Minute-timescale >100 MeV gamma-Ray Variability during the Giant Outburst of Quasar 3C 279 Observed by Fermi-LAT in 2015 June

Ackermann, M.M.AckermannAnantua, R.R.AnantuaAsano, K.K.AsanoCavazzuti, ElisabettaElisabettaCavazzutiCiprini, StefanoStefanoCipriniCutini, SaraSaraCutiniGasparrini, DarioDarioGasparrini2020-09-172020-09-172016-06-01https://hdl.handle.net/20.500.13025/4768The Astrophysical Journal Letters, Volume 824, Issue 2, article id. L20, <NUMPAGES></NUMPAGES> pp. (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 gamma-ray flux observed from the source, including past EGRET observations, with the gamma-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 (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 (~5 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 ~ 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 gamma-rays in hadronic processes.galaxies activegalaxies jetsgamma rays galaxiesquasars individual 3C 279radiation mechanisms non-thermalMinute-timescale >100 MeV gamma-Ray Variability during the Giant Outburst of Quasar 3C 279 Observed by Fermi-LAT in 2015 June10.3847/2041-8205/824/2/L20http://adsabs.harvard.edu/abs/2016ApJ...824L..20A2016ApJ...824L..20A