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Description
The authors identify 233 X-ray sources, of which 95 are new, in a 222-ks exposure of omega Centauri with the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer detector. The limiting unabsorbed flux in the core is f<sub>X</sub>(0.5-6.0keV) ~= 3 x 10<sup>-16</sup> erg/s/cm<sup>2</sup> (L<sub>x</sub> ~= 1 x 10<sup>30</sup> erg/s at 5.2kpc). The authors estimate that ~60 +/- 20 of these are cluster members, of which ~30 lie within the core (r<sub>c</sub> = 155 arcsec), and another ~30 between 1-2 core radii. They identify four new optical counterparts, for a total of 45 likely identifications. Probable cluster members include 18 cataclysmic variables (CVs) and CV candidates, one quiescent low-mass X-ray binary, four variable stars, and five stars that are either associated with omega Cen's anomalous red giant branch or are sub-subgiants. The authors estimate that the cluster contains 40 +/- 10 CVs with L_x_> 10<sup>31</sup> erg/s, confirming that CVs are underabundant in omega Cen relative to the field. Intrinsic absorption is required to fit X-ray spectra of six of the nine brightest CVs, suggesting magnetic CVs, or high-inclination systems. Though no radio millisecond pulsars (MSPs) are currently known in omega Cen, more than 30 unidentified sources have luminosities and X-ray colors like those of MSPs found in other globular clusters; these could be responsible for the Fermi-detected gamma-ray emission from the cluster. The authors identify a CH star as the counterpart to the second brightest X-ray source in the cluster and argue that it is a symbiotic star. This is the first such giant/white dwarf binary to be identified in a globular cluster. The data were obtained over two long exposures of omega Cen using the imaging array of the Chandra X-ray Observatory's ACIS-I on 2012 April 16 and 17. The data sets have a combined exposure time of ~222ks (173.7 and 48.5ks for ObsIDs 13726 and 13727, respectively). This table was created by the HEASARC in June 2018 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/479/2834">CDS Catalog J/MNRAS/479/2834</a> file table1.dat. This is a service provided by NASA HEASARC .
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