Radiation from magnetized accretion disks in active galactic nuclei

Abstract

We present a model of active galactic nuclei (AGNs) based on accretion disks around 10^8^ M_sun_ black holes, which incorporates a strong (B ~ 10^4^ G) magnetic field in the disk, with loops above the disk in which B ~ 10^2^ G. The magnetic energy in the loops dissipates, accelerating electrons to relativistic energies. The electrons emit synchrotron and inverse-Compton radiation, much of which is reflected or scattered by gas in the disk. We calculate the emitted spectrum from infrared to gamma rays. Of the total emission, 23% goes into a v^-1^ power law and 77% into thermal radiation at 24,000 K (due to the disk, which is heated by nonthermal radiation and energetic ions). The model accounts quantitatively for the X-ray and gamma-ray backgrounds, and it accounts qualitatively for certain features observed in individual AGNs: a far- infrared cutoff, a minimum at a few microns, the ultraviolet bump, the Compton reflection bump at ~30 keV, and a gamma-ray tail.