Non-thermal emission from AGN coronae

¹ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Dipartimento di Astronomia e Scienza dello Spazio, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: paola@arcetri.astro.it
³ Research and Scientific Support Department of ESA, ESTEC, Postbus 299, 2200, AG Noordwijk, The Netherlands

Received: 2 April 2004
Accepted: 25 February 2005

Abstract

Accretion disk coronae are believed to account for X-ray emission in Active Galactic Nuclei (AGNs). In this paper the observed emission is assumed to be due to a population of relativistic, non-thermal electrons (e.g. produced in a flare) injected at the top of an accretion disk magnetic loop. While electrons stream along magnetic field lines, their energy distribution evolves in time essentially because of inverse Compton and synchrotron losses. The corresponding time-dependent emission due, in the X-ray energy range, to the inverse Compton mechanism, has been computed. Since the typical decay time of a flare is shorter than the integration time for data acquisition in the X-ray domain, the resulting spectrum is derived as the temporal mean of the real, time-dependent emission, as originated from a series of consecutive and identical flares. The model outcome is compared to both the broad band BeppoSAX X-ray data of the bright Seyfert 1 NGC 5548 and to a few general X-ray spectral properties of Seyfert 1s as a class. The good agreement between model and observations suggests that the presently proposed non-thermal, non-stationary model could be a plausible explanation of AGN X-ray emission as an alternative to thermal coronae models.