A Deep Chandra Survey of the Globular Cluster 47 Tucanae: Catalog of Point Sources
Heinke, C. O.
Grindlay, J. E.
Edmonds, P. D.
Cohn, H. N.
Lugger, P. M.
Freire, P. C.
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CitationHeinke, C. O., J. E. Grindlay, P. D. Edmonds, H. N. Cohn, P. M. Lugger, F. Camilo, S. Bogdanov, and P. C. Freire. 2005. “A Deep Chandra Survey of the Globular Cluster 47 Tucanae: Catalog of Point Sources.” The Astrophysical Journal 625 (2): 796–824. https://doi.org/10.1086/429899.
AbstractWe have detected 300 X-ray sources within the half-mass radius (2.'79) of the globular cluster 47 Tucanae in a deep (281 ks) Chandra exposure. We perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variability on timescales from hours to years. Thirty-one of the new X-ray sources are identified with chromospherically active binaries from the catalogs of Albrow and coworkers. The radial distributions of detected sources imply that roughly 70 are background sources of some kind. The radial distribution of the known millisecond pulsar ( MSP) systems is consistent with that expected from mass segregation, if the average neutron star mass is 1: 39 +/- 0: 19 M(circle dot). Most source spectra are well fitted by thermal plasma models, except for quiescent low-mass X-ray binaries (qLMXBs; containing accreting neutron stars) and MSPs. We identify three new candidate qLMXBs with relatively low X-ray luminosities. One of the brightest cataclysmic variables (CVs; X10) shows evidence (a 4.7 hr period pulsation and strong soft X-ray emission) for a magnetically dominated accretion flow as in AM Her systems. Most of the bright CVs require intrinsic N(H) columns of order 10(21) cm(-2), suggesting a possible DQ Her nature. A group of X-ray sources associated with bright ( sub) giant stars also requires intrinsic absorption. By comparing the X-ray colors, luminosities, variability, and quality of spectral fits of the detected MSPs to those of unidentified sources, we estimate that a total of similar to 25 MSPs exist in 47 Tuc (< 60 at 95% confidence), regardless of their radio beaming fraction. We estimate that the total number of neutron stars in 47 Tuc is of order 300, reducing the discrepancy between theoretical neutron star retention rates and observed neutron star populations in globular clusters. Comprehensive tables of source properties and simple spectral fits are provided electronically.
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