VERITAS Discovery of Variability in the VHE Gamma-Ray Emission of 1ES 1218+304

Abstract

1ES 1218+304 is among a group of several TeV blazars that exhibit surprisingly hard energy spectra given their redshifts. The VERITAS collaboration has carried out an intensive observing campaign of 1ES 1218+304 in early 2009 to characterize the emission properties of one of these hard-spectra distant blazars in more detail. While hard-spectra TeV blazars are most promising for unveiling putative signatures from EBL absorption, they may also have implications on shock acceleration scenarios in relativistic jets. Our observations of 1ES 1218+304 demonstrate significant flux variability. Furthermore, we present an energy spectrum extending into the multi-TeV regime. The implications of these data for $\gamma$-ray emission models are discussed.