Reference: E. Aliu et al. (The VERITAS Collaboration), Astronomy & Astrophysics 594: A76, 2016
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Contact: Ana Pichel
The very high energy (VHE; E > 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 54938--54956), 2009, as part of an extensive multi-wavelength campaign from radio to VHE. Strong VHE γ-ray activity was detected on May 1st with Whipple and VERITAS, when the flux (E > 400 GeV) increased to 10 times the pre-flare baseline flux (3.9×10−11 ph cm−2 s−1), reaching five times the flux of the Crab Nebula. This coincided with a decrease in the optical polarization and a rotation of the polarization angle by 15 ∘. This VHE flare showed a fast flux variation with an increase of a factor ∼4 in 25 minutes, and a falling time of ∼50 minutes. We present the observations of the quiescent state previous to the flare and of the high state after the flare, focusing on the flux and spectral variability from Whipple, VERITAS, Fermi-LAT, RXTE, and Swift combined with optical and radio data.
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