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

TL;DR

This paper reports Swift observations of the black hole candidate XTE J1752-223 during outburst, analyzing its spectral states, optical variability, and timing properties to confirm its black hole nature.

Contribution

It provides detailed broadband spectral and timing analysis of XTE J1752-223, highlighting optical variability and state-dependent behaviors during outburst.

Findings

Optical counterpart shows correlated variability with X-ray emission in the soft state.

Hysteretical optical behavior suggests jet contribution in the rising hard state.

Spectral state analysis confirms canonical behavior through hardness-intensity diagrams.

Abstract

We present Swift broadband observations of the recently discovered black hole candidate, X-ray transient, XTE J1752-223, obtained over the period of outburst from October 2009 to June 2010. From Swift-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-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 follows the canonical behavior, confirming the spectral states. Our XRT timing analysis shows that in the hard state there is significant variability below 10Hz 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.