@article{61a212e6c4fe49c8a723f4ea86791ae9,
title = "Very high energy outburst of Markarian 501 in May 2009",
abstract = "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.",
keywords = "BL Lacertae objects: individual: Mrk 501, Gamma rays: galaxies",
author = "\{The VERITAS Collaboration\} and E. Aliu and S. Archambault and A. Archer and T. Arlen and T. Aune and A. Barnacka and B. Behera and M. Beilicke and W. Benbow and K. Berger and R. Bird and M. B{\"o}ttcher and A. Bouvier and M. Buchovecky and Buckley, \{J. H.\} and V. Bugaev and Cardenzana, \{J. V.\} and M. Cerruti and A. Cesarini and X. Chen and L. Ciupik and E. Collins-Hughes and Connolly, \{M. P.\} and W. Cui and J. Dumm and Eisch, \{J. D.\} and A. Falcone and S. Federici and Q. Feng and Finley, \{J. P.\} and H. Fleischhack and P. Fortin and L. Fortson and A. Furniss and N. Galante and D. Gall and Gillanders, \{G. H.\} and S. Griffin and Griffiths, \{S. T.\} and J. Grube and G. Gyuk and M. H{\"u}tten and N. H{\aa}kansson and J. Holder and G. Hughes and Humensky, \{T. B.\} and Johnson, \{C. A.\} and P. Kaaret and P. Kar and N. Kelley-Hoskins and M. Kertzman and Y. Khassen and D. Kieda and M. Krause and H. Krawczynski and F. Krennrich and Lang, \{M. J.\} and Madhavan, \{A. S.\} and G. Maier and S. McArthur and A. McCann and K. Meagher and J. Millis and P. Moriarty and R. Mukherjee and D. Nieto and \{O'Faol{\'a}in De Bhr{\'o}ithe\}, A. and Ong, \{R. A.\} and M. Orr and Otte, \{A. N.\} and D. Pandel and N. Park and V. Pelassa and Perkins, \{J. S.\} and A. Pichel and M. Pohl and A. Popkow and J. Quinn and K. Ragan and Reyes, \{L. C.\} and Reynolds, \{P. T.\} and E. Roache and J. Rousselle and Rovero, \{A. C.\} and Saxon, \{D. B.\} and Sembroski, \{G. H.\} and K. Shahinyan and F. Sheidaei and C. Skole and Smith, \{A. W.\} and D. Staszak and I. Telezhinsky and M. Theiling and Todd, \{N. W.\} and Tucci, \{J. V.\} and J. Tyler and A. Varlotta and Vassiliev, \{V. V.\} and S. Vincent and Wakely, \{S. P.\} and Weiner, \{O. M.\} and A. Weinstein and R. Welsing and A. Wilhelm and Williams, \{D. A.\} and B. Zitzer and Baring, \{M. G.\} and \{Becerra G{\'o}nzalez\}, J. and Cillis, \{A. N.\} and D. Horan and D. Paneque",
note = "Publisher Copyright: {\textcopyright} 2016 ESO.",
year = "2016",
month = oct,
day = "1",
doi = "10.1051/0004-6361/201628744",
language = "English",
volume = "594",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
}