The observed thermal relaxation of transiently accreting neutron stars during quiescence periods in low-mass x-ray binaries suggests the existence of unknown heat sources in the shallow layers of neutron-star crust. Making use of existing experimental nuclear data, we estimate the maximum possible amount of heat that can be deposited in the outer crust of an accreting neutron star due to electron captures and pycnonuclear fusion reactions triggered by the burial of x-ray burst ashes.

• Received 16 April 2020
• Accepted 1 July 2020

DOI:https://doi.org/10.1103/PhysRevC.102.015804