Chandra X-ray Observatory observations of the globular cluster M71

Authors
  • R.F. Elsner
  • C.O. Heinke
  • H.N. Cohn
  • P.M. Lugger
  • J.E. Maxwell
  • I.H. Stairs
  • S.M. Ransom
  • J.W.T. Hessels
  • W. Becker
  • R.H.H. Huang
  • P.D. Edmonds
  • J.E. Grindlay
  • S. Bogdanov
  • K. Ghosh
  • M.C. Weisskopf
Publication date 2008
Journal Astrophysical Journal
Volume | Issue number 687 | 2
Pages (from-to) 1019-1034
Organisations
  • Faculty of Science (FNWI) - Anton Pannekoek Institute for Astronomy (API)
Abstract
We observe the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-Ray Observatory to study its faint X-ray populations. Five X-ray sources are found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2 hr. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources are found within the half-mass radius, reaching to a limiting luminosity of 1.5 x 10(30) ergs s (1) (0.3-8 keV). From a radial distribution analysis, we find that 18 +/- 6 of these 29 sources are associated with M71, somewhat more than predicted, and that 11 +/- 6 are background sources, both Galactic and extragalactic. M71 appears to have more X-ray sources in the range L-X - 10(30) -10(31) ergs s(-1) than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources and describe the results of ground-based optical counterpart searches.
Document type Article
Published at https://doi.org/10.1086/591899
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