Model of heat diffusion in the outer crust of bursting neutron stars

Abstract

ABSTRACT We study heat diffusion after an energy release in a deep spherical layer of the outer neutron star crust (107 ≲ ρ ≲ 4 × 1011 g cm−3). We demonstrate that this layer possesses specific heat-accumulating properties, absorbing heat and directing it mostly inside the star. It can absorb up to ∼1043–1044 erg due to its high heat capacity, until its temperature exceeds T ∼ 3 × 109 K and triggers a rapid neutrino cooling. A warm layer (T ∼ 108–3 × 109 K) can serve as a good heat reservoir, which is thermally decoupled from the inner crust and the stellar core for a few months. We present a toy model to explore the heat diffusion within the heat-accumulating layer, and we test this model using numerical simulations. We formulate some generic features of the heat propagation that can be useful, for instance, for the interpretation of superbursts in accreting neutron stars. We present a self-similar analysis of late afterglow after such superbursts, which can be helpful to estimate properties of bursting stars.