Disk truncation in AGN: The influence of viscosity

We use the disk-corona model (Meyer et al. 2000a) to investigate how the viscosity affects the truncation of the disk in low-luminosity AGN (LLAGN) and hard/soft spectral state transitions in AGN. Previous studies (Meyer-Hofmeister & Meyer 2001) show that the corona structure depends strongly on the value of viscosity. We attempt to do detailed calculations of the coronal structure for a series of viscous coefficients. We give an analytical fitting formula for the maximal mass evaporation rate as a function of the viscosity a. The corresponding truncation radius is also fitted as a function of the viscosity. Our results may improve the interpretation of spectral transition between soft and hard states, and the truncation radius in LLAGN.