L. Foschini, G. Ghisellini, F. Tavecchio, G. Bonnoli, A. Stamerra
We studied the rapid variability at GeV gamma rays of the flat-spectrum radio
quasar PKS 1222+216, which was recently found by the MAGIC Cerenkov telescope
to display very short variability (minutes time scale) at hundreds of GeV. We
analyzed the time period between 2010 April 29 and June 20, when the source
generated a few gamma-ray flares with flux in the MeV-GeV band in excess of
10^-5 ph cm^-2 s^-1 on daily basis. We set tight upper limits on the observed
doubling time scale (0.8 hours on 2010 April 30), the smallest measured to date
at MeV-GeV energies, which can constrain the size of the gamma-ray emitting
region. We also studied the spectra measured during two flares (2010 April 30
and June 17-18). The combination of spectral and variability studies obtained
in the present work favors the hypothesis that gamma rays are generally
produced inside the broad-line region (BLR), but sometimes the dissipation can
occur at larger distances, nearby the infrared torus.
View original:
http://arxiv.org/abs/1110.4471
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