MINUTE-TIMESCALE >100 MeV γ -RAY VARIABILITY DURING THE GIANT OUTBURST OF QUASAR 3C 279 OBSERVED BY FERMI -LAT IN 2015 JUNE
- Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
- W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
- Institute for Cosmic-Ray Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8582 (Japan)
- Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
- NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy)
- Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
- INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano (Italy)
- Agenzia Spaziale Italiana (ASI) Science Data Center, I-00133 Roma (Italy)
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{sup −5} photons cm{sup −2} s{sup −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 ∼10{sup 49} erg s{sup −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{sup −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 {sub e} ∼ 1.6 × 10{sup 6} 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.
- OSTI ID:
- 22654297
- Journal Information:
- Astrophysical Journal Letters, Vol. 824, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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