On Nonthermal Models for Active Galactic Nuclei

In the nonthermal model for radio-quiet AGN proposed by Band and Grindlay (1986), the flat hard X-ray power-law spectrum results from the scattering of a luminous UV source (observed as the 'big blue bump') by the relativistic electrons that also produce the IR and soft X-ray continuum by synchrotron emission. In the current work the quantitative model is shown to be relatively insensitive to more complicated, realistic geometries. The absorption of gamma rays due to pair creation can explain the break seen or inferred at about 3 MeV in the spectra of both individual AGN and the gamma-ray background. However, the explanation of the apparent universality of the L(nu) proportional to nu exp -0.7 spectrum in AGNs in terms of pair creation fails when applied to detailed source models, and the underlying spectral shape remains intrinsic to the poorly understood electron acceleration mechanism. The model's parameters are consistent with a nonthermal source 10 Schwarzschild radii around a massive black hole, with a magnetic field in approximate equipartition with the photon flux from the accretion disk.