ON THE BEAMING STATISTICS OF GAMMA-RAY SOURCES

The beaming pattern produced by a relativistically moving blob of isotropic nonthermal electrons that Thomson-scatter photons from an external isotropic radiation held goes as D-4+2 alpha. Here D is the Doppler factor, and a is the energy spectral index of the radiation. This differs from the well-known beaming pattern produced by radiation emitted isotropically in the blob frame, which is proportional to D-3+alpha. This result is important for treatments of blazar statistics, beaming constraints, and tests of gamma-ray source models.