Reference: E. Aliu et al. (The VERITAS Collaboration), Astronomy & Astrophysics 594: A76, 2016

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ArXiv: ArXiV:1608.01569

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 (3.9×1011 ph cm2 s1), 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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