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American Astronomical Society, Astrophysical Journal, 2(693), p. L104-L108, 2009

DOI: 10.1088/0004-637x/693/2/l104

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VERITAS OBSERVATIONS OF a VERY HIGH ENERGY γ-Ray FLARE FROM THE BLAZAR 3C 66A

Journal article published in 2009 by A. Cannon, O. Celik, A. Cesarini, Y. C. Chow, L. Ciupik, P. Cogan, W. Cui, M. K. Daniel, R. Dickherber, T. Ergin, A. Falcone, S. J. Fegan, J. P. Finley, P. Fortin, L. Fortson and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) gamma-rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 events is detected, corresponding to a significance of 21.2 standard deviations (sigma), in these observations (32.8 hours live time). The observed integral flux above 200 GeV is 6% of the Crab Nebula's flux and shows evidence for variability on the time-scale of days. The measured energy spectrum is characterized by a soft power law with photon index Gamma = 4.1 +- 0.4_stat +- 0.6_sys. The radio galaxy 3C 66B is excluded as a possible source of the VHE emission. ; Comment: 13 Pages, 4 Figures. Published in ApJL. This new version correctly calculates the intrinsic photon index (see Erratum: ApJL, 721:L203-L204)