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arXiv · astro-ph/0306619

Optical Counterparts of X-Ray Point Sources Observed by CHANDRA in NGC5128: 20 New Globular Cluster X-Ray Sources

Dante Minniti·Marina Rejkuba·Jose G. Funes S. J.·Sanae Akiyama
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Abstract

VLT images in $BVI$ are used to identify the optical counterparts to bright CHANDRA X-ray points sources discovered by Kraft et al. (2001, ApJ, 560, 675) in NGC5128. Of a total of 111 X-ray point sources with L_X>2*10^{36} ergs/s present in a 56 arcmin^2 field centered on this galaxy, 58 have optical counterparts. Based on the sizes, optical magnitudes and colors, 20 new globular cluster counterparts of X-ray sources are identified, plus 3 identified based on their sizes. This brings the total number of globular cluster X-ray sources in this galaxy to 33, and establishes that 30% of the X-ray point sources in NGC5128 are associated with globular clusters. These X-ray globular clusters occupy the brightest end of the globular cluster luminosity function, indicating that bright low-mass X-ray binaries are preferentially found in massive clusters. Most of the globular clusters with X-ray sources have red colors, with 1.0 10^{37} erg/sec. There is, however, no globular cluster X-ray source in NGC5128 as bright as expected for an accreting black hole. In addition, 31 optical counterparts of X-ray point sources that are not associated with globular clusters are identified. Finally, 53 X-ray point sources (48% of the population), do not have any optical counterparts down to the faintest magnitude limits (B=25).

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Dante Minniti, Marina Rejkuba, Jose G. Funes S. J., Sanae Akiyama. 2003-09-12. Optical Counterparts of X-Ray Point Sources Observed by CHANDRA in NGC5128: 20 New Globular Cluster X-Ray Sources. https://doi.org/10.1086/379642

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