Accretion shock signatures in the spectrum of two-temperature advective flows around black holes

Abstract

The centrifugal barrier supported boundary layer (CENBOL) of a black hole affects the spectrum exactly in the same way the boundary layer of a neutron star does. The CENBOL is caused by standing or oscillating shock waves that accelerate electrons very efficiently and produce a power-law distribution. The accelerated particles in turn emit synchrotron radiation in the presence of the magnetic field. We study the spectral properties of an accretion disk as a function of shock strength, compression ratio, flow accretion rate and flow geometry. In the absence of a satisfactory description of magnetic fields inside the advective disk, we only consider the stochastic fields and use the ratio of field energy density to gravitational energy density as a parameter. Not surprisingly, stronger fields produce larger humps due to synchrotron radiation. We not only include "conventional" synchrotron emission and Comptonization due to Maxwell-Boltzmann electrons in the gas, but also compute the effects of power-law electrons. For strong shocks, a bump is produced just above the synchrotron self-absorption frequency at Vbump ∼ v inj[l + 4/3 R-1/R 1/1/2 x8]xs1/2, where, Vinj is the frequency of the dominant photons from the pre-shock flow, and R the compression ratio of the shock located at x s. For strong shocks, a bump at a higher frequency appears predominantly due to the power-law electrons formed at the shock front. © ESO 2005.