Discovery of very high energy gamma rays from 1ES 1218+30.4
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2006
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IOP Publishing
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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 sigma significance. The differential energy spectrum for an energy threshold of 120 GeV can be fitted by a simple power law, yielding F-E = (8.1 +/- 2.1) x 10(-7)[E/(250 GeV)](-3.0 +/- 0.4) TeV-1 F (E) 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.
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© The American Astronomical Society. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German Bundesministerium für Bildung und Forschung and
Max-Planck-Gesellschaft, the Italian Istituto Nazionale de Fisica Nucleare, and the Spanish Comisión Interministerial de Ciencias y Tecnología is gratefully acknowledged. This work was also supported by ETH Research Grant TH 34/04 3 and
grant 1P03D01028 from the Polish Ministerstwo Nauki i
Informatyzacji.