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A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in the Globular Cluster 47 Tucanae | | George B. Rybicki
; Craig O. Heinke
; Ramesh Narayan
; Jonathan E. Grindlay
; | | Date: |
23 Jun 2005 | | Subject: | astro-ph | | Affiliation: | CfA), Craig O. Heinke (Northwestern), Ramesh Narayan (CfA), Jonathan E. Grindlay (CfA | | Abstract: | Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate fully self-consistent hydrogen-atmosphere models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a grid of neutron star models covering a wide range of surface gravities as well as effective temperatures, which we make available to the scientific community. We present multi-epoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fit by our hydrogen-atmosphere model without any hard power-law component or narrow spectral features. If a mass of 1.4 Msol is assumed, our spectral fits require that its radius be in the range R=14.5^{+1.8}_{-1.6} km (90% confidence), larger than expected from currently preferred models of NS interiors. If its radius is assumed to be 10 km, then a mass of M=2.20^{+0.18}_{-0.16} is required. Using models with the appropriate surface gravity for each value of the mass and radius has a significant effect on the allowed parameter space. | | Source: | arXiv, astro-ph/0506563 | | Services: | Forum | Review | PDF | Favorites | |
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