Abstract We present a new explanation for the origin of 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 of a black hole. It has a hard spectrum that extends to above MeV energies, which is determined by the electron acceleration rate. These photons are then down-scattered by the surrounding plasma to form an observed steep spectrum. We discuss the relevance of the model to high-frequency quasi-periodic oscillations and the extremely high luminosity of the SPL state.
Keywords accretion, accretion disks — black hole physics — radiation mecha- nisms: nonthermal — X-rays: binaries
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