The 2009 December Gamma-ray Flare of 3C 454.3: The Multifrequency Campaign

Abstract

During the month of 2009 December, the blazar 3C 454.3 became the brightest gamma-ray source in the sky,reaching a peak flux F ~ 2000 × 10-8 photons cm-2 s-1 for E > 100 MeV. Starting in 2009 Novemberintensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here, we report on the results ofa two-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, and Rossi XTE for the high-energyobservations and Swift/UVOT, KANATA, Goddard Robotic Telescope, and REM for the near-IR/optical/UVdata. GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phaselasting ~1 month at all wavelengths: in the gamma-ray band, peak emission was reached on 2009 December2–3. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in theoptical/UV band that reached a level substantially lower than the previous observations in 2007–2008. The lackof strong simultaneous optical brightening during the super-flare and the determination of the broadband spectralevolution severely constrain the theoretical modeling. We find that the pre- and post-flare broadband behavior canbe explained by a one-zone model involving synchrotron self-Compton plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the 2009 December 2–3 super-flare and of thesecondary peak emission on 2009 December 9 cannot be satisfactorily modeled by a simple one-zone model. Anadditional particle component is most likely active during these states.