Diffusive nuclear burning in cooling simulations and application to new temperature data of the Cassiopeia A neutron star

Abstract

A critical relation in the study of neutron star cooling is the one between surface temperature and interior temperature. This relation is determined by the composition of the neutron star envelope and can be affected by the process of diffusive nuclear burning (DNB), which occurs when elements diffuse to depths where the density and temperature are sufficiently high to ignite nuclear burning. We calculate models of H-He and He-C envelopes that include DNB and obtain analytic temperature relations that can be used in neutron star cooling simulations. We find that DNB can lead to a rapidly changing envelope composition and prevents the build-up of thermally stable hydrogen columns y${}_H$ > 10${}^7$ g cm${}^{-2}$, while DNB can make helium envelopes more transparent to heat flux for surface temperatures $T_s$ > 2 $\times 10^6$ K. We perform neutron star cooling simulations in which we evolve temperature and envelope composition, with the latter due to DNB and accretion from the interstellar medium. We find that a time-dependent envelope composition can be relevant for understanding the long-term cooling behaviour of isolated neutron stars. We also report on the latest Chandra observations of the young neutron star in the Cassiopeia A supernova remnant; the resulting 13 temperature measurements over more than 18 years yield a ten-year cooling rate of $\approx$ 2%. Finally, we fit the observed cooling trend of the Cassiopeia A neutron star with a model that includes DNB in the envelope.

16 pages, 15 figures, 4 tables; accepted for publication in MNRAS

References in corpus (12)

• The NumPy array: a structure for efficient numerical computation
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant
• Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star
• Cooling rates of neutron stars and the young neutron star in the Cassiopeia A supernova remnant
• Central Compact Objects in Supernova Remnants
• Cooling of Accretion-Heated Neutron Stars
• Nucleon effective masses within the Brueckner-Hartree-Fock theory: Impact on stellar neutrino emission
• Axion mass limit from observations of the neutron star in Cassiopeia A
• Modeling the X-rays from the Central Compact Object PSR J1852+0040 in Kesteven 79: Evidence for a Strongly Magnetized Neutron Star
• Study of a new central compact object: The neutron star in the supernova remnant G15.9+0.2
• Opacities and spectra of hydrogen atmospheres of moderately magnetized neutron stars

Cited by in corpus (6)

• Thermal luminosities of cooling neutron stars
• Magnetic, thermal and rotational evolution of isolated neutron stars
• NS 1987A in SN 1987A
• Force on a neutron quantised vortex pinned to proton fluxoids in the superfluid core of cold neutron stars
• Crust cooling of the neutron star in Aql X-1: Different depth and magnitude of shallow heating during similar accretion outbursts
• Cooling of the Cassiopeia A neutron star and the effect of diffusive nuclear burning