ANDRZEJ ZDZIARSKI, N. COPERNICUS ASTRONOMICAL CENTER

PRINCETON ASTRONOMY COLLOQUIUM - MAY 4, 2004

ABSTRACT

Radiative Processes and Geometry of Accreting Black Holes

I will review spectral states of black-hole binaries and their possible unification scenarios. The hard state occurs when a hot accretion flow is present. Its dominant radiative process is thermal Comptonization. The soft states are manifestation of a cold accretion disk with a corona on its surface. The dominant radiative process in the corona is Compton scattering by hybrid, thermal-nonthermal, electrons of blackbody photons from the disk. The existence of two accretion solutions in a range of accretion rate is responsible for pronounced hysteresis in low-mass X-ray binaries, with hard-to-soft transitions taking place at Eddington ratios substantially higher than the reverse transitions.