The beaming pattern and spectrum of radiation from inverse Compton scattering in blazars

By including Klein-Nishina effects, we generalize previous calculations of the beaming pattern of photons produced by inverse Compton scattering. For an isotropic distribution of soft photons upscattered by nonthermal electro ns with a power-law density distribution n(gamma) proportional to gamma (-p ), embedded in a plasma moving with relativistic bulk speed, we show that t he observed radiation intensity is proportional to D+p, where D is the Dopp ler boosting factor. This agrees with previous computations performed in th e Thomson limit, where the observed spectral index is alpha = (p - 1)/2 and the beaming pattern is D4+2 alpha. Independent of D, Klein-Nishina effects limit the location of the peak energy of the observed spectral energy dist ribution such that epsilon (peak) less than or similar to 1/epsilon (0), wh ere epsilon (0) is the energy of the seed photons in units of m(e)c(2). Ass uming that the seed photons originate in the broad-line region, we demonstr ate that the GeV emission of blazars is significantly modified by Klein-Nis hina effects, the spectrum being softer than that calculated in the Thomson limit. We further show that the change in the spectral index of the invers e Compton emission across epsilon (peak) can exceed the value of 0.5 predic ted by computations performed in the Thomson limit. The model spectra agree with OSSE and COMPTEL limits on this break without invoking the effects of differential absorption at the edge of a gamma-ray photosphere.