Physics
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008acasn..49..243n&link_type=abstract
Acta Astronomica Sinica, vol. 49, no. 3, p. 243-250
Physics
Physical Data And Process: Black Hole Physics, Accretion: Accretion Disks, X-Rays: Binaries
Scientific paper
The disk corona evaporation model (Meyer et al. 2000; Liu et al. 2002) has been established to explain the spectral state transition and disk truncation in black hole X-ray transients and supermassive black holes. Simply estimation (Meyer et al. 2000) and numerical calculation (Meyer et al. 2001) show that the transition luminosity is strongly dependent on the viscous parameter ?, so is the truncation radius at low/hard state of accreting black holes. This paper studies study in detail the influence of viscous parameter on the maximal evaporation rate and the corresponding radius, and hence the influence on the spectral state transition and disk truncation. On the basis of numerical calculations for a number of viscous parameter values, It is show how the transition rate and truncation radius analytically vary with viscous parameter ? by fitting the numerical data. In section 2, a simple description of disk corona model (Meyer et al. 2000) is given. In section 3 the detailed numerical results are present. Assuming a typical AGN black hole of 108 solar mass, the calculate coronal structure for a series of viscous coefficients is calculated the numerical data into analytical forms for the relation between the maximal mass evaporation rate and viscosity ?, M/?MEDD ? 1.08±3.35 , and for the relation between the truncation radius and the viscosity, R/Rs ? 36.11±1.94 . The results are also shown in Figs.2a and 2b. These results demonstrate that the viscosity of the corona gas strongly affects the truncation radius of an accretion disk and the spectral transition. For comparison, The results for a 10 solar mass black hole are given. The influence of viscosity on the evaporation rate and disk truncation are the same as that for supermassive black holes. This confirms previous work that the evaporation rate (in Eddington accretion rate) and the truncation radius(in Schwarzschild radius unit) are independent on the mass of the central black hole. In Section 4 our theoretical results to are applied some X-ray transients and AGN. Assuming the viscous parameter is a free parameter, we could fit some of the observations and explain the spectral transitions between soft states and hard states, and the variation of truncation radius for a few black hole binaries such as XTE J1118+480, GX 339-4, and AGN, NGC 4636.
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