Magnetic flares and the observed τ_t ∼ 1 in seyfert galaxies

We here consider the pressure equilibrium during an intense magnetic flare above the surface of a cold accretion disk. Under the assumption that the heating source for the plasma trapped within the flaring region is an influx of energy transported inward with a group velocity close to c, e.g., by magnetohydrodynamic waves, this pressure equilibrium can constrain the Thomson optical depth, Τ_T, to be of order unity. We suggest that this may be the reason why τ_T ∼ 1 in Seyfert galaxies. We also consider whether current data can distinguish between the spectrum produced by a single X-ray-emitting region with τ_T ∼ 1 and that formed by many different flares spanning a range of τ_T. We find that the current observations do not yet have the required energy resolution to permit such a differentiation. Thus, it is possible that the entire X-ray/γ-ray spectrum of Seyfert galaxies is produced by many independent magnetic flares with an optical depth of 0.5 < τ_T < 2.