Synchrotron emission from shock waves in active galactic nuclei

Abstract

The origin of the sharp near-infrared cutoff in the continuous energy distribution of many compact nonthermal sources (BL Lacs, OVVs, red quasars, and certain jets) is considered under the assumption that particle acceleration takes place in shocks. Energy losses due to synchrotron emission and photon interactions are taken into account and set upper limits to the possible electron and proton energies. In these circumstances, the upstream disturbance to the flow is dominated by the most energetic protons which are postulated to excite a turbulent wave spectrum of Kolmogorov type in this region. This in turn sets the relative acceleration times for all particles as a function of energy. This model predicts a highest frequency nu-asterisk of electron synchrotron emission which depends principally on the shock velocity and the ratio a of photon to magnetic energy density in the acceleration region. For near relativistic flows and reasonable values of a, a spectral cutoff is predicted in the range of nu between 3 x 10 to the 14th and 2 x 10 to the 15th Hz. Other consequences of this model are briefly discussed.