Onset of Electron Captures and Shallow Heating in Magnetars

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.

Internal Heating in Magnetars: Role of Electron Captures

“…Although for simplicity we have considered an extremely quantizing magnetic field, we have shown that the maximum amount of heat is essentially determined by nuclear data alone. Therefore, our estimate remains a fairly good approximation for neutron stars with lower magnetic fields, as confirmed by our recent study [27]. Only the location of the heat sources will vary substantially depending on the magnetic field strength.…”