2005/06/30 by Craig O. Heinke, C. O. Heinke, G. B. Rybicki +4 · 14 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics #Atmosphere (unit) #Computational physics #Gamma-ray bursts and supernovae #Globular cluster #Neutron star #Opacity #Optics #Physics #Pulsars and Gravitational Waves Research #RADIUS #Stars #astro-ph
paper · pdf · doi:10.1086/503701
published as Astrophys.J.644:1090-1103,2006 · 14 pages, 6 figures, ApJ in press (replaced with accepted version)
arxiv created 2006/03/01 · openalex publication_date 2006/06/19 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 R ns = 14.5 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 M ns = 2.20 M ☉ 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.