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

Understand

The Fermi-LAT has observed new gamma-ray flares from the blazar 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 led to the detection of very high energy (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 particular interest since it is known to be a double-image gravitationally lensed system with a lens delay of 11.46 +/- 0.16 days measured in gamma-rays.