Long Type I X-Ray Bursts and Neutron Star Interior Physics
By A. Cumming, J. Macbeth, J. I. Zand, D. Page. 2005
143 citations recorded by the source corpus.
Two types of long-duration type I X-ray bursts have been discovered by long-term monitoring observations of accreting neutron stars: superbursts and ``intermediate duration'' bursts. We investigate the sensitivity of their ignition conditions to the interior thermal properties of the neutron star. First, we compare the observed superburst light curves to cooling models. Our fits require ignition column depths in the range (0.5-3) × 1012 g cm-2 and an energy release ≈2 × 1017 ergs g-1. The implied carbon fraction is XC > 10%, constraining models of rp-process hydrogen burning. Neutrino emission and inwards conduction of heat lead to a characteristic surface fluence of 1042 ergs, in good agreement with observations. Next, we compare ignition models to observations of superbursts. Consistent with our light-curve fits, carbon fractions XC ≳ 0.2 are needed to avoid stable burning at the lowest rates for which superbursts have been observed. Unstable carbon ignition at the observed depths requires crust temperatures ≈6 × 108 K, which implies that neutrino emission from the interior is inefficient, and the crust has a poor thermal conductivity. In particular, we cannot match observed superburst properties when Cooper pair neutrino emission from the crust is included. We conclude that an extra ingredient, for example additional heating of the accumulating fuel layer, is required to explain the observed properties of superbursts. If Cooper pair emission is less efficient than currently thought, the observed ignition depths for superbursts imply that the crust is a poor conductor, and the core neutrino emission is not more efficient than modified Urca. The observed properties of helium bursts support these conclusions, requiring inefficient crust conductivity and core neutrino emission.
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/f2a02dca04c06af19eea9caa25f38d6e2d804d84
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In Astronomy and Astrophysics
Citations in the corpus
- Thermonuclear Burst Oscillations (2012, background): “Either the system is ultracompact, so that it accretes nearly pure helium (in’t Zand et al. 2005, Cumming et al. 2006), or a thick layer of helium is built up from unstable hydrogen burning at low accretion rates (Peng, Brown & Truran 2007; Cooper & Narayan 2007a).”
- Six new candidate ultracompact X-ray binaries (2007, background): “Cumming et al. (2006), therefore, coined the term “intermediately long X-ray bursts”.”
- 2D Cooling of Magnetized Neutron Stars (2007, background): “We include the Cooper Pair Breaking and Formation emissivity (CPBF), although the eff ctivity of this process was questioned both, by observational arguments (Cumming et al. 2006) and by theoretical calculations (Leinson & Pérez 2006).”