Beamed super-Eddington emissionfrom a weakly magnetized neutron star- an ultraluminous X-ray source (ULX)

Abstract:

We model an ultraluminous X-ray source using a global 2D axisymmetric general relativistic radiation magnetohydrodynamic simulation of super-Eddington accretion onto a neutron star with a 10 billion Gauss dipolar magnetic field. We found that the magnetic confinement of the gas into accretion columns along with the interaction of the gas with the neutron star surface produce a total luminosity of a few times the Eddington limit. Furthermore, this radiation is beamed by outflows from the accretion disk causing the apparent isotropic luminosity to exceed $10^{40}$ erg s$^{-1}$, showing that low-magnetic field neutron stars can be good candidates for the central engines of ULXs.