Black hole candidate XTE J1752-223: Swift observations of canonical states during outburst

Abstract

We present Swift broad-band observations of the recently discovered black hole candidate,X-ray transient, XTE J1752-223, obtained over the period of outburst from 2009 October to2010 June. From Swift–Ultraviolet/Optical Telescope (UVOT) data we confirm the presenceof an optical counterpart which displays variability correlated, in the soft state, to the X-rayemission observed by Swift–X-ray Telescope (XRT). The optical counterpart also displayshysteretical behaviour between the states not normally observed in the optical bands, suggestinga possible contribution from a synchrotron-emitting jet to the optical emission in the risinghard state. We offer a purely phenomenological treatment of the spectra as an indication ofthe canonical spectral state of the source during different periods of the outburst. We find thatthe high-energy hardness–intensity diagrams over two separate bands follow the canonicalbehaviour, confirming the spectral states. Our XRT timing analysis shows that in the hard statethere is significant variability below 10 Hz which is more pronounced at low energies, whileduring the soft state the level of variability is consistent with being minimal. These propertiesof XTE J1752-223 support its candidacy as a black hole in the Galactic Centre region