MINUTE-TIMESCALE >100 MeV γ-RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI-LAT IN 2015 JUNE
Authors: Ackermann M. , Anantua R. , Asano K. , Baldini L. , Barbiellini G. , Bastieri D. , Gonzalez J. Becerra , Bellazzini R. , Bissaldi E. , Blandford R. D. , Bloom E. D. , Bonino R. , Bottacini E. , Bruel P. , Buehler R. , Caliandro G. A. , Cameron R. A. , Caragiulo M. , Caraveo P. A. , Cavazzuti E. , Cecchi C. , Cheung C. C. , Chiang J. , Chiaro G. , Ciprini S. , Cohen-Tanugi J. , Costanza F. , Cutini S. , D’Ammando F. , Palma F. de , Desiante R. , Digel S. W. , Lalla N. Di , Mauro M. Di , Venere L. Di , Drell P. S. , Favuzzi C. , Fegan S. J. , Ferrara E. C. , Fukazawa Y. , Funk S. , Fusco P. , Gargano F. , Gasparrini D. , Giglietto N. , Giordano F. , Giroletti M. , Grenier I. A. , Guillemot L. , Guiriec S. , Hayashida M. , Hays E. , Horan D. , Jóhannesson G. , Kensei S. , Kocevski D. , Kuss M. , Mura G. La , Larsson S. , Latronico L. , Li J. , Longo F. , Loparco F. , Lott B. , Lovellette M. N. , Lubrano P. , Madejski G. M. , Magill J. D. , Maldera S. , Manfreda A. , Mayer M. , Mazziotta M. N. , Michelson P. F. , Mirabal N. , Mizuno T. , Monzani M. E. , Morselli A. , Moskalenko I. V. , Nalewajko K. , Negro M. , Nuss E. , Ohsugi T. , Orlando E. , Paneque D. , Perkins J. S. , Pesce-Rollins M. , Piron F. , Pivato G. , Porter T. A. , Principe G. , Rando R. , Razzano M. , Razzaque S. , Reimer A. , Scargle J. D. , Sgrò C. , Sikora M. , Simone D. , Siskind E. J. , Spada F. , Spinelli P. , Stawarz L. , Thayer J. B. , Thompson D. J. , Torres D. F. , Troja E. , Uchiyama Y. , Yuan Y. , Zimmer S. 
Published: June 2016

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 ∼3.6 × 10−5 photons cm−2 s−1, averaged over orbital period intervals. It is historically the highest γ-ray flux observed from the source, including past EGRET observations, with the γ-ray isotropic luminosity reaching ∼1049 erg s−1. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 minutes, 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-minute binned timescales, with flux doubling times of less than 5 minutes. 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 (Γ) of 35 is necessary to avoid both internal γ-ray absorption and super-Eddington jet power. In the standard external radiation Comptonization scenario, Γ should be at least 50 to avoid overproducing the synchrotron self-Compton component. However, this predicts extremely low magnetization (∼5 × 10−4). Equipartition requires Γ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider γ rays originating as synchrotron radiation of γ
e ∼ 1.6 × 106 electrons, in a magnetic field B ∼ 1.3 kG, accelerated by strong electric fields E ∼ B in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude the production of γ-rays in hadronic processes.