Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...721.1383a&link_type=abstract
The Astrophysical Journal, Volume 721, Issue 2, pp. 1383-1396 (2010).
Astronomy and Astrophysics
Astronomy
34
Galaxies: Active, Gamma Rays: Galaxies, Quasars: Individual: 3C 454.3
Scientific paper
The flat spectrum radio quasar 3C 454.3 underwent an extraordinary outburst in 2009 December when it became the brightest γ-ray source in the sky for over 1 week. Its daily flux measured with the Fermi-Large Area Telescope at photon energies E>100 MeV reached F 100 = 22 ± 1 × 10-6 photon cm-2 s-1, representing the highest daily flux of any blazar ever recorded in high-energy γ-rays. It again became the brightest source in the sky in 2010 April, triggering a pointed-mode observation by Fermi. The correlated γ-ray temporal and spectral properties during these exceptional events are presented and discussed. The main results show flux variability over time scales less than 3 hr and very mild spectral variability with an indication of gradual hardening preceding major flares. The light curves during periods of enhanced activity in 2008 July-August and 2010 December show strong resemblance, with a flux plateau of a few days preceding the major flare. No consistent loop pattern emerged in the γ-ray spectral index versus the flux plane as would be expected in acceleration and cooling scenarios. The maximum energy of a photon from 3C 454.3 is ≈20 GeV and a minimum Doppler factor of ≈13 is derived. The γ-ray spectrum of 3C 454.3 shows a significant spectral break between ≈2 and 3 GeV that is very weakly dependent on the flux state, even when the flux changes by an order of magnitude.
Ackermann Marcelo
Ajello Marco
Baldini Luca
Ballet Jean
Barbiellini Guido
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