On 2015 June 16 , Fermi -LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak > 100 MeV flux of \sim 3.6 \times 10 ^ { -5 } { photons } { cm } ^ { -2 } { s } ^ { -1 } averaged over orbital period intervals .
It is the historically highest \gamma -ray flux observed from the source including past EGRET observations , with the \gamma -ray isotropic luminosity reaching \sim 10 ^ { 49 } { erg } { s } ^ { -1 } .
During the outburst , the Fermi spacecraft , which has an orbital period of 95.4 min , was operated in a special pointing mode to optimize the exposure for 3C 279 .
For the first time , significant flux variability at sub-orbital timescales was found in blazar observations by Fermi -LAT .
The source flux variability was resolved down to 2-min binned timescales , with flux doubling times less than 5 min .
The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models .
A minimum bulk jet Lorentz factor ( \Gamma ) of 35 is necessary to avoid both internal \gamma -ray absorption and super-Eddington jet power .
In the standard external-radiation-Comptonization scenario , \Gamma should be at least 50 to avoid overproducing the synchrotron-self-Compton component .
However , this predicts extremely low magnetization ( \sim 5 \times 10 ^ { -4 } ) .
Equipartition requires \Gamma as high as 120 , unless the emitting region is a small fraction of the dissipation region .
Alternatively , we consider \gamma rays originating as synchrotron radiation of \gamma _ { e } \sim 1.6 \times 10 ^ { 6 } electrons , in magnetic field B \sim 1.3 kG , accelerated by strong electric fields E \sim B in the process of magnetoluminescence .
At such short distance scales , one can not immediately exclude production of \gamma rays in hadronic processes .