Estimating the spin of the black hole candidate MAXI J1659-152 with the X-ray continuum-fitting method

TL;DR

This study estimates the black hole spin in MAXI J1659-152 using X-ray spectral data and the continuum-fitting method, constraining the spin to be between retrograde and moderate prograde values.

Contribution

It applies updated system parameters and the relativistic thin disk model to analyze multiple spectra, providing the first constraints on the black hole's spin in this system.

Findings

Spin constrained to -1 < a_* ≲ 0.44 at 90% confidence

Extreme retrograde spin remains a viable possibility

Inclination angle inversely correlates with spin

Abstract

As a transient X-ray binary, MAXI J1659-152 contains a black hole candidate as its compact star. MAXI J1659-152 was discovered on 2010 September 25 during its only known outburst. Previously-published studies of this outburst indicate that MAXI J1659-152 may have an extreme retrograde spin, which, if confirmed, would provide an important clue as to the origin of black hole spin. In this paper, utilizing updated dynamical binary-system parameters (i.e. the black hole mass, the orbital inclination and the source distance) provided by \cite{Torres2021}, we analyze 65 spectra of MAXI J1659-152 from \emph{RXTE}/PCA, in order to assess the spin parameter. With a final selection of 9 spectra matching our $f_{\mathrm{sc}} \lesssim 25 \%$, soft-state criteria, we apply a relativistic thin disk spectroscopic model \texttt{kerrbb2} over 3.0-45.0 keV. We find that inclination angle correlates inversely with spin, and, considering the possible values for inclination angle, we constrain spin to be $-1 < a_{*} \lesssim 0.44$ at 90\% confidence interval via X-ray continuum-fitting. We can only rule out an extreme prograde (positive) spin. We confirm that an extreme retrograde solution is possible and is not ruled out by considering accretion torques given the young age of the system.