Swift J1753.5−0127: The Black Hole Candidate with the Shortest Orbital Period

C. Zurita, M. Durant, M. A. P. Torres, T. Shahbaz, J. Casares, D. Steeghs

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 hr. 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.

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