Two-temperature Radiative Hot Accretion Flow around Neutron Stars

Abstract

Abstract Numerical simulations of radiative two-temperature hot accretion flows (HAFs) around Neutron stars (NSs) are performed. We assume that all of the energy carried by the HAF around a NS will be thermalized and radiated out at the surface of the NS. The thermal photons will propagate outwards radially and cool the HAF via Comptonization. We define as the mass accretion rate at the surface of the central object in unit of Eddington accretion rate ( , with L Edd and c being Eddington luminosity and speed of light, respectively). When is lower than ∼10−4, the cooling of the HAF is not important and outflows are very strong. When , cooling becomes important and outflows are significantly weak. In the range , the HAFs transients from a strong outflow phase to a very weak outflow phase with increase of . The properties of the HAF around a NS are also compared with those of the HAF around a BH. We find that with a similar , the dynamical properties of the HAF around a NS are quite similar as those of the HAF around a BH. However, the emitted spectrum of a HAF around a NS can be quite different from that of a HAF around a BH due to the presence of a thermal soft X-ray component coming from the surface of the NS.