Determining the spin of two stellar-mass black holes from disk reflection signatures

TL;DR

This study measures the spins and disk inclinations of two stellar-mass black holes using advanced reflection modeling of X-ray data, revealing high spins and disk misalignment, and reducing uncertainties related to black hole mass and distance.

Contribution

Introduces a new self-consistent reflection model that accurately estimates black hole spins and disk inclinations independently of mass and distance uncertainties.

Findings

SWIFT J1753.5-0127 has a spin of ~0.76.

GRO J1655-40 shows a significant disk misalignment.

The technique reduces uncertainties in spin measurements.

Abstract

We present measurements of the dimensionless spin parameters and inner-disk inclination of two stellar mass black holes. The spin parameter of SWIFT J1753.5-0127 and GRO J1655-40 are estimated by modelling the strong reflection signatures present in their XMM-Newton observations. Using a newly developed, self-consistent reflection model which includes the blackbody radiation of the disk as well as the effect of Comptonisation, blurred with a relativistic line function, we infer the spin parameter of SWIFT J1753.5-0127 to be 0.76 +0.11-0.15. The inclination of this system is estimated at 55+2-7 degrees. For GRO J1655-40 we find that the disk is significantly misaligned to the orbital plane, with an innermost inclination of 30+5-10 degrees. Allowing the inclination to be a free parameter we find a lower limit for the spin of 0.90, this value increases to that of a maximal rotating black hole when the inclination is set to that of the orbital plane of J1655-40. Our technique is independent of the black hole mass and distance, uncertainties in which are among the main contributors to the spin uncertainty in previous works.