Speaker
Description
Ultraluminous X-ray sources (ULXs) provide an ideal laboratory to explore super-Eddington accretion onto stellar-mass compact objects, which may be an important episode in black hole evolution. We present the evidence of super-Eddington accretion in the case of three ULX sources on the base of multi-epoch spectral and timing analysis of X-ray data taken by Chandra, XMM-Newton, Suzaku and NuSTAR satellites. Our spectral modeling reveals the inverse luminosity relation with the inner disk temperature, indicating super-Eddington accretion with emission geometrically beamed by an optically thick massive outflow. In the case of one source, we found clear spectral state transition in analogy to state transition observed in Galactic black hole binaries. Furthermore, short-timescale variability amplitude, found in this source, is correlated with spectral state, i.e. fractional variability amplitude is on the level of ~15% in hard/low state, whereas in the thermal disk-dominated high-flux state, variability drops to ~2%. Finally, we present and discuss the new detection of Fe K_{\alpha} with equivalent with of 300eV, accompanied by new detection of soft X-ray lag with amplitude of the 1300s, in case of another ULX source. This is the second ULX source where the Fe line has been detected, and the fourth, where soft X-ray lag was detected.