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Title: VERITAS 2008-2009 MONITORING OF THE VARIABLE GAMMA-RAY SOURCE M 87

M 87 is a nearby radio galaxy that is detected at energies ranging from radio to very high energy (VHE) gamma rays. Its proximity and its jet, misaligned from our line of sight, enable detailed morphological studies and extensive modeling at radio, optical, and X-ray energies. Flaring activity was observed at all energies, and multi-wavelength correlations would help clarify the origin of the VHE emission. In this paper, we describe a detailed temporal and spectral analysis of the VERITAS VHE gamma-ray observations of M 87 in 2008 and 2009. In the 2008 observing season, VERITAS detected an excess with a statistical significance of 7.2 standard deviations ({sigma}) from M 87 during a joint multi-wavelength monitoring campaign conducted by three major VHE experiments along with the Chandra X-ray Observatory. In 2008 February, VERITAS observed a VHE flare from M 87 occurring over a 4 day timespan. The peak nightly flux above 250 GeV was (1.14 {+-} 0.26) x 10{sup -11} cm{sup -2} s{sup -1}, which corresponded to 7.7% of the Crab Nebula flux. M 87 was marginally detected before this 4 day flare period, and was not detected afterward. Spectral analysis of the VERITAS observations showed no significant change in themore » photon index between the flare and pre-flare states. Shortly after the VHE flare seen by VERITAS, the Chandra X-ray Observatory detected the flux from the core of M 87 at a historical maximum, while the flux from the nearby knot HST-1 remained quiescent. Acciari et al. presented the 2008 contemporaneous VHE gamma-ray, Chandra X-ray, and Very Long Baseline Array radio observations which suggest the core as the most likely source of VHE emission, in contrast to the 2005 VHE flare that was simultaneous with an X-ray flare in the HST-1 knot. In 2009, VERITAS continued its monitoring of M 87 and marginally detected a 4.2{sigma} excess corresponding to a flux of {approx}1% of the Crab Nebula. No VHE flaring activity was observed in 2009.« less
Authors:
;  [1] ;  [2] ; ;  [3] ;  [4] ; ; ; ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ; ;  [13] ;  [14]
  1. Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
  2. Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States)
  3. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
  4. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
  5. Department of Physics, Washington University, St. Louis, MO 63130 (United States)
  6. Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
  7. School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT (United Kingdom)
  8. Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)
  9. School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)
  10. School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
  11. Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
  12. Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
  13. Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
  14. Department of Physics, Grinnell College, Grinnell, IA 50112-1690 (United States)
Publication Date:
OSTI Identifier:
21451112
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 716; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/716/1/819
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC GAMMA SOURCES; CRAB NEBULA; FLARING; GAMMA RADIATION; PHOTON EMISSION; PHOTONS; RADIO GALAXIES; WAVELENGTHS BOSONS; COSMIC RADIO SOURCES; COSMIC RAY SOURCES; ELECTROMAGNETIC RADIATION; ELEMENTARY PARTICLES; EMISSION; GALAXIES; IONIZING RADIATIONS; MASSLESS PARTICLES; NEBULAE; RADIATIONS; SUPERNOVA REMNANTS