OMEGCENCXO ivo://nasa.heasarc/omegcencxo NASA/GSFC HEASARC Haggard et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source The authors analyzed a ~ 70 ks Chandra Advanced CCD Imaging Spectrometer (ACIS) exposure of the globular cluster Omega Cen (NGC 5139). The ~ 17' x 17' field of view fully encompasses three cluster core radii and almost twice the half-mass radius. They detected 180 sources to a limiting flux of ~ 4.3 x10 <sup>-16</sup> erg/cm<sup>2</sup>/s (L<sub>x</sub> = 1.2 x 10<sup>30</sup> erg/s at the 4.9 kpc distance to the cluster). After accounting for the number of active galactic nuclei and possible foreground stars among the detected X-ray sources, they estimate that 45-70 of the sources are cluster members. Four of the X-ray sources have previously been identified as accreting compact binaries in the cluster - three cataclysmic variables (CVs) and one quiescent neutron star. Correlating the Chandra positions with known variable stars yields 8 matches, of which 5 are probable cluster members that are likely to be binary stars with active coronae. Extrapolating these optical identifications to the remaining unidentified X-ray source population, the authors estimate that 20 - 35 of the sources are CVs and a similar number are active binaries. This likely represents most of the CVs in the cluster, but only a small fraction of all the active binaries. The authors place a 2-sigma upper limit of L<sub>x</sub> < 3 x 10<sup>30</sup> erg/s on the integrated luminosity of any additional faint, unresolved population of sources in the core of the cluster. In their paper, they explore the significance of these findings in the context of primordial versus dynamical channels for CV formation. They note that the number of CVs per unit mass in Omega Cen is at least 2 - 3 times lower than in the field, suggesting that primordial binaries that would otherwise lead to CVs are being destroyed in the cluster environment. The authors obtained 2 exposures of Omega Cen using the imaging array of the Advanced CCD Imaging Spectrometer (ACIS-I) on 2000 January 24 - 25, in "very faint" (VF) mode. The total exposure time was 72.4 ks. The authors determined source counts using 95% encircled energy radii as determined from model PSFs, derived using the CIAO tool mkpsf at an intermediate energy of ~ 1.5 keV (the PSF shape being somewhat energy dependent). Counts were extracted in three bands: "soft" (0.5 - 1.5 keV), "medium" (0.5 - 4.5 keV), and "hard" (1.5 - 6.0 keV). The authors determined the background to subtract from each source by dividing the image into 1 arcminute-wide annuli centered on the aim point in chip 3 (the innermost "annulus" being a circle of radius 1.5 arcminutes). Background values adopted for sources in a given annulus were averages determined from several source-free regions within that annulus, after verifying that the background levels were azimuthally symmetric. For 12 sources ( source_numbers 11b, 12b, 13e, 22c, 32c, 41b, 41c, 84a, 84b, 84c, 93a, and 93b) that fell in the chip gaps or near the outer edge of a chip, background regions were chosen specifically to reflect these conditions. Local background determinations were also made for a small number of sources to the west of the cluster center that lie on or near a large diffuse X-ray source ~7 arcminutes west of the cluster center (see below). Following background subtraction, the authors applied aperture corrections and also corrected for reduced effective exposure times off-axis and in the chip gaps using the exposure map. This table was created by the HEASARC in June 2011 based on the electronic versions of Table 1 from the reference paper which was obtained from the CDS (their catalog J/ApJ/697/224 file table1.dat). This is a service provided by NASA HEASARC . 2009ApJ...697..224H https://heasarc.gsfc.nasa.gov/W3Browse/all/omegcencxo.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=omegcencxo& GET text/xml 180 99999 true 201.75120833 -47.62091667 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=omegcencxo GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_omegcencxo&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public omegcencxo Omega Centauri Globular Cluster Chandra X-Ray Point Source Catal source_id Source Identification in This Catalog meta.id char nullable name IAU-Style Source Designation (CXOHDB JHHMMSS.ss+DDMMSS.s) meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable radial_distance Radial Offset from the Cluster Center in Units of Core Radii pos.angDistance double nullable hardness_ratio Hardness Ratio phot;arith.ratio;em.X-ray double nullable flux X-Ray Flux in the 0.5 - 2.5 keV Band erg/s/cm^2 phot.flux;em.X-ray double nullable sb_total_counts Soft Band Raw Source Counts (0.5-1.5keV) ct phot;em.X-ray.soft short nullable cdfs_sb_counts Corrected X-Ray Counts in Chandra Deep Field South Soft X-ray Band (0.5-2.0keV) ct phot;em.X-ray.soft double nullable alt_names Previous X-Ray Identification References meta.id char nullable optical_id Optical Identification meta.id.cross char nullable cdfs_sb_total_counts Raw X-Ray Counts in Chandra Deep Field South Soft X-ray Band (0.5-2.0keV) ct phot;em.X-ray.soft short nullable bii Galactic Latitude degree pos.galactic.lat double nullable hb_counts Hard Band Corrected Source Counts (1.5-6.0keV) ct phot;em.X-ray.medium double nullable mb_total_counts Medium Band Raw Source Counts (0.5-4.5keV) ct phot;em.X-ray short nullable mb_counts Medium Band Corrected Source Counts (0.5-4.5keV) ct phot;em.X-ray double nullable hb_total_counts Hard Band Raw Source Counts (1.5-6.0keV) ct phot;em.X-ray.medium short nullable sb_counts Soft Band Corrected Source Counts (0.5-1.5keV) ct phot;em.X-ray.soft double nullable lii Galactic Longitude degree pos.galactic.lon double nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable