Speaker
Description
We compiled the X-ray and soft gamma-ray observations of the Galactic black hole binary XTE J1859+226 in the 1999–2000 outburst from RXTE, ASCA, BeppoSAX and CGRO. Throughout systematic spectral analysis using a two-component model consisting of a multi-temperature accretion disk plus a fraction of its flux convolved with a phenomenological cutoff powerlaw component resembling Comptonizaion, we found that the innermost radius (rin) and temperature (Tin) of the disk are very variable with time in the rising phase of X-ray flux below 20 keV where several types of low-frequency quasi-periodic oscillations (QPOs) were found. After this phase, rin remains constant at around 60 km assuming a distance of 8 kpc and inclination angle of 67◦, and Tin is smoothly decayed with time. Based on these results, the constant rin is probably due to a presence of the innermost stable circular orbit (ISCO), and rin repeats moving closer and farther away from the ISCO in the rising phase. Both disk parameters are also remarkably correlated with independently analyzed timing properties such as QPO central frequency and fractional rms variability amplitude. We found that the Type-A and -B QPOs are seen only when rin is close to the ISCO, while Type-C are seen when rin is truncated and the frequency changes with a relation of rin^-1.0 . This fact supports that Type-C QPOs occurs at the inner edge of the truncated disk. For at least three of five jet ejections, we suggest that relativistic jet productions occur when rin rapidly approaches from far side to the ISCO, and disk flux, and hardness ratio also rapidly changes.
