Study of the variability of Blazars gamma-ray emission

Details Study of the variability of Blazars gamma-ray emission Study of the variability of Blazars gamma-ray emission

2011-05-13

arxiv.org/abs/1105.2649v1

Astronomy and Astrophysics

Astrophysics

High Energy Astrophysical Phenomena

11 pages, 7 figures, accepted for publication on Advances in Space Research. Poster presented at COSPAR 2010 (Bremen), event E

Scientific paper

The gamma-ray emission of blazar jets shows a pronounced variability and this feature provides limits to the size and to the speed of the emitting region. We study the gamma-ray variability of bright blazars using data from the first 18 months of activity of the Large Area Telescope on the Fermi Gamma-Ray Space Telescope. From the daily light-curves of the blazars characterized by a remarkable activity, we firstly determine the minimum variability time-scale, giving an upper limit for the size of the emitting region of the sources, assumed to be spheroidal blobs in relativistic motion. These regions must be smaller than ~10^-3 parsec. Another interesting time-scale is the duration of the outbursts. We conclude that they cannot correspond to radiation produced by a single blob moving relativistically along the jet, but they are either the signature of emission from a standing shock extracting energy from a modulated jet, or the superposition of a number of flares occurring on a shorter time-scale. We also derive lower limits on the bulk Lorentz factor needed to make the emitting region transparent for gamma-rays interacting through photon-photon collisions.

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