2006ApJ...644.1090H -
Astrophys. J., 644, 1090-1103 (2006/June-3)
A hydrogen atmosphere spectral model applied to the neutron star X7 in the globular cluster 47 Tucanae.
HEINKE C.O., RYBICKI G.B., NARAYAN R. and GRINDLAY J.E.
Abstract (from CDS):
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 new 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 self-consistent 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 multiepoch 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 fitted by our hydrogen atmosphere model without any hard power-law component or narrow spectral features. If a mass of 1.4 M☉is assumed, our spectral fits require that its radius be in the range Rns=14.5+1.8–1.6 km (90% confidence), which is larger than that expected from currently preferred models of NS interiors. If its radius is assumed to be 10 km, then a mass of Mns=2.20+0.03–0.16M☉is required. Using models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.
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Journal keyword(s):
Galaxy: Globular Clusters: Individual: NGC Number: NGC 104 - Radiative Transfer - Stars: Neutron - X-Rays: Binaries
Simbad objects:
5
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