Discovery of Very High Energy Gamma Rays from 1ES 1218+30.4

Abstract

The MAGIC collaboration has studied the high-frequency-peaked BL Lac object 1ES 1218+30.4, at a redshift z=0.182, using the MAGIC imaging air Cerenkov telescope located on the Canary Island of La Palma. A gamma-ray signal was observed with 6.4 σ significance. The differential energy spectrum for an energy threshold of 120 GeV can be fitted by a simple power law, yielding FE(E)=(8.1+/-2.1)×10-7[E/(250 GeV)]-3.0+/-0.4 TeV-1 m-2 s-1. During the 6 days of observation in 2005 January, no time variability on timescales of days was found within the statistical errors. The observed integral flux above 350 GeV is nearly a factor of 2 below the upper limit reported by the Whipple collaboration in 2003.