Refine
Has Fulltext
- no (11)
Year of publication
- 2012 (11) (remove)
Document Type
- Article (11)
Language
- English (11)
Is part of the Bibliography
- yes (11)
Keywords
- gamma rays: galaxies (5)
- BL Lacertae objects: general (1)
- BL Lacertae objects: individual (1ES 0414+009, ERJ0416+011) (1)
- BL Lacertae objects: individual (RBS 0413-VER J0319+187) (1)
- cosmic rays (1)
- dark matter (1)
- galaxies: active (1)
- galaxies: clusters: general (1)
- galaxies: clusters: individual (Coma (ACO 1656)) (1)
- galaxies: individual (M 87) (1)
VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +/- 0.16) x 10(-11) cm(-2) s(-1) at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 +/- 0.68) x 10(-11) cm(-2) s(-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(-0.15)(+0.22) days. The shortest detected exponential rise time is three times as long, at 2.87(+1.65)(-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.