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

Abstract

We perform a global 2.5D general-relativistic radiation magnetohydrodynamic simulation of supercritical accretion onto a neutron star with a 2 × 10 10 G dipolar magnetic field, as a model of a neutronstar-powered ultraluminous X-ray source (ULX). We compute a lower limit on the total luminosity of ∼ 2.5 L 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 Edd , consistent with the luminosities observed in ULXs.

High-Mass X-Ray Binaries with Be Donors as Ultraluminous X-Ray Sources

“…Some recent studies have argued that beaming is not very strong, so we assume that the effect of beaming is a factor of order unity (Takahashi & Ohsuga 2017;Erkut et al 2020;Mushtukov et al 2021) 1 . In particular, analyses based on various models suggest that beaming is weak in Swift 1 Recent numerical simulation indicates that beaming could be stronger when mag is much smaller than sph (Abarca et al 2021).…”

“…In particular, whether the magnetic field of ULX NSs is strong or weak remains hotly debated (Eksi et al 2015;Tong 2015;King & Lasota 2019;Mushtukov et al 2015Mushtukov et al , 2021Middleton et al 2019;Brightman et al 2018;Walton et al 2018). In recent years, modelw that comprehensively treat spin, magnetic field and beaming of NS ULXs have been considered (Erkut et al 2020;Mushtukov et al 2021;Abarca et al 2021).…”