We have compared the radio emission from a sample of parsec-scale AGN jets as measured by the VLBA at 15 GHz, with their associated gamma-ray properties that are reported in the Fermi LAT 3-month bright source list. We find in our radio-selected sample that the gamma-ray photon flux correlates well with the quasi-simultaneously measured compact radio flux density. The LAT-detected jets in our radio-selected complete sample generally have higher compact radio flux densities, and their parsec-scale cores are brighter (i.e., have higher brightness temperature) than the jets in the LAT non-detected objects. This suggests that the jets of bright gamma-ray AGN have preferentially higher Doppler-boosting factors. In addition, AGN jets tend to be found in a more active radio state within several months from LAT-detection of their strong gamma-ray emission. This result becomes more pronounced for confirmed gamma-ray flaring sources. We identify the parsec-scale radio core as a likely location for both the gamma-ray and radio flares, which appear within typical timescales of up to a few months of each other.
@article{arxiv.0902.2085,
title = {On the relation between AGN gamma-ray emission and parsec-scale radio jets},
author = {Y. Y. Kovalev and H. D. Aller and M. F. Aller and D. C. Homan and M. Kadler and K. I. Kellermann and Yu. A. Kovalev and M. L. Lister and M. J. McCormick and A. B. Pushkarev and E. Ros and J. A. Zensus},
journal= {arXiv preprint arXiv:0902.2085},
year = {2009}
}
Comments
5 pages, 5 figures, accepted for publication in the Astrophysical Journal Letters; title is changed, minor corrections of the text are made