Models of crustal heating in accreting neutron stars^*

N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland e-mail: [haensel;jlz]@camk.edu.pl

Received: 30 August 2007
Accepted: 8 November 2007

Abstract

Aims.We calculate heating associated with non-equilibrium nuclear reactions in accreting neutron-star crusts, taking into account the suppression of neutrino losses demonstrated recently by Gupta et al. We consider two initial compositions of the nuclear-burning ashes, A_i = 56 and A_i = 106. We study the dependence of the integrated crustal heating on uncertainties plaguing pycnonuclear reaction models.

Methods.We use one-component plasma approximation, with compressible liquid-drop model of Mackie and Baym to describe nuclei. We follow the evolution of a crust shell from 10⁸ g cm^-3 to 10^13.6 g cm^-3.

Results.The integrated heating in the outer crust agrees nicely with results of self-consistent multicomponent plasma simulations: earlier results fall between our curves obtained for A_i = 56 and A_i = 106. The total crustal heat per one accreted nucleon ranges between 1.5 MeV/nucleon to 1.9 MeV/nucleon for A_i = 106 and A_i = 56, respectively. The value of Q_tot weakly depends on the presence of pycnonuclear reactions at 10¹²-10¹³ g cm^-3. The remarkable insensitivity of Q_tot to the distribution of nuclear processes in accreted crust is explained.