2016/09/22 by Alex Deibel, Andrew Cumming, Edward F. Brown +1
Physics and Astronomy · #Accretion (finance) #Astrophysical Phenomena and Observations #Cooling curve #Crust #Gamma-ray bursts and supernovae #Inner core #Neutron #Neutron star #Pulsars and Gravitational Waves Research #Thermal #Thermal equilibrium #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aa6a19
9 pages, 5 Figures. Submitted to ApJ
arxiv created 2016/09/22 · openalex created_date 2016/10/07 · openalex publication_date 2017/04/20 · arxiv updated 2017/04/26 · openalex updated_date 2026/08/06
Abstract An accretion outburst onto a neutron star transient heats the neutron star’s crust out of thermal equilibrium with the core. After the outburst, the crust thermally relaxes toward equilibrium with the neutron star core, and the surface thermal emission powers the quiescent X-ray light curve. Crust cooling models predict that thermal equilibrium of the crust will be established into quiescence. Recent observations of the cooling neutron star transient MXB 1659-29, however, suggest that the crust did not reach thermal equilibrium with the core on the predicted timescale and continued to cool after into quiescence. Because the quiescent light curve reveals successively deeper layers of the crust, the observed late-time cooling of MXB 1659-29 depends on the thermal transport in the inner crust. In particular, the observed late-time cooling is consistent with a low thermal conductivity layer near the depth predicted for nuclear pasta that maintains a temperature gradient between the neutron star’s inner crust and core for thousands of days into quiescence. As a result, the temperature near the crust–core boundary remains above the critical temperature for neutron superfluidity, and a layer of normal neutrons forms in the inner crust. We find that the late-time cooling of MXB 1659-29 is consistent with heat release from a normal neutron layer near the crust–core boundary with a long thermal time. We also investigate the effect of inner crust physics on the predicted cooling curves of the accreting transient KS 1731-260 and the magnetar SGR 1627-41.