Origin of power-law X-ray emission in the Steep power-law state of X-ray Binaries

We present a new scenario of the emissive origin in the Steep Power Law (SPL) state of X-ray Binaries. The power-law component of X-ray emission is the synchrotron radiation of relativistic electrons in highly magnetized compact spots orbiting near the inner stable circular orbit (ISCO) of black hole and has a hard spectrum that extends to above MeV bands determined by electron acceleration rate. These photons are then down-scattered by the surrounding plasma and form an observed steep spectrum. The relevance of this model with high-frequency quasi-periodic oscillations (HFQPOs) and extremely high luminosity of the SPL state is discussed. Subject headings: accretion, accretion disks—black hole physics—radiation mechanisms: nonthermal—X-rays: binaries