2025ApJ...982...95K

We perform radiative magnetohydrodynamics simulations in general relativity of super-Eddington disk accretion onto neutron stars endowed with a magnetic dipole corresponding to surface strengths not exceeding 100 Giga-Gauss. Accretion is found to power strong outflows that collimate the emergent radiation of the accretion columns, leading to apparent radiative luminosities of ∼100 Eddington, when the true luminosity is a few Eddington units. Surprisingly, the collimation cone/angle widens with increasing magnetic field. Thus, in our simulations the apparent luminosity of the neutron star is substantially larger for the weaker magnetic fields (10¹⁰ G) than for the stronger ones (10¹¹ G). We conclude that a super-Eddington accreting neutron star with dipole magnetic field on the order of 10¹⁰ G is the most likely source of ultraluminous X-rays.