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Discovery of variability in the very high energy γ-ray emission of 1es 1218+304 with veritas
Acciari, V. A.; Aliu, E.; Beilicke, M.; Benbow, W.; Boltuch, D.; Böttcher, M.; Bradbury, S. M.; Bugaev, V.; Byrum, K.; Cesarini, A.; Ciupik, L.; Cogan, P.; Cui, W.; Dickherber, R.; Duke, C.; Falcone, A.; Finley, J. P.; Finnegan, G.; Fortson, L.; Furniss, A.
We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES 1218+304 was detected previously by MAGIC and VERITAS at a persistent level of similar to 6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare reaching similar to 20% of the Crab. While very high energy (VHE) flares are quite common in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is particularly interesting since it belongs to a group of blazars that exhibit unusually hard VHE spectra considering their redshifts. When correcting the measured spectra for absorption by the extragalactic background light, 1ES 1218+304 and a number of other blazars are found to have differential photon indices Gamma <= 1.5. The difficulty in modeling these hard spectral energy distributions in blazar jets has led to a range of theoretical gamma-ray emission scenarios, one of which is strongly constrained by these new VERITAS observations. We consider the implications of the observed light curve of 1ES 1218+304, which shows day scale flux variations, for shock acceleration scenarios in relativistic jets, and in particular for the viability of kiloparsec-scale jet emission scenarios.
Keyword(s): bl lacertae objects individual (1es 1218+304=ver j1221+301); galaxies active; gamma rays galaxies; active galactic nuclei; extragalactic background light; peaked bl-lacertae; w-comae; blazars; spectra; acceleration; jet; constraints; telescope
Publication Date:
Type: Journal article
Peer-Reviewed: Unknown
Institution: NUI Galway
Publisher(s): IOP Publishing
First Indexed: 2019-03-23 06:50:52 Last Updated: 2019-09-20 07:01:42