VERITAS Observations of a Very High Energy Gamma-ray Flare from the Blazar 3C 66A

📝 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.

💡 Analysis

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.

📄 Content

arXiv:0901.4527v2 [astro-ph.HE] 10 Dec 2010 VERITAS Observations of a Very High Energy γ-ray Flare from the Blazar 3C 66A V. A. Acciari1, E. Aliu2, T. Arlen3, M. Beilicke4, W. Benbow5, M. B¨ottcher6, S. M. Bradbury7, J. H. Buckley4, V. Bugaev4, Y. Butt8, K. Byrum9, A. Cannon10, O. Celik3, A. Cesarini11, Y. C. Chow3, L. Ciupik12, P. Cogan13, W. Cui14, M. K. Daniel7,†, R. Dickherber4, T. Ergin8, A. Falcone15, S. J. Fegan3, J. P. Finley14, P. Fortin16, L. Fortson12, A. Furniss17, D. Gall14, K. Gibbs5, G. H. Gillanders11, S. Godambe18, J. Grube10, R. Guenette13, G. Gyuk12, D. Hanna13, E. Hays19, J. Holder2, D. Horan20, C. M. Hui18, T. B. Humensky21, A. Imran22, P. Kaaret23, N. Karlsson12, M. Kertzman24, D. Kieda18, J. Kildea5, A. Konopelko25, H. Krawczynski4, F. Krennrich22, M. J. Lang11, S. LeBohec18, G. Maier13, A. McCann13, M. McCutcheon13, J. Millis26, P. Moriarty1, R. Mukherjee16, T. Nagai22, R. A. Ong3, A. N. Otte17, D. Pandel23, J. S. Perkins5,∗, D. Petry27, F. Pizlo14, M. Pohl22, J. Quinn10, K. Ragan13, L. C. Reyes28, P. T. Reynolds29, E. Roache5, H. J. Rose7, M. Schroedter22, G. H. Sembroski14, A. W. Smith9, D. Steele12, S. P. Swordy21, M. Theiling5, J. A. Toner11, A. Varlotta14, V. V. Vassiliev3, R. G. Wagner9, S. P. Wakely21, J. E. Ward10, T. C. Weekes5, A. Weinstein3, D. A. Williams17, S. Wissel21, M. Wood3, B. Zitzer14 – 2 – 1Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland 2Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA 3Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA 4Department of Physics, Washington University, St. Louis, MO 63130, USA 5Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA 6Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 7School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK 8Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 9Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA 10School of Physics, University College Dublin, Belfield, Dublin 4, Ireland 11School of Physics, National University of Ireland, Galway, Ireland 12Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA 13Physics Department, McGill University, Montreal, QC H3A 2T8, Canada 14Department of Physics, Purdue University, West Lafayette, IN 47907, USA 15Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA 16Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA 17Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA 18Physics Department, University of Utah, Salt Lake City, UT 84112, USA 19N.A.S.A./Goddard Space-Flight Center, Code 661, Greenbelt, MD 20771, USA 20Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau, France 21Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA 22Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA 23Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA 24Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA 25Department of Physics, Pittsburg State University, 1701 South Broadway, Pittsburg, KS 66762, USA 26Department of Physics, Anderson University, 1100 East 5th Street, Anderson, IN 46012 27European Southern Observatory, Karl-Schwarzchild-Strasse 2, 85748 Garching, Germany 28Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA 29Department of Applied Physics and Instumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland †Now at: Department of Physics, Durham University, South Road, Durham, DH1 3LE, U.K. *Corresponding author: jperkins@cfa.harvard.edu – 3 – ABSTRACT The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) γ-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 (σ), 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 Γ = 4.1±0.4stat ±0.6sys. The radio galaxy 3C 66B is excluded as a possible source of the VHE emission. Subject headings: galaxies: active — BL Lacertae objects: individual (3C 66A) — gamma rays: observations 1. Introduction Wills & Wills (1974) first identified 3C 66A as a QSO using optical observations. It was subse

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