Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apj...590...95l&link_type=abstract
The Astrophysical Journal, Volume 590, Issue 1, pp. 95-108.
Astronomy and Astrophysics
Astronomy
34
Galaxies: Active, Gamma Rays: Observations, Galaxies: Quasars: General, Radiation Mechanisms: Nonthermal, Radio Continuum: Galaxies
Scientific paper
We compare the Metsähovi 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.
Lahteenmaki Anne
Valtaoja Esko
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