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 inwards with a group velocity close to c , e.g. , by magnetohydrodynamic waves , this pressure equilibrium can constrain the Thomson optical depth \tau _ { T } to be of order unity .
We suggest that this may be the reason why \tau _ { T } \sim 1 in Seyfert Galaxies .
We also consider whether current data can distinguish between the spectrum produced by a single X-ray emitting region with \tau _ { T } \sim 1 and that formed by many different flares spanning a range of \tau _ { 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/ \gamma -ray spectrum of Seyfert Galaxies is produced by many independent magnetic flares with an optical depth 0.5 < \tau _ { T } < 2 .