Testing exterior spacetime of the neutron star via X-ray reflection spectroscopy

TL;DR

This study investigates whether X-ray reflection spectroscopy can differentiate neutron stars from Kerr black holes by analyzing the subtle differences in their iron line profiles, especially at high spins and multipole moments.

Contribution

It demonstrates that X-ray reflection spectra can potentially distinguish neutron stars from Kerr black holes, highlighting the challenges at lower spins and multipole moments.

Findings

Small differences in iron line shapes at high spin and multipole moments.

Neutron star iron lines are hard to distinguish from Kerr black holes.

Slow rotating neutron stars are marginally consistent with Kerr black holes.

Abstract

The exterior geometry of a neutron star can be approximated by relativistic multipole moments of a parametrized metric using Ernst potential formalism. This spacetime can be tested with electromagnetic wave observation of astrophysical black holes. In the present paper, I simulate X-ray reflection spectra of a thin accretion disk with future X-ray missions. The purpose of this work is to understand whether X-ray reflection spectroscopy can distinguish the neutron star from the Kerr solution of General Relativity. I found that for the higher value of spin and multipole moment parameters, there are small differences in the shape of neutron star iron lines. It is hard to distinguish neutron star iron lines from Kerr ones due to the small deviations. Also, electromagnetic wave observation of slow rotating neutron stars is marginally consistent with Kerr black holes of general relativity.