Neutron reactions in accreting neutron stars: a new pathway to efficient crust heating

TL;DR

This paper introduces a comprehensive model for neutron star crust heating that incorporates detailed electron capture decay pathways to excited states, resulting in increased neutron emission and more continuous reaction flows with depth.

Contribution

It presents a novel calculation of electron capture decay rates to all accessible states using a deformed QRPA model, enhancing the understanding of crust heating mechanisms.

Findings

Increased neutron emission due to decay to excited states.

More continuous neutron production with depth in multi-component plasma.

Accelerated reaction flows in neutron star crusts.

Abstract

In our calculation of neutron star crust heating we include several key new model features. In earlier work electron capture (EC) only allowed neutron emission from the daughter ground-state; here we calculate, in a deformed QRPA model, EC decay rates to all states in the daughter that are allowed by Gamow-Teller selection rules and energetics. The subsequent branching ratios between the 1n,...,xn channels and the competing $\gamma$-decay are calculated in a Hauser-Feshbach model. Since EC accesses excited states, many more neutrons are emitted in our calculation than in previous work, leading to accelerated reaction flows. In our multi-component plasma model a single (EC,xn) reaction step can produce several neutron-deficient nuclei, each of which can further decay by (EC,xn). Hence, the neutron emission occurs more continuously with increasing depth as compared to that in a one-component plasma model.