The brightest gamma-ray flaring blazar in the sky: AGILE and multi-wavelength observations of 3C 454.3 during November 2010

TL;DR

This paper reports on the unprecedented gamma-ray flare of blazar 3C 454.3 in November 2010, analyzing multi-wavelength data to understand its extreme brightness and variability, revealing a significant external Compton contribution.

Contribution

First comprehensive multi-wavelength analysis of the 2010 gamma-ray flare of 3C 454.3, highlighting the role of external Compton scattering in its emission.

Findings

Gamma-ray flux peaked at over 6.8e-5 ph/cm2/s, more than 6 times Vela pulsar flux.

Gamma-ray flux varied by a factor of 10, while other wavelengths varied less.

The event is similar to the 2009 outburst, with external seed photon enhancement.

Abstract

Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s on a time scale of about 12 hours, more than a factor of 6 higher than the flux of the brightest steady gamma-ray source, the Vela pulsar, and more than a factor of 3 brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make a thorough study of the present event possible: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the gamma-ray flare, we find that the radio, optical and X-ray emission varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.