Dynamical Comptonization in spherical flows: black hole accretion and stellar winds Free

The transport of photons in steady, spherical, scattering flows is investigated. The moment equations are solved analytically for accretion on to a Schwarzschild black hole, taking full account of relativistic effects. We show that the emergent radiation spectrum is a power law at high frequencies with a spectral index smaller (harder spectrum) than in the non-relativistic case. Radiative transfer in an expanding envelope is also analysed. We find that adiabatic expansion produces a drift of injected monochromatic photons towards lower frequencies and the formation of a power-law, low-energy tail with spectral index − 3.