Quiescent NIR and optical counterparts to candidate black hole X-ray binaries

TL;DR

This study presents near-infrared and optical imaging of fifteen candidate black hole X-ray binaries, detecting counterparts in quiescence for most, and explores the relationship between their luminosity differences and orbital periods.

Contribution

First comprehensive near-infrared and optical imaging of fifteen candidate black hole X-ray binaries, including new quiescent counterpart detections and analysis of luminosity trends.

Findings

Twelve counterparts detected in quiescence, with seven being first reports.

Some counterparts are fainter than previously reported.

Observed trend between luminosity difference and orbital period differs from theoretical expectations.

Abstract

We present near-infrared and optical imaging of fifteen candidate black hole X-ray binaries. In addition to quiescent observations for all sources, we also observed two of these sources (IGR J17451-3022 and XTE J1818-245) in outburst. We detect the quiescent counterpart for twelve out of fifteen sources, and for the remaining three we report limiting magnitudes. The magnitudes of the detected counterparts range between $K_s$ = 17.59 and $K_s$ = 22.29 mag. We provide (limits on) the absolute magnitudes and finding charts of all sources. Of these twelve detections in quiescence, seven represent the first quiescent reported values (for MAXI J1543-564, XTE J1726-476, IGR J17451-3022, XTE J1818-245, MAXI J1828-249, MAXI J1836-194, Swift J1910.2-0546) and two detections show fainter counterparts to XTE J1752-223 and XTE J2012+381 than previously reported. We used theoretical arguments and observed trends, for instance between the outburst and quiescent X-ray luminosity and orbital period $P_{orb}$ to derive an expected trend between $\Delta K_s$ and $P_{orb}$ of $\Delta K_s \propto \log P_{orb}^{0.565}$. Comparing this to observations we find a different behaviour. We discuss possible explanations for this result.