Testing of Inverse Compton Models for Active Galactic Nuclei with Gamma‐Ray and Radio Observations

Abstract

We compare the Metsahovi 22 and 37 GHz total flux density variation data of active galactic nuclei with EGRET (on board the Compton Gamma Ray Observatory) gamma-ray observations from Cycles 1-4. Statistical analysis reveals that there is a genuine connection between the high-frequency radio properties of the sources, e.g., the type of the source, the phase of the radio flare, the associated radio variability brightness temperature, and the gamma-ray emission. Typically the most likely gamma-ray emitter is a high optical polarization quasar with a large Doppler boosting factor. The highest levels of gamma-ray emission are observed during the initial (or peak) stages of high-frequency radio flares. BL Lac objects are much weaker gamma-ray emitters, with no clear correlation between radio and gamma variations. We calculate the distance of the gamma-ray-emitting region from the core in quasars and obtain an average value of 4.9 pc, well downstream from the accretion disk or the broad-line region. This indicates that the strongest time-dependent gamma-ray emission of quasars originates in the relativistic jet, within the same shocks that produce the synchrotron flares at radio frequencies induced by the synchrotron self-Compton mechanism. Weaker gamma-ray emission does not seem to be associated with shocks and may be caused by other mechanisms, such as external Compton processes.