Exploring the spin dependence on mass inclination and distance for the newly discovered black hole X-ray binary Swift J151857.0-572147

TL;DR

This study analyzes how the spin of the black hole in Swift J151857.0-572147 depends on mass, inclination, and distance using NICER data, highlighting the importance of precise parameter measurements for accurate spin estimation.

Contribution

It introduces a continuum fitting method to explore spin dependence on key parameters for a newly discovered black hole X-ray binary.

Findings

Moderate spin (~0.7) for fiducial parameters

Spin increases with higher mass, larger distance, or lower inclination

Framework established for future precise spin measurements

Abstract

The black hole X-ray binary (BHXRB) Swift J151857.0-572147 was discovered during its first outburst in March 2024. We review the archive of NICER observations from this outburst, focusing on the soft states. We select spectra for which the disk to total flux ratio exceeds 0.8 and the coronal scattering fraction fsc is less than 25%, conditions under which the accretion disk is expected to extend to the innermost stable circular orbit (ISCO) and remains geometrically thin. Through a continuum fitting analysis, we explore the dependence of spin on mass, inclination, and distance. We constrain the spin within the parameter space typical of stellar-mass black holes (sBHs), assuming a mass around 10 solar masses, inclination angles between 20 and 60 degree, and distances between 4 and 16 kpc. For fiducial parameters: a mass of 10 solar masses, a distance of 10 kpc, and an inclination angle of 40 degree, a moderate spin of approximately 0.7 is obtained. However, precise determination of the spin will require accurate measurements of these parameters. Our analysis provides a framework to infer the spin and estimate its uncertainties once more precise measurements of mass, distance, and inclination become available. As we demonstrate, lower inclination angles, greater distances, or larger black hole masses result in higher spin values.