Nuclear and Particle Physics, Astrophysics and Cosmology, T-2

Nuclear reactions in the accreting Neutron Star Crust: a bridge of understanding between surface burning and core cooling

Sanjib Gupta
T-16, LANL

The thermal structure of the crust of an accreting neutron star is determined by deep crustal heating reaction rates, crust conductivity and crust neutrino cooling. Each of these is directly related tccreted from the companion star, which first undergoes surface burning by the rp-process and then a series of Electron Captures(EC) as the rising electron chemical potential drives EC on increasingly neutron-rich nuclei. We show for the first time in a full reaction network the effects of an additional driving force - the neutron chemical potential which determines the balance between (1) removal of neutrons by EC to highly excited states above several neutron separation energies and (2) addition of neutrons by (n,gamma) radiative capture reactions. The combination of driving forces results in a highly non-equilibrium nucleosynthesis pathway that is directed in the opposite direction from thpurely density-driven. The efficiency of this non-thermal process brings into question the role of fon Star, particularly at the crust-core boundary. esting property of expanding even a single-species initial network into a heterogeneous multi-component plasma in which the memory of the initial compplications for the crust thermal profile for a wide range of neutron stars which can lead to tighter constraints on core cooling and also for the crustal ignition of carbon leading to X-ray superbursts.

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