cloud. These stars, together with a previously unreported optical outflow originating inside the cloud, indicate that star formation is continuing at a low level and the cluster is still growing. This X-ray view of young stars on the western side of the Rosette Nebula complements the authors' earlier studies of the central cluster NGC 2244 and the embedded clusters on the eastern side of the Nebula. The large-scale distribution of the clusters and molecular material is consistent with a scenario in which the rich central NGC 2244 cluster formed first, and its expanding H II region triggered the formation of the now-unobscured satellite clusters Rosette Molecular Cloud (RMC) XA and NGC 2237. A large swept-up shell of material around the H II region is now in a second phase of collect-and-collapse fragmentation, leading to the recent formation of subclusters. Other clusters deeper in the molecular cloud appear unaffected by the Rosette Nebula expansion. Some sources which have information from published catalogs are listed by their source_number value below, where for convenience, [OI81] = Ogura & Ishida (1981, PASJ, 33, 149), [MJD95] = Massey, Johnson, & Degioia-Eastwood (1995, ApJ, 454, 151) and [BC02] = Berghofer & Christian (2002, A&A, 384, 890):
 53 = [OI81] 14 = [MJD95] 104; spectral type B1V; pmRA=11.0 mas/yr, pmDE=-2.8 mas/yr; 54 = [OI81] 10 = [MJD95] 108; spectral type B2V; pmRA=-2.3 mas/yr, pmDE=-11.9 mas/yr; 61 = V539 Mon [OI81] 13 = [MJD95] 110; MSX6C G206.1821-02.3456; pmRA=2.8 mas/yr, pmDE=0.4 mas/yr; 71 = [OI81] 12 = [MJD95] 102; pmRA=6.8 mas/yr, pmDE=0.6 mas/yr; 128 = [OI81] 35 = [MJD95] 471; spectral type A2:; pmRA=-0.8 mas/yr, pmDE=3.6 mas/yr; 138 = [OI81] 36 = [MJD95] 497; spectral type B5; pmRA=6.5 mas/yr, pmDE=2.1 mas/yr; 141 = [MJD95] 498; pmRA=-3.0 mas/yr, pmDE=1.9 mas/yr; 149 = [BC02] 11; known X-ray source; log(Lx(ROSAT/PSPC))=31.01 erg/s; pmRA=0.6 mas/yr, pmDE=-12.6 mas/yr; 161 = [MJD95] 653; pmRA=-1.0 mas/yr, pmDE=-5.4 mas/yr 
This table was created by the HEASARC in July 2010 based on electronic versions of Tables 1, 2, 3 and 4 of the reference paper which were obtained from the electronic ApJ web site. To distinguish between the 130 X-ray sources in the primary sample (Table 1 of the reference paper) and the 38 X-ray sources in the tentative sample (Table 2 of the reference paper), the HEASARC has created a parameter called source_sample which is set to 'P' for the primary sources and to 'T' for the tentative sources. This is a service provided by NASA HEASARC .
M 33 Chandra X-Ray Point Source Catalog
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NGC 6357 Chandra X-Ray Point Source Catalog
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This contains some of the results from the first high spatial resolution X-ray study of the massive star-forming region NGC 6357, which were obtained in a 38 ks Chandra/ACIS observation. Inside the brightest constituent of this large H II region complex is the massive open cluster Pismis 24. It contains two of the brightest and bluest stars known, yet remains poorly studied; only a handful of optically bright stellar members have been identified. The authors have investigated the cluster extent and initial mass function and detected ~800 X-ray sources with a limiting sensitivity of ~ 1030 erg s-1: this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster, increasing the number of known members from optical studies by a factor of ~ 50. The high-luminosity end (log L[2-8 keV] >= 30.3 erg s-1) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power-law relation as seen in the Orion Nebula Cluster and Cepheus B, yielding the first estimate of NGC 6357's total cluster population, a few times the known Orion population. The long-standing LX ~ 10-7 Lbol correlation for O stars is confirmed. Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented. Many cluster members are estimated to be intermediate-mass stars from available infrared photometry (assuming an age of ~ 1 Myr), but only a few exhibit K-band excess. The authors report the first detection of X-ray emission from an evaporating gaseous globule at the tip of a molecular pillar; this source is likely a B0-B2 protostar. NGC 6357 was observed on 2004 July 9 with the Imaging Array of the Advanced CCD Imaging Spectrometer (ACIS-I) on board Chandra. Four front-illuminated (FI) CCDs form the ACIS-I, which covers a field of view (FOV) of ~ 17 by 17 arcminutes. The observation was made in the standard Timed Exposure, Very Faint mode, with 3.2 s integration time and 5 pixel by 5 pixel event islands. The total exposure time was 38 ks and the satellite roll angle was 289 degrees. The aim point was centered on the O3 If star Pis 24-1, the heart of the OB association Pismis 24. The Chandra observation ID is 4477. Data reduction started with filtering the