Cassiopeia A and direct URCA cooling

Abstract

We model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A, with a microscopic nuclear equation of state featuring strong direct Urca processes and using compatible nuclear pairing gaps as well as effective masses. Several scenarios are possible to explain the features of Cas A, but only large and extended proton ${}^1{S}_0$ gaps and small neutron ${}^{3}P{F}_2$ gaps are able to accommodate also the major part of the complete current cooling data. We conclude that the possibility of strong direct Urca processes cannot be excluded from the cooling analysis.

Comments: 7 pages, 6 figures, submitted to Monthly Notices of the Royal Astronomical Society