Improved nuclear physics near A=61 refines urca neutrino luminosities in accreted neutron star crusts

Abstract

We performed Penning trap mass measurements for $^{61}\mathrm{Zn}$ at the National Superconducting Cyclotron Laboratory and NuShellX calculations of the $^{61}\mathrm{Zn}$ and $^{62}\mathrm{Ga}$ structure using the GXPF1A Hamiltonian to obtain improved estimates of the $^{61}\mathrm{Zn}(p,\ensuremath{\gamma})^{62}\mathrm{Ga}$ and $^{60}\mathrm{Cu}(p,\ensuremath{\gamma})^{61}\mathrm{Zn}$ reaction rates. Surveying astrophysical conditions for type-I x-ray bursts with the code mesa, implementing our improved reaction rates, and taking into account updated nuclear masses for $^{61}\mathrm{V}$ and $^{61}\mathrm{Cr}$ from the recent literature, we refine the neutrino luminosity from the important mass number $A=61$ urca cooling source in accreted neutron-star crusts. This improves our understanding of the thermal barrier between deep heating in the crust and the shallow depths where extra heat is needed to explain x-ray superbursts, as well as the expected signature of crust urca neutrino emission in light curves of cooling transients.