Very high energy outburst of Markarian 501 in May 2009

E. Aliu, S. Archambault, A. Archer, T. Arlen, T. Aune, A. Barnacka, B. Behera, M. Beilicke, W. Benbow, K. Berger, R. Bird, M. Böttcher, A. Bouvier, M. Buchovecky, J. H. Buckley, V. Bugaev, J. V. Cardenzana, M. Cerruti, A. Cesarini, X. ChenL. Ciupik, E. Collins-Hughes, M. P. Connolly, W. Cui, J. Dumm, J. D. Eisch, A. Falcone, S. Federici, Q. Feng, J. P. Finley, H. Fleischhack, P. Fortin, L. Fortson, A. Furniss, N. Galante, D. Gall, G. H. Gillanders, S. Griffin, S. T. Griffiths, J. Grube, G. Gyuk, M. Hütten, N. Håkansson, J. Holder, G. Hughes, T. B. Humensky, C. A. Johnson, P. Kaaret, P. Kar, N. Kelley-Hoskins, The VERITAS Collaboration

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


The very high energy (VHE; E> 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 54 938-54 956), 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 min, and a falling time of ∼50 min. 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.

Original languageEnglish (US)
Article numberA76
JournalAstronomy and Astrophysics
StatePublished - Oct 1 2016

Bibliographical note

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  • BL Lacertae objects: individual: Mrk 501
  • Gamma rays: galaxies


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