Magnetic flares and the observed optical depth in seyfert galaxies

May, 1997
6 pages
Published in:
  • Astrophys.J.Lett. 490 (1997) L13
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199720012005200920131320
Abstract: (arXiv)
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 cc, e.g., by magnetohydrodynamic waves, this pressure equilibrium can constrain the Thomson optical depth τT\tau_T to be of order unity. We suggest that this may be the reason why τT1\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 τT1\tau_T\sim 1 and that formed by many different flares spanning a range of τT\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/γ\gamma-ray spectrum of Seyfert Galaxies is produced by many independent magnetic flares with an optical depth 0.5<τT<20.5<\tau_T<2.