Search for the shortest variability at gamma rays in flat-spectrum radio quasars

Abstract

We report about the search for short-term variability in the high-energy γ-ray energy band of three flat-spectrum radio quasars (3C 454.3, 3C 273, PKS B1222 + 216), whose flux at E > 100 MeV exceeded the value of 10 -5 ph cm-2 s-1 for at least one day. Although, the statistics was not yet sufficient to effectively measure the characteristic time scale, it allowed us to set tight upper limits on the observed doubling time scale (<2-3 h) - the smallest measured to date at MeV energies -, which can constrain the size of the γ-ray emitting region. The results obtained in the present work favor the hypothesis that γ rays are generated inside the broad-line region. © 2011 ESO.