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.
MINUTE-TIMESCALE >100 MeV gamma-RAY VARIABILITY during the GIANT OUTBURST of QUASAR 3C 279 OBSERVED by FERMI-LAT in 2015 June / Ackermann, M; Anantua, R.; Asano, K.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Gonzalez, J. Becerra; Bellazzini, R.; Bissaldi, Elisabetta; 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, Cecilia; Fegan, S. J.; Ferrara, E. C.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, Nicola; 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.; Sgr, 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.. - In: THE ASTROPHYSICAL JOURNAL LETTERS. - ISSN 2041-8205. - STAMPA. - 824:2(2016). [10.3847/2041-8205/824/2/L20]
MINUTE-TIMESCALE >100 MeV gamma-RAY VARIABILITY during the GIANT OUTBURST of QUASAR 3C 279 OBSERVED by FERMI-LAT in 2015 June
BISSALDI, Elisabetta;FAVUZZI, Cecilia;GIGLIETTO, Nicola;
2016-01-01
Abstract
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
