- Chandra X-ray Observatory observations of the globular cluster M71
- Astrophysical Journal
- Volume | Issue number
- 687 | 2
- Pages (from-to)
- Document type
- Faculty of Science (FNWI)
- Anton Pannekoek Institute for Astronomy (API)
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.
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