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

• Published in: Astronomy and astrophysics (Berlin) 2005-05, Vol.434 (3), p.839-848
• Main Authors: Mandal, S., Chakrabarti, S. K.
• Format: Article
• Language: English
• Subjects: accretion; accretion disks; black hole physics; hydrodynamics; radiative transfer; shock waves
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20041235

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 $\nu_{\rm bump} \sim \nu_{\rm inj} [1+\frac{4}{3}\frac{R-1} {R}\frac{1}{x_{\rm s}^{1/2}}]^{x_{\rm s}^{1/2}}$, where, $\nu_{\rm inj}$ is the frequency of the dominant photons from the pre-shock flow, and R the compression ratio of the shock located at xs. For strong shocks, a bump at a higher frequency appears predominantly due to the power-law electrons formed at the shock front.