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The Flat Spectrum Radio Quasar 3C 279 underwent several outbursts in the past, having flared with a peak γ-ray flux above 100 MeV (FE>100MeV) exceeding 10-5 ph cm-2 s-1, in 2013 December, 2014 April, and 2015 June. The 2013 December outburst showed an unusually hard power-law γ-ray spectrum (index~1.7), and an asymmetric light curve profile with few-hour time scale variability. This could be successfully explained using our second order Fermi acceleration model. The outburst in 2015 June was even more powerful, with FE>100MeV ~ 4 × 10-5 ph cm-2 s-1, the historically highest even when the EGRET era is included. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi-LAT, with flux doubling times of less than 5 minutes. In the standard external-Compton scenario with conical jet geometry, the minute-scale variability requires a very high bulk jet Lorentz factor (> 50) and extremely low magnetization even at the jet base (~ 100RS). However, such a high bulk jet Lorentz factor and low magnetization at the jet base pose challenges to standard models of electromagnetically driven jets. Alternately, we consider a synchrotron origin scenario for the GeV γ-ray outburst, which would work in a magnetically dominated jet. In this contribution, we present observational results of the outbursts in detail and discuss current problems on relativistic jets inferred from γ-ray observations. [ABSTRACT FROM AUTHOR]

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected a strong γ-ray flare on 2011 May 15 from a source identified through dedicated and intensive followup multifrequency observations with the core-dominated and compact flat spectrum radio quasar 4C + 49.22 (also known as S4 1150+49, SBS 1150+497, z=0.334). 4C + 49.22 was in a low γ-ray activity during the first year of Fermi survey operations and it is not included in the first Fermi - LAT Source Catalog (1FGL [1]). Simultaneous multi-wavelength observations during the transition phase including the quiescent, outburst and post-flare γ-ray states are obtained by Swift, Planck and ground-based optical observatories and radio observatories (INAOE, Catalina CSS, VLBA). The flaring state was observed also from microwaves to X-ray bands, and correlated variability is found. [ABSTRACT FROM AUTHOR]