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arXiv · 1005.0367

VERITAS 2008 - 2009 monitoring of the variable gamma-ray source M87

The VERITAS Collaboration·V. A. Acciari·E. Aliu·T. Arlen·T. Aune·M. Beilicke·W. Benbow·D. Boltuch·S. M. Bradbury·J. H. Buckley·V. Bugaev·K. Byrum·A. Cannon·A. Cesarini·Y. C. Chow·L. Ciupik·P. Cogan·W. Cui·R. Dickherber·C. Duke·J. P. Finley·G. Finnegan·P. Fortin·L. Fortson·A. Furniss·N. Galante·D. Gall·G. H. Gillanders·S. Godambe·J. Grube·R. Guenette·G. Gyuk·D. Hanna·J. Holder·C. M. Hui·T. B. Humensky·A. Imran·P. Kaaret·N. Karlsson·M. Kertzman·D. Kieda·A. Konopelko·H. Krawczynski·F. Krennrich·M. J. Lang·S. LeBohec·G. Maier·S. McArthur·A. McCann·M. McCutcheon·J. Millis·P. Moriarty·R. A. Ong·A. N. Otte·D. Pandel·J. S. Perkins·A. M. J. Quinn·K. Ragan·L. C. Reyes·P. T. Reynolds·E. Roache·H. J. Rose·A. C. Rovero·M. Schroedter·G. H. Sembroski·G. Demet Senturk·A. W. Smith·D. Steele·S. P. Swordy·M. Theiling·S. Thibadeau·A. Varlotta·S. Vincent·R. G. Wagner·S. P. Wakely·J. E. Ward·T. C. Weekes·A. Weinstein·T. Weisgarber·D. A. Williams·S. Wissel·M. Wood·B. Zitzer·Chandra M87 Monitoring·:·D. E. Harris·F. Massaro
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Abstract

M87 is a nearby radio galaxy that is detected at energies ranging from radio to 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 M87 in 2008 and 2009. In the 2008 observing season, VERITAS detected an excess with a statistical significance of 7.2 sigma from M87 during a joint multi-wavelength monitoring campaign conducted by three major VHE experiments along with the Chandra X-ray Observatory. In February 2008, VERITAS observed a VHE flare from M87 occurring over a 4-day timespan. The peak nightly flux above 250GeV was 7.7% of the Crab Nebula flux. M87 was marginally detected before this 4-day flare period, and was not detected afterwards. Spectral analysis of the VERITAS observations showed no significant change in the 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 M87 at a historical maximum, while the flux from the nearby knot HST-1 remained quiescent. Acciari et al. (2009) presented the 2008 contemporaneous VHE gamma-ray, Chandra X-ray, and VLBA 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 M87 and marginally detected a 4.2 sigma excess corresponding to a flux of ~1% of the Crab Nebula. No VHE flaring activity was observed in 2009.

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The VERITAS Collaboration, V. A. Acciari, E. Aliu, T. Arlen, T. Aune, M. Beilicke, W. Benbow, D. Boltuch, S. M. Bradbury, J. H. Buckley, V. Bugaev, K. Byrum, A. Cannon, A. Cesarini, Y. C. Chow, L. Ciupik, P. Cogan, W. Cui, R. Dickherber, C. Duke, J. P. Finley, G. Finnegan, P. Fortin, L. Fortson, A. Furniss, N. Galante, D. Gall, G. H. Gillanders, S. Godambe, J. Grube, R. Guenette, G. Gyuk, D. Hanna, J. Holder, C. M. Hui, T. B. Humensky, A. Imran, P. Kaaret, N. Karlsson, M. Kertzman, D. Kieda, A. Konopelko, H. Krawczynski, F. Krennrich, M. J. Lang, S. LeBohec, G. Maier, S. McArthur, A. McCann, M. McCutcheon, J. Millis, P. Moriarty, R. A. Ong, A. N. Otte, D. Pandel, J. S. Perkins, A. M. J. Quinn, K. Ragan, L. C. Reyes, P. T. Reynolds, E. Roache, H. J. Rose, A. C. Rovero, M. Schroedter, G. H. Sembroski, G. Demet Senturk, A. W. Smith, D. Steele, S. P. Swordy, M. Theiling, S. Thibadeau, A. Varlotta, S. Vincent, R. G. Wagner, S. P. Wakely, J. E. Ward, T. C. Weekes, A. Weinstein, T. Weisgarber, D. A. Williams, S. Wissel, M. Wood, B. Zitzer, Chandra M87 Monitoring, :, D. E. Harris, F. Massaro. 2010-05-03. VERITAS 2008 - 2009 monitoring of the variable gamma-ray source M87. https://doi.org/10.1088/0004-637x%2F716%2F1%2F819

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