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Effects of the Nuclear Equation of State on Type I X-Ray Bursts: Interpretation of the X-Ray Bursts from GS 1826–24

Authors
  • 土, 肥明1, 2
  • 西村, 信哉2, 3,
  • 橋本, 正章1
  • 松尾, 康秀1
  • 野田, 常雄4
  • 長瀧, 重博2, 2
  • 1 Kyushu University, Japan , (Japan)
  • 2 RIKEN, Japan , (Japan)
  • 3 National Astronomical Observatory of Japan, Japan , (Japan)
  • 4 Kurume Institute of Technology, Japan , (Japan)
Type
Published Article
Journal
The Astrophysical Journal
Publisher
American Astronomical Society
Publication Date
Dec 10, 2021
Volume
923
Issue
1
Identifiers
DOI: 10.3847/1538-4357/ac2821
Source
ioppublishing
Disciplines
  • 330
  • High-Energy Phenomena and Fundamental Physics
License
Unknown

Abstract

Type I X-ray bursts are thermonuclear explosions on the neutron star (NS) surface caused by mass accretion from a companion star. Observations of X-ray bursts provide valuable information on X-ray binary systems, e.g., binary parameters, the chemical composition of accreted matter, and the nuclear equation of state (EOS). There have been several theoretical studies to constrain the physics of X-ray bursters. However, they have mainly focused on the burning layers above the solid crust of the NS, which brings up issues of the treatment of NS gravitational and internal energy. In this study, focusing on the microphysics inside NSs, we calculate a series of X-ray bursts using a general-relativistic stellar-evolution code with several NS EOSs. We compare the X-ray-burst models with the burst parameters of a clocked burster associated with GS 1826–24. We find a monotonic correlation between the NS radius and the light-curve profile. A larger radius shows a higher recurrence time and a large peak luminosity. In contrast, the dependence of light curves on the NS mass becomes more complicated, where neutrino cooling suppresses the efficiency of nuclear ignition. We also constrain the EOS and mass of GS 1826–24, i.e., stiffer EOSs, corresponding to larger NS radii, are not preferred due to a too-high peak luminosity. The EOS and the cooling and heating of NSs are important to discuss the theoretical and observational properties of X-ray bursts.

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