Thomas J. Maccarone

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

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.

Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704

We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597-3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation implying an orbital period of ~46 minutes and a projected semi-major axis of ~5 lt-ms, which makes IGR J16597-3704 an ultra-compact X-ray binary system. We estimated a minimum companion mass of 0.0065 solar masses, assuming a neutron star mass of 1.4 solar masses, and an inclination angle of <75 degrees (suggested by the absence of eclipses or dips in its light-curve). The broad-band energy spectrum of the source is well described by a disk blackbody component (kT ~1.4 keV) plus a comptonised power-law with photon index ~2.3 and an electron temperature of ~30 keV. Radio pulsations from the source were searched for with the Parkes observatory and not detected.

Swift observations of black hole candidate XTE J1752-223 during outburst

Here we summarise the Swift broadband observations of the recently discovered X-ray transient and black hole candidate, XTE J1752-223,obtained over the period of outburst from October 2009 to June 2010. We offer a 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. 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. 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.