Fermi Gamma-ray Space Telescope Observations of Recent Gamma-ray Outbursts from 3C 454.3

TL;DR

This paper reports on the Fermi telescope's observations of extraordinary gamma-ray outbursts from the quasar 3C 454.3 in 2009-2010, highlighting extreme flux variability, spectral properties, and implications for blazar emission models.

Contribution

It provides detailed gamma-ray temporal and spectral analysis of the brightest blazar outbursts observed by Fermi, revealing new insights into variability and spectral features.

Findings

Flux variability on timescales less than 3 hours

Mild spectral variability with gradual hardening before flares

Maximum photon energy around 20 GeV

Abstract

The flat spectrum radio quasar 3C~454.3 underwent an extraordinary outburst in December 2009 when it became the brightest gamma-ray source in the sky for over one week. Its daily flux measured with the Fermi Large Area Telescope at photon energies E>100 MeV reached F = 22+/-1 x 10^-6 ph cm^-2 s^-1, representing the highest daily flux of any blazar ever recorded in high-energy gamma-rays. It again became the brightest source in the sky in 2010 April, triggering a pointed-mode observation by Fermi. The correlated gamma-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 h and very mild spectral variability with an indication of gradual hardening preceding major flares. No consistent loop pattern emerged in the gamma-ray spectral index vs flux plane. A minimum Doppler factor of ~ 15 is derived, and the maximum energy of a photon from 3C 454.3 is ~ 20 GeV. The spectral break at a few GeV is inconsistent with Klein-Nishina softening from power-law electrons scattering Ly_alpha line radiation, and a break in the underlying electron spectrum in blazar leptonic models is implied.