Observation of Gamma-Ray Emission from the Galaxy M87 above 250 GeV with VERITAS*

V. A. Acciari; M. Beilicke; G. Blaylock; S. M. Bradbury; J. H. Buckley; V. Bugaev; Y. Butt; O. Celik; A. Cesarini; L. Ciupik; P. Cogan; P. Colin; W. Cui; M. K. Daniel; C. Duke; T. Ergin; A. D. Falcone; S. J. Fegan; J. P. Finley; G. Finnegan; P. Fortin; L. F. Fortson; K. Gibbs; G. H. Gillanders; J. Grube; R. Guenette; G. Gyuk; D. Hanna; E. Hays; J. Holder; D. Horan; S. B. Hughes; M. C. Hui; T. B. Humensky; A. Imran; P. Kaaret; M. Kertzman; D. B. Kieda; J. Kildea; A. Konopelko; H. Krawczynski; F. Krennrich; M. J. Lang; S. LeBohec; K. Lee; G. Maier; A. McCann; M. McCutcheon; J. Millis; P. Moriarty; R. Mukherjee; T. Nagai; R. A. Ong; D. Pandel; J. S. Perkins; M. Pohl; J. Quinn; K. Ragan; P. T. Reynolds; H. J. Rose; M. Schroedter; G. H. Sembroski; A. W. Smith; D. Steele; S. P. Swordy; A. Syson; J. A. Toner; L. Valcarcel; V. V. Vassiliev; S. P. Wakely; J. E. Ward; T. C. Weekes; A. Weinstein; R. J. White; D. A. Williams; S. A. Wissel; M. D. Wood; B. Zitzer

doi:10.1086/587458

Observation of Gamma-Ray Emission from the Galaxy M87 above 250 GeV with VERITAS^*

V. A. Acciari¹, M. Beilicke², G. Blaylock³, S. M. Bradbury⁴, J. H. Buckley², V. Bugaev², Y. Butt⁵, O. Celik⁶, A. Cesarini⁷, L. Ciupik⁸, P. Cogan⁹, P. Colin¹⁰, W. Cui¹¹, M. K. Daniel⁴, C. Duke¹², T. Ergin³, A. D. Falcone¹³, S. J. Fegan⁶, J. P. Finley¹¹, G. Finnegan¹⁰, P. Fortin¹⁴, L. F. Fortson⁸, K. Gibbs⁵, G. H. Gillanders⁷, J. Grube⁴, R. Guenette⁹, G. Gyuk⁸, D. Hanna⁹, E. Hays^15,16,17, J. Holder¹⁸, D. Horan¹⁶, S. B. Hughes², M. C. Hui¹, T. B. Humensky¹⁵, A. Imran¹⁹, P. Kaaret²⁰, M. Kertzman²¹, D. B. Kieda¹⁰, J. Kildea⁵, A. Konopelko¹¹, H. Krawczynski², F. Krennrich¹⁹, M. J. Lang⁷, S. LeBohec¹⁰, K. Lee², G. Maier⁹, A. McCann⁹, M. McCutcheon⁹, J. Millis¹¹, P. Moriarty¹, R. Mukherjee¹⁴, T. Nagai¹⁹, R. A. Ong⁶, D. Pandel²⁰, J. S. Perkins⁵, M. Pohl¹⁹, J. Quinn²², K. Ragan⁹, P. T. Reynolds²³, H. J. Rose⁴, M. Schroedter¹⁹, G. H. Sembroski¹¹, A. W. Smith⁴, D. Steele⁸, S. P. Swordy¹⁵, A. Syson⁴, J. A. Toner⁷, L. Valcarcel⁹, V. V. Vassiliev⁶, S. P. Wakely¹⁵, J. E. Ward²², T. C. Weekes⁵, A. Weinstein⁶, R. J. White⁴, D. A. Williams²⁴, S. A. Wissel¹⁵, M. D. Wood⁶, and B. Zitzer¹¹

© 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.
The Astrophysical Journal, Volume 679, Number 1 Citation V. A. Acciari et al 2008 ApJ 679 397 DOI 10.1086/587458

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¹ Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Galway, Ireland

² Department of Physics, Washington University, St. Louis, MO 63130

³ Department of Physics, University of Massachusetts, Amherst, MA 01003

⁴ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, England UK

⁵ Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645

⁶ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095

⁷ Physics Department, National University of Ireland, Galway, Ireland

⁸ Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605

⁹ Physics Department, McGill University, Montreal, QC H3A 2T8, Canada

¹⁰ Department of Physics, University of Utah, Salt Lake City, UT 84112

¹¹ Department of Physics, Purdue University, West Lafayette, IN 47907

¹² Department of Physics, Grinnell College, Grinnell, IA 50112-1690

¹³ Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802

¹⁴ Department of Physics and Astronomy, Barnard College, Columbia University, New York, NY 10027

¹⁵ Enrico Fermi Institute, University of Chicago, Chicago, IL 60637

¹⁶ Argonne National Laboratory, Argonne, IL 60439

¹⁷ Current address: NASA Goddard Space Flight Center, Greenbelt, MD 20771

¹⁸ Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716

¹⁹ Department of Physics and Astronomy, Iowa State University, Ames, IA 50011

²⁰ Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242

²¹ Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037

²² School of Physics, University College Dublin, Belfield, Dublin 4, Ireland

²³ Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland

²⁴ Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064

Dates

Received 2007 December 11
Accepted 2008 February 11

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Abstract

The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring in active galactic nuclei from radio waves to TeV γ-rays. Here we report the detection of γ-ray emission above 250 GeV from M87 in spring 2007 with the VERITAS atmospheric Cerenkov telescope array and discuss its correlation with the X-ray emission. The γ-ray emission is measured to be pointlike with an intrinsic source radius less than 4.5^'. The differential energy spectrum is fitted well by a power-law function: dΦ/dE = (7.4 ± 1.3_stat ± 1.5_sys)(E/TeV)^{(− 2.31 ± 0.17stat ± 0.2sys)} 10⁻⁹ m⁻² s⁻¹ TeV⁻¹. We show strong evidence for a year-scale correlation between the γ-ray flux reported by TeV experiments and the X-ray emission measured by the ASM RXTE observatory, and discuss the possible short-timescale variability. These results imply that the γ-ray emission from M87 is more likely associated with the core of the galaxy than with other bright X-ray features in the jet.

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