Revisiting the fundamental parameters for the black hole X-ray transient Swift J1753.5-0127

TL;DR

This study uses optical spectroscopy and photometry to analyze the black hole X-ray transient Swift J1753.5-0127 in quiescence, deriving its binary parameters, companion star type, and distance, revealing a high black hole mass and significant natal kick.

Contribution

First detailed optical spectroscopic and photometric analysis of Swift J1753.5-0127 in quiescence, estimating key binary parameters and black hole mass using empirical correlations.

Findings

Black hole mass estimated at 8.8 solar masses.

Orbital period measured at approximately 3.26 hours.

Distance to the source is about 3.9 kpc.

Abstract

We present time-resolved Gran Telescopio Canarias optical spectroscopy and William Herschel Telescope $i$-band photometry of the X-ray transient SWIFT J1753.5-0127 in quiescence. The $i$-band light curve is dominated by flickering with an amplitude of $\sim 0.5$ mag and shows no evidence of the ellipsoidal modulation of the companion star. The telluric-corrected average spectrum, on the other hand, reveals the presence of weak (strongly veiled) TiO bands at $7055$ \.A and $7589$ \.A. We used them for a spectral classification, finding an M4-5 V companion star. However, as velocity shifts are not clearly detected in the individual spectra, we turned the analysis to the double-peaked H$\alpha$ emission line from the accretion disc. By exploiting the empirical correlations established for quiescent X-ray transients between the line morphology and fundamental binary parameters, we estimated the radial velocity semi-amplitude of the companion $K_2 = 820 \pm 36$ km s$^{-1}$, a mass ratio $q = 0.023 \pm 0.006$ and an inclination $i = 79 \pm 5$ deg. Moreover, an orbital period of $3.26 \pm 0.02$ h was measured from the modulation of the centroid velocities and the double-peak trough depth of the H$\alpha$ profile. These quantities yielded a mass function $f(M_1) = 7.8 \pm 1.0$ M$_\odot$ and black hole and companion star masses of $M_1 = 8.8 \pm 1.3$ M$_\odot$ and $M_2 = 0.20 \pm 0.06$ M$_\odot$, respectively. The companion star mass is in line with the spectral classification obtained from the relative depth of the TiO bands. Based on the mean quiescent magnitude ($i = 21.4 \pm 0.1$), orbital period, and interstellar extinction, we estimate the distance to the source to be $3.9 \pm 0.7$ kpc and a Galactic plane elevation of $0.8 \pm 0.2$ kpc, supporting the case for a large natal kick.