Fermi Gamma-ray Space Telescope

Fermi LAT Detection of a Hard Spectrum Flare from the Gravitationally Lens Blazar B0218+357

Sara Buson
Teddy Cheung on behalf of the Fermi-LAT collaboration

Abstract:

The Fermi LAT has observed new gamma-ray flares from B0218+357 during July 2014. While no significant change in the gamma-ray spectrum has been previously observed through the flaring phase in late-2012, during this recent high activity the source displayed an exceptionally hard spectrum. The latter leaded to the detection of VHE (E > 100 GeV) gamma rays from B0218+357 by the MAGIC telescopes, establishing this source as the most distant TeV emitter known to date. In addition to the detection of VHE emission, this blazar is of peculiar interest since it is known to be a double-image lensed system with the lens delay of 11.46 +/- 0.16 days measured in gamma-ray. We present new Fermi LAT variability and spectral studies of the system focussed on the July 2014 flares and discuss them in the context of previous measurements.