Quiescent X-Ray/Optical Counterparts of the Black Hole Transient H 1705-250

TL;DR

This study reports a new Chandra X-ray observation of the black hole transient H 1705-250 in quiescence, detecting it barely and estimating its luminosity, while also analyzing optical variability over several years.

Contribution

First detection of H 1705-250 in quiescence with Chandra, providing refined position and long-term optical variability analysis.

Findings

Quiescent X-ray luminosity estimated at ~9.1e30 erg/s.

Detected optical variability in the quiescent state.

Refined the source position using optical imaging.

Abstract

We report the result of a new Chandra observation of the black hole X-ray transient H 1705-250 in quiescence. H 1705-250 was barely detected in the new 50 ks Chandra observation. With 5 detected counts, we estimate the source quiescent luminosity to be Lx~9.1e30 erg/s in the 0.5-10 keV band (adopting a distance of 8.6 kpc). This value is in line with the quiescent luminosities found among other black hole X-ray binaries with similar orbital periods. By using images taken with the Faulkes Telescope North, we derive a refined position of H 1705-250. We also present the long-term lightcurve of the optical counterpart from 2006 to 2012, and show evidence for variability in quiescence.