VERITAS OBSERVATIONS OF DAY-SCALE FLARING OF M 87 IN 2010 APRIL

Journal Article · Mon Feb 20 00:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/746/2/141· OSTI ID:22011733

Aliu, E; Errando, M ^[1]; Arlen, T ^[2]; Aune, T; Bouvier, A ^[3]; Beilicke, M; Buckley, J H; Bugaev, V; Dickherber, R ^[4]; Benbow, W ^[5]; Bradbury, S M ^[6]; Byrum, K ^[7]; Cannon, A; Collins-Hughes, E ^[8]; Cesarini, A; Connolly, M P ^[9]; Ciupik, L ^[10]; Cui, W ^[11]; Duke, C ^[12]; Falcone, A ^[13] ; others, and

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1. Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States)
2. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
3. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
4. Department of Physics, Washington University, St. Louis, MO 63130 (United States)
5. Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
6. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
7. Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States)
8. School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)
9. School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
10. Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
11. Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
12. Department of Physics, Grinnell College, Grinnell, IA 50112-1690 (United States)
13. Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)

VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 {+-} 0.16) Multiplication-Sign 10{sup -11} cm{sup -2} s{sup -1} at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 {+-} 0.68) Multiplication-Sign 10{sup -11} cm{sup -2} s{sup -1} for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90{sup +0.22}{sub -0.15} days. The shortest detected exponential rise time is three times as long, at 2.87{sup +1.65}{sub -0.99} days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 {+-} 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

• OSTI ID: 22011733
• Journal Information: Astrophysical Journal, Vol. 746, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC ELECTRONS
FLARING
GAMMA RADIATION
PULSE RISE TIME
RADIO GALAXIES