Signature of Accretion Shocks in Emitted Radiation From a Two Temperature Advective Flows Around Black Holes

Abstract

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 produced due to standing or oscillating shock waves and these shocks accelerate electrons very efficiently and produce a power-law distribution. The accelerated particles in turn emit synchrotron radiation in presence of the magnetic field. We study the spectral properties of an accretion disk as a function of the 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 consider the presence of only stochastic fields and use the ratio of the field energy density to the gravitational energy density to be a parameter. Not surprisingly, stronger fields produce stronger humps due to synchrotron radiation. We not only include `conventional' synchrotron emission and Comptonization due to Maxwell-Bolzmann electrons in the gas, we also compute these effects due to power-law electrons. For strong shocks, a bump is produced at a frequency just above the synchrotron self-absorption frequency at $ν_{bump} \sim ν_{inj} [1+{4/3}\frac{R-1} {R}\frac{1}{x_s^{1/2}}]^{x_s^{1/2}}$, where, $ν_{inj}$ is the frequency of the dominant photons from the pre-shock flow, $R$ is 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.

20 pages 7 figures Astronomy and Astrophysics (in press)