The optical counterpart of the bright x-ray transient swift j1745-26
/ Authors
T. Muñoz-Darias, A. D. U. Postigo, A. D. U. Postigo, D. M. Russell, D. M. Russell, S. Guziy, J. Gorosabel, J. Gorosabel, J. Gorosabel, J. Casares
and 12 more authors
J. Casares, M. Armas Padilla, P. Charles, P. Charles, R. Fender, T. Belloni, F. Lewis, S. Motta, A. Castro-Tirado, C. Mundell, R. S'anchez-Ram'irez, C. Thöne
/ Abstract
We present a 30-day monitoring campaign of the optical counterpart of the bright X-ray transient Swift J1745−26, starting only 19 min after the discovery of the source. We observe the system peaking at i′ ∼ 17.6 on day six (MJD 561 92) to then decay at a rate of ∼0.04 mag d−1. We show that the optical peak occurs at least 3 d later than the hard X-ray (15-50 keV) flux peak. Our measurements result in an outburst amplitude greater than 4.3 mag, which favours an orbital period ≲21 h and a companion star with a spectral type later than ∼A0. Spectroscopic observations taken with the Gran Telescopio de Canarias 10.4 m telescope reveal a broad (full width at half-maximum ∼1100 km s−1), double-peaked Hα emission line from which we constrain the radial velocity semi-amplitude of the donor to be K2 > 250 km s−1. The breadth of the line and the observed optical and X-ray fluxes suggest that Swift J1745−26 is a new black hole candidate located closer than ∼7 kpc.
Journal: Monthly Notices of the Royal Astronomical Society
DOI: 10.1093/mnras/stt532