Swift J1753.5-0127: The Black Hole Candidate with the shortest orbital period

TL;DR

This study presents detailed optical observations of Swift J1753.5-0127, revealing it has the shortest known orbital period among black hole candidates, with complex light curve behavior and a likely superhump period.

Contribution

It provides the first precise measurement of the orbital period of Swift J1753.5-0127, establishing it as the black hole candidate with the shortest orbital period.

Findings

Orbital period of 3.2443 hours identified.

Light curves show complex, non-sinusoidal variability.

Distance estimates suggest a location in the Galactic halo.

Abstract

We present time-resolved photometry of the optical counterpart to the black hole candidate Swift J1753.5-0127, which has remained in the low/hard X-ray state and bright at optical/IR wavelengths since its discovery in 2005. At the time of our observations Swift J1753.5-0127 does not show a decay trend but remains stable at R=16.45 with a night to night variability of ~0.05 mag. The R-band light curves, taken from 2007 June 3 to August 31, are not sinusoidal, but exhibit a complex morphology with remarkable changes in shape and amplitude. The best period determination is 3.2443+-0.0010 hours. This photometric period is likely a superhump period, slightly larger than the orbital period. Therefore, Swift J1753.5-0127 is the black hole candidate with the shortest orbital period observed to date. Our estimation of the distance is comparable to values previously published and likely places Swift J1753.5-0127 in the Galactic halo.