A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in the Globular Cluster 47 Tucanae

By C. Heinke, G. Rybicki, Ramesh Narayan, J. Grindlay. 2005

263 citations recorded by the source corpus.

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 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 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.

Subfields: Astronomy and Astrophysics

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In Astronomy and Astrophysics

1. J. Lattimer
2. A. Steiner
3. F. Özel
4. S. Guillot
5. T. Güver
6. C. Heinke
7. Dimitrios Psaltis
8. E. Brown

Citations in the corpus

• THE MASS AND RADIUS OF THE NEUTRON STAR IN EXO 1745−248 (2008, background): “…from globular cluster neutron stars in binaries emitting thermally during quiescence, such as X7 in 47 Tuc and others in ω Cen, M 13, and NGC 2808 (Heinke et al. 2006; Webb & Barret 2007; note that we do not consider here isolated neutron stars such as RX J1856–3754 because of the unquantified…”
• THE EQUATION OF STATE FROM OBSERVED MASSES AND RADII OF NEUTRON STARS (2010, background): “Some of the strongest constraints on properties of transient n utron stars are for X7 in the globular cluster 47 Tuc (Heinke et al. 2006), and for the neutron stars in the globular clustersω Cen and M13 (Webb & Barret 2007).”
• CONSTRAINING THE SYMMETRY PARAMETERS OF THE NUCLEAR INTERACTION (2012, background): “Nowquiescent neutron stars in formerly accreting binaries in globular clusters (Heinke et al. 2006; Webb & Barret 2007; Guillot et al. 2011) are promising because it is believed that recent accretion has both suppressed the surface magnetic fields and rendered their atmospheres with a nearly pure…”
• THE DENSE MATTER EQUATION OF STATE FROM NEUTRON STAR RADIUS AND MASS MEASUREMENTS (2015, background): “Observations of similar neutron stars during quiescence have yielded measurements of their apparent angular sizes, which leads to a determination of the radii with correlated uncertainties with the neutron star mass (Heinke et al. 2006, 2014; Webb & Barret 2007; Guillot et al. 2011, 2013).”
• THE DISTANCE, MASS, AND RADIUS OF THE NEUTRON STAR IN 4U 1608−52 (2008, background): “Such measurements have been carried out on globular cluster neutron stars in binaries emitting thermally during quiescence, such as X7 in 47 Tuc and others in ω Cen, M13, and NGC 2808 (Heinke et al. 2006; Webb & Barret 2007).”
• MEASUREMENT OF THE RADIUS OF NEUTRON STARS WITH HIGH SIGNAL-TO-NOISE QUIESCENT LOW-MASS X-RAY BINARIES IN GLOBULAR CLUSTERS (2012, methodology): “The qLMXB 47Tuc X7 has a reported radius RNS = 14.5 +1.6 −1.4 km for MNS = 1.4M⊙ (Heinke et al. 2006), supporting stiff dEoSs, such as MS0/2 (Müller & Serot 1996).”
• NEUTRON STAR MASSES AND RADII FROM QUIESCENT LOW-MASS X-RAY BINARIES (2013, methodology): “Pure H atmosphere models (Rajagopal & Romani 2006; Zavlin, Pavlov & Shibanov 1996; McClintock, Narayan & Rybicki 2004; Heinke et al. 2006; Haakonsen et al. 2012) applied to QLMXBs predict neutron star radii compatible with theoretical radius estimates, compared, for example, to blackbody models…”
• Constraining the mass and radius of neutron stars in globular clusters (2017, methodology): “Deep observations of the relatively bright (few 1033 erg/s) quiescent LMXB X7 in 47 Tuc gave apparently tight constraints and a large inferred radius (Heinke et al. 2006a), but suffered significantly from an instrumental systematic uncertainty, pileup.”
• THE MASS AND RADIUS OF THE NEUTRON STAR IN 4U 1820−30 (2010, unknown): “The mass and radius reported here are also consistent with the broad constraints ob- tained on neutron star properties by observations of other low-mass X-ray binaries in quiescence (Rutledge et al. 2002; Heinke et al. 2006; Webb & Barret 2007).”