EDP Sciences
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Volume 434, Number 3, May II 2005
Page(s) 839 - 848
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041235

A&A 434, 839-848 (2005)
DOI: 10.1051/0004-6361:20041235

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

S. Mandal1 and S. K. Chakrabarti2, 1

1  Centre for Space Physics, Chalantika 43, Garia Station Rd., Garia, Kolkata 700084, India
    e-mail: space_phys@vsnl.com
2  S.N. Bose National Centre for Basic Sciences, JD Block, Salt Lake, Sector III, Kolkata 700098, India
    e-mail: chakraba@bose.res.in

(Received 6 May 2004 / Accepted 30 December 2004)

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 $x_{\rm s}$. For strong shocks, a bump at a higher frequency appears predominantly due to the power-law electrons formed at the shock front.

Key words: black hole physics -- accretion, accretion disks -- hydrodynamics -- radiative transfer -- shock waves

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