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

TL;DR

This paper reports the VERITAS detection of significant variability and an extended energy spectrum in the TeV gamma-ray emission of the distant blazar 1ES 1218+304, providing insights into its emission mechanisms and EBL absorption effects.

Contribution

First detailed variability and spectral analysis of 1ES 1218+304 at multi-TeV energies, enhancing understanding of hard-spectrum blazars.

Findings

Detected significant flux variability in 1ES 1218+304

Extended the gamma-ray spectrum into the multi-TeV range

Discussed implications for emission models and EBL absorption

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.