The December 2009 gamma-ray flare of 3C 454.3: the multifrequency campaign

TL;DR

In December 2009, the blazar 3C 454.3 exhibited a remarkable gamma-ray super-flare, monitored through a comprehensive multiwavelength campaign, revealing complex emission behaviors that challenge simple theoretical models.

Contribution

This study presents a detailed multiwavelength observational campaign of the December 2009 gamma-ray flare of 3C 454.3, highlighting the need for additional particle components in emission models.

Findings

Detected a gamma-ray super-flare with peak flux ~2000E-8 ph/cm2/s.

Observed a lack of strong optical brightening during the gamma-ray flare.

Identified the limitations of a one-zone emission model for the flare spectra.

Abstract

During the month of December, 2009 the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F ~2000E-8 ph/cm2/s for E > 100 MeV. Starting in November, 2009 intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here we report the results of a 2-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, RossiXTE for the high-energy observations, and Swift/UVOT, KANATA, GRT, REM for the near-IR/optical/UV data. The GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting ~1 month at all wavelengths: in the gamma-ray band, peak emission was reached on December 2-3, 2009. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broad-band spectral evolution severely constrain the theoretical modelling. We find that the pre- and post-flare broad-band behavior can be explained by a one-zone model involving SSC plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the Dec. 2-3, 2009 super-flare and of the secondary peak emission on Dec. 9, 2009 cannot be satisfactorily modelled by a simple one-zone model. An additional particle component is most likely active during these states.