Heating and cooling of magnetars with accreted envelopes

TL;DR

This paper models the thermal evolution of magnetars considering the effects of strong magnetic fields and different envelope compositions, revealing how these factors influence observable cooling behaviors.

Contribution

It introduces a model that incorporates magnetized envelopes and internal heat sources to better understand magnetar cooling, emphasizing the impact of magnetic fields and element composition.

Findings

Magnetized light-element envelopes simplify magnetar cooling interpretation.

Strong magnetic fields and light elements increase surface luminosity.

Massive magnetars with rapid core neutrino cooling can still exhibit high surface luminosity.

Abstract

We study the thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in an internal layer. We focus on the effect of magnetized (B > 10^{14} G) non-accreted and accreted outermost envelopes composed of different elements, from iron to hydrogen or helium. We discuss a combined effect of thermal conduction and neutrino emission in the outer neutron star crust and calculate the cooling of magnetars with a dipole magnetic field for various locations of the heat layer, heat rates and magnetic field strengths. Combined effects of strong magnetic fields and light-element composition simplify the interpretation of magnetars in our model: these effects allow one to interpret observations assuming less extreme (therefore, more realistic) heating. Massive magnetars, with fast neutrino cooling in their cores, can have higher thermal surface luminosity.