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



Present address: AIM, CEA/DSM - CNRS - Université Paris Diderot, Irfu/SAP, Centre de Saclay, Bat. 709, FR-91191 Gif-sur-Yvette Cedex, France.


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 to 2010 June. From Swift–Ultraviolet/Optical Telescope (UVOT) data we confirm the presence of an optical counterpart which displays variability correlated, in the soft state, to the X-ray emission observed by Swift–X-ray Telescope (XRT). The optical counterpart also displays hysteretical behaviour between the states not normally observed in the optical bands, suggesting a possible contribution from a synchrotron-emitting jet to the optical emission in the rising hard state. We offer a purely phenomenological treatment of the spectra as an indication of the canonical spectral state of the source during different periods of the outburst. We find that the high-energy hardness–intensity diagrams over two separate bands follow the canonical behaviour, confirming the spectral states. Our XRT timing analysis shows that in the hard state there is significant variability below 10 Hz which is more pronounced at low energies, while during the soft state the level of variability is consistent with being minimal. These properties of XTE J1752−223 support its candidacy as a black hole in the Galactic Centre region.