Work

Energy Flow and Radiation Efficiency in Radiative GRMHD Simulations of Neutron Star Ultraluminous X-Ray Sources

Year: 2025

Type: article

Abstract: We investigate numerically the energy flow and radiation efficiency of accreting neutron stars as potential ultraluminous X-ray sources (ULXs). We perform 10 simulations in radiative general relativistic magnetohydrodynamics, exploring six different magnetic dipole strengths ranging from 10 to 100 GigaGauss, along with three accretion rates, 100, 300, and 1000 Eddington luminosity units. Our results show that the energy efficiency in simulations with a strong magnetic dipole of 100 GigaGauss is approximately half that of simulations with a magnetic dipole an order of magnitude weaker. Consequently, radiation efficiency is lower in simulations with stronger magnetic dipoles. We also demonstrate that outflow power increases as the magnetic dipole weakens, resulting in stronger beaming in simulations with weaker magnetic dipoles. As a result of beaming, simulations with magnetic dipole strengths below 30 GigaGauss exhibit apparent luminosities consistent with those observed in ULXs. As for the accretion rates, we find that higher accretion rates lead to more powerful outflows, higher kinetic efficiency, and lower radiation efficiency compared to those of lower accretion rate simulations.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/ae11af

Authors: Fatemeh Kayanikhoo, Włodek Kluźniak, David Abarca, Miljenko Čemeljić

Institutions: Silesian University in Opava, Nicolaus Copernicus Astronomical Center

Language: English

Topic: Astrophysical Phenomena and Observations

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499

Funders: Grantová Agentura České Republiky, Narodowe Centrum Nauki, Infrastruktura PL-Grid, Academic Computer Centre Cyfronet, AGH University of Science and Technology