Onset of Electron Captures and Shallow Heating in Magnetars

TL;DR

This paper investigates how magnetic field decay in magnetars can trigger electron captures in their crusts, releasing heat, with new analytical formulas valid across all magnetic field strengths and supported by nuclear data and models.

Contribution

It provides novel analytical formulas for threshold density, pressure, and heat release during electron captures in magnetar crusts, accounting for Landau-Rabi quantization effects across all magnetic regimes.

Findings

Derived accurate formulas for electron capture thresholds and heat release.

Presented numerical results based on experimental nuclear data and nuclear models.

Validated formulas across a wide range of magnetic field strengths.

Abstract

The loss of magnetic pressure accompanying the decay of the magnetic field in a magnetar may trigger exothermic electron captures by nuclei in the shallow layers of the stellar crust. Very accurate analytical formulas are obtained for the threshold density and pressure, as well as for the maximum amount of heat that can be possibly released, taking into account the Landau-Rabi quantization of electron motion. These formulas are valid for arbitrary magnetic field strengths, from the weakly quantizing regime to the most extreme situation in which electrons are all confined to the lowest level. Numerical results are also presented based on experimental nuclear data supplemented with predictions from the Brussels-Montreal model HFB-24. This same nuclear model has been already employed to calculate the equation of state in all regions of magnetars.