2003/01/14 by C. O. Heinke, J. E. Grindlay, D. A. Lloyd +1 · 2 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.1086/374039
published as Astrophys.J. 588 (2003) 452-463 · 16 pages, 7 figures, accepted by ApJ
arxiv created 2003/01/14 · openalex publication_date 2003/05/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We report spectral and variability analysis of two quiescent low-mass X-ray binaries (X5 and X7, previously detected with the ROSAT HRI) in a Chandra ACIS-I observation of the globular cluster 47 Tuc. X5 demonstrates sharp eclipses with an 8.666 ± 0.01 hr period, as well as dips showing an increased N H column. The thermal spectra of X5 and X7 are well modeled by unmagnetized hydrogen atmospheres of hot neutron stars. No hard power-law component is required. A possible edge or absorption feature is identified near 0.64 keV, perhaps an O V edge from a hot wind. Spectral fits imply that X7 is significantly more massive than the canonical 1.4 M ☉ neutron star mass, with M > 1.8 M ☉ for a radius range of 9-14 km, while X5's spectrum is consistent with a neutron star of mass 1.4 M ☉ for the same radius range. Alternatively, if much of the X-ray luminosity is due to continuing accretion onto the neutron star surface, the feature may be the 0.87 keV rest-frame absorption complex (O VIII and other metal lines) intrinsic to the neutron star atmosphere, and a mass of 1.4 M ☉ for X7 may be allowed.