Beamed emission from a neutron-star ULX in a GRRMHD simulation

TL;DR

This study uses advanced simulations to model super-critical accretion onto a neutron star, revealing highly beamed radiation that can produce apparent luminosities exceeding 100 times the Eddington limit, aligning with ULX observations.

Contribution

First 2.5D GRRMHD simulation of neutron-star accretion demonstrating beamed emission and super-Eddington luminosities in ULX models.

Findings

Luminosity exceeds 2.5 times Eddington limit

Radiation is highly beamed by disk outflows

Apparent luminosity can surpass 100 times Eddington depending on viewing angle

Abstract

We perform a global 2.5D general-relativistic radiation magnetohydrodynamic simulation of super-critical accretion onto a neutron star with a $2\times 10^{10}$ G dipolar magnetic field, as a model of a neutron-star-powered ultraluminous X-ray source (ULX). We compute a lower limit on the total luminosity of $\sim 2.5\,L_\mathrm{Edd}$, and find the radiation to be highly beamed by the accretion disk outflows. The apparent isotropic luminosity, which is a function of the viewing angle, reaches a maximum above $100\,L_\mathrm{Edd}$, consistent with the luminosities observed in ULXs.