This is the first report of Fermi Gamma-ray Space Telescope observations of the quasar 3C 454.3 , which has been undergoing pronounced long-term outbursts since 2000 .
The data from the Large Area Telescope ( LAT ) , covering 2008 July 7–October 6 , indicate strong , highly variable \gamma -ray emission with an average flux of \sim 3 \times 10 ^ { -6 } photons cm ^ { -2 } s ^ { -1 } , for energies > 100 MeV .
The \gamma -ray flux is variable , with strong , distinct , symmetrically-shaped flares for which the flux increases by a factor of several on a time scale of about three days .
This variability indicates a compact emission region , and the requirement that the source is optically thin to pair-production implies relativistic beaming with Doppler factor \delta > 8 , consistent with the values inferred from VLBI observations of superluminal expansion ( \delta \sim 25 ) .
The observed \gamma -ray spectrum is not consistent with a simple power-law , but instead steepens strongly above \sim 2 GeV , and is well described by a broken power-law with photon indices of \sim 2.3 and \sim 3.5 below and above the break , respectively .
This is the first direct observation of a break in the spectrum of a high luminosity blazar above 100 MeV , and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles .
Alternatively , the spectral softening above 2 GeV could be due to \gamma -ray absorption via photon-photon pair production on the soft X-ray photon field of the host AGN , but such an interpretation would require the dissipation region to be located very close ( \lesssim 100 gravitational radii ) to the black hole , which would be inconsistent with the X-ray spectrum of the source .