Radiative GRMHD simulations of accretion and outflow in non-magnetized neutron stars and ultraluminous X-ray sources

We run two general relativistic radiation magnetohydrodynamic simulations of super-Eddington accretion discs around a black hole and a non-magnetized, non-rotating neutron star (NS). The NS was modelled using a reflective inner boundary condition. We observe the formation of a transition layer in the inner region of the disc in the NS simulation which leads to a larger mass outflow rate and a lower radiative luminosity over the black hole case. Sphereization of the flow leads to an observable luminosity at infinity around the Eddington value when viewed from all directions for the NS case, contrasting to the black hole case where collimation of the emission leads to observable luminosities about an order of magnitude higher when observed along the disc axis. We find the outflow to be optically thick to scattering, which would lead to the obscuring of any NS pulsations observed in corresponding ultraluminous X-ray sources.