Most Galactic black-hole binaries show semi-periodic outburst, and be classfied with different X-ray state according to the X-ray properties in the whole outburst. From onset of the outburst, the system can go through low-hard state, intermediate state or very high state, high soft state, then low hard state again (but the luminosity is only a half of the rise phase), and the last quiet state. Dur- ing the whole outburst, their X-ray properties, accretion flow and the mechanism of the X-ray radiation, show large varieties, implying the signi¯cant changes in the accretion physics. We have carried out a detailed analysis of the X-ray transient XTE J1650-500 as observed during its discovery outburst in 2001/2002 by the Rossi X-Ray Timing Explorer. By ¯tting the RXTE observations with phenomenological and physical models reasonably, we got some constrains on the Compton process for the hard state and the soft state, i.e., thermal Comptonization dominating the hard X-ray emission in the hard state and the bulk-motion Comptonization controlling in the soft state. During the state transition from the hard to the soft, a contraction of the Comptonization region (Compton cloud) with the effective surface area decreasing a factor of ~23 suggests that in addition to massaccretion rate there is another parameter responsible for the state transition in XTE J1650-500, and this second driving factor may the the scale of the Comptonizing plasma. And the anticorrelation between the flux of the Fe K-alpha emission line and the power-law flux in hard state can be well explained in the light-bending model. combing the obtained energy spectra properties with us and the prior achievement of radio observation and the timing analysis, we suggest the accretion con¯guration of the accretion flow in XTE J1650-500 is a composite of jet+corona+disk. Until now, the physical origin of the SPL (steep power-law) state generating HFQPOs, extremely high luminosity and spectra that extend to above MeV, remains one of the outstanding problems in Black-hole binaries (BHBs). Most models on the spectra of the SPL state invoke inverse Compton scattering of seed photons from the disk in a nonthermal corona. The origin of the nonthermal electrons has led to the models with complicated geometry and feedback mechanisms. Alternative models involve bulk motion Comptonization in the context of a converging sub-Keplerian flow within 50Rg of the Black Hole. Current models of the SPL state are deffcient in terms of specifying the radiation mechanisms that would imprint a given oscillation mode into the X-ray light curve. Here, we proposed a new scenario of the hard X-ray origin in the SPL state which is based on two standard processes, in which the hard X-ray photons with a power-law spectrum extending to above MeV bands is firstly produced by the synchrotron radiation of magnetized compact spots orbiting near the ISCO and then these photons are down-scattered by the thermal electrons of surrounding corona to form an observed steep spectrum. The high energy cutoff of the spectrum is only determined by the electron acceleration rate in the spot. At last, we discuss the correlations of the HFQPOs (high-frequency-quasi-periodic-oscillation) and the extreme high luminosity of the SPL state to this model.
修改评论