Investigating Urca Cooling in Neutron Star Crusts

Wei Jia Ong

Lawrence Livermore National Laboratory

Observations of quasi-persistent X-ray transients, neutron stars which exhibit alternate phases of accretion and cooling, yield information about the interior structure of a neutron star. During quiescence, the X-ray profile and luminosity depend on the thermal evolution and structure of the neutron star. The electron degeneracy in the crust allows electron captures to occur on the rp-process ashes, transforming them into increasingly neutron-rich species as the depth of the ash increases. At the boundaries between species, Urca cycling can occur, leading to intense neutrino cooling. The strength of this cooling depends significantly on the b decay transition strength between ground states of these neutron-rich nuclei. A recent experimental effort to precisely quantify the ground state to ground state transition strength of the potentially strong cooler 61V will be presented, along with prospects for further experimental work.