Abstract
Recent detection of suborbital gamma-ray variability of Flat Spectrum Radio Quasar (FSRQ) 3C 279 by Fermi Large Area Telescope (LAT) is in severe conflict with established models of blazar emission. This paper presents the results of suborbital analysis of the Fermi/LAT data for the brightest gamma-ray flare of another FSRQ blazar 3C 454.3 in November 2010 (Modified Julian Date; MJD 55516-22). Gamma-ray light curves are calculated for characteristic time bin lengths as short as 3 min. The measured variations of the 0.1–10 GeV photon flux are tested against the hypothesis of steady intraorbit flux. In addition, the structure function is calculated for absolute photon flux differences and for their significances. Significant gamma-ray flux variations are measured only over time scales longer than ∼5 h, which is consistent with the standard blazar models.
Highlights
Blazars—active galaxies with relativistically beamed non-thermal broad-band emission—belong to the brightest gamma-ray sources in the sky
Such a short variability time scale is much shorter than the light-crossing time tbh ∼ 3Mbh,9 h of supermassive black holes located at the bases of relativistic jets of blazars
Additional challenges arise in the case of the most luminous blazars known as flat spectrum radio quasars (FSRQs) due to the presence of dense radiation fields that provide a target for external absorption of gamma rays [8,9]
Summary
Blazars—active galaxies with relativistically beamed non-thermal broad-band emission—belong to the brightest gamma-ray sources in the sky. Before the launch of Fermi, the shortest variability time scales of tvar ∼ 2 min were measured in the very-high-energy (VHE) gamma rays above 100 GeV by ground-based Cherenkov telescopes, in particular by H.E.S.S. in PKS 2155-304 [3] and by MAGIC in Mrk 501 [4]. Such a short variability time scale is much shorter than the light-crossing time tbh ∼ 3Mbh, h of supermassive black holes located at the bases of relativistic jets of blazars. In order to avoid such absorption, one can consider highly relativistic bulk motions with Lorentz factors Γ ∼ 100 [10] or possibly conversion of gamma-ray photons into axions [11]
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