Level 1 event list processed by the Chandra X-ray Center pipeline to recover an improved Level 2 event list. To improve absolute astrometry, X-ray positions of ACIS-I sources were obtained by running the wavdetect wavelet-based source detection algorithm within the Chandra Interactive Analysis of Observations (CIAO) package on the original Level 2 event list, using only the central 8 by 8 arcminutes of the field. The resulting X-ray sources were matched to the 2MASS point source catalog. The authors calculated the position offsets between 277 X-ray sources and their NIR counterparts and applied an offset of +0.02" in right ascension (R.A.) and -0.33" in declination to the X-ray coordinates. From an initial list of 910 potential X-ray sources, the authors rejected sources with a PB > 1% likelihood of being a background fluctuation. The trimmed source list includes 779 sources, with full-band (0.5 - 8.0 keV) net (background-subtracted) counts ranging from 1.7 to 1837 counts. The 779 valid sources were purposely divided by the authors into two lists: the 665 sources with PB < 0.1% make up the primary source list of highly reliable sources (Table 1 in the reference paper; sources with source_type = 'M' in this table), and the remaining 114 sources with PB >= 0.1% likelihood of being spurious background fluctuations were listed as tentative sources in Table 2 of the reference paper (source_type = 'T' in this table). The authors believe that most of these tentative sources are likely real detections. This table was created by the HEASARC in October 2007 based on the merger of the electronic versions of Tables
M 51 Chandra X-Ray Discrete Source Catalog
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NGC 6530 Chandra X-Ray Point Source Catalog
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In a deep 60 ks Chandra ACIS-I X-ray observation of the very young (~ 1.5 - 2.0 Myr) cluster NGC 6530 on 2001 Jun 18-19, the authors have detected 884 X-ray point sources and argue that a very large fraction of them (90%-95%) must be pre-main-sequence (PMS) cluster members, mostly low-mass stars. This is a significant enlargement of the known NGC 6530 stellar population with respect to previous optical studies, including H-alpha surveys. They identify 220 X-ray sources with catalogued stars down to V = 17, while most unidentified sources have fainter counterparts. Moreover, they find an infrared counterpart in the 2MASS (CDS. No. ) Catalog for 731 X-ray sources. The optically identified cluster X-ray sources are found in a band in the H-R diagram above the main sequence, in the locus of 0.5 - 1.5 Myr PMS stars, with masses down to 0.5 - 1.5 solar masses (M_sun). The pointing direction for the Chandra observation was the NGC 6530 cluster center at RA = 18^h 04^m 24.38^s, Dec = -24^o 21' 05.8" (J2000.0). The PWDetect algorithm found 884 X-ray point sources in the ACIS-I image above a detection significance threshold chosen to ensure only 1 spurious detection on the average. The Sung et al. (2000, AJ, 120, 333; CDS Cat. ) = SCB Catalog of optical objects against which the X-ray point source list was compared doed not cover the easternmost 2.25' of the ACIS FOV (RAs later than 18^h 04^m 52^s), notice, which comprises about 13% of the ACIS FOV. There are 46 detected X-ray sources (5.2% of the total) in the area not covered by the SCB Catalog. A matching distance of 4 times the X-ray error radius or 2.0" (whichever is greater) was used to identify optical counterparts to the X-ray sources, after a systematic shift between the X-ray and optical positions of -0.4" and 1.84" in RA and declination, respectively, was applied. The authors estimate that as many as 28 of their 220 optical identifications may be spurious, preferentially those in the outer parts of the FOV where the positional uncertainties are larger. There are 8792 'good' 2MASS sources in the ACIS FOV. A matching distance of 4 times the X-ray error radius or 1.5" (whichever is greater) was used to identify 2MASS counterparts to the X-ray sources, after systematic corrections of 0.3" and 1.75" in RA and declination, respectively, were applied to the 'raw' X-ray positions. There are 13 cases where there are two possible IR counterparts to a single X-ray source, and 2 cases where there are three possible IR Counterparts to a single X-ray source. (Notice that, in such cases, this table contains multiple entries, one for each counterpart, and hence there are 901 entries compared to 884 X-ray sources.) The authors conclude that the plausible number of spurious X-ray-2MASS identifications is between 30 and 50. Overall, there remain 146 X-ray sources with no optical or IR identification. This table was created by the HEASARC in December 2006 based on CDS table J/ApJ/608/781, the file table1.dat. This is a service provided by NASA HEASARC .