Observation of Markarian 421 in TeV gamma rays over a 14-year time span

V. A. Acciari, T. Arlen, T. Aune, W. Benbow, R. Bird, A. Bouvier, S. M. Bradbury, J. H. Buckley, V. Bugaev, I. De La Calle Perez, D. A. Carter-Lewis, A. Cesarini, L. Ciupik, E. Collins-Hughes, M. P. Connolly, W. Cui, C. Duke, J. Dumm, A. Falcone, S. FedericiD. J. Fegan, S. J. Fegan, J. P. Finley, G. Finnegan, L. Fortson, J. Gaidos, N. Galante, D. Gall, K. Gibbs, G. H. Gillanders, S. Griffin, J. Grube, G. Gyuk, D. Hanna, D. Horan, T. B. Humensky, P. Kaaret, M. Kertzman, Y. Khassen, D. Kieda, H. Krawczynski, F. Krennrich, M. J. Lang, J. E. McEnery, A. S. Madhavan, P. Moriarty, T. Nelson, A. O'Faoláin De Bhróithe, R. A. Ong, M. Orr, A. N. Otte, J. S. Perkins, D. Petry, A. Pichel, M. Pohl, J. Quinn, K. Ragan, T. Reynolds, E. Roache, A. Rovero, M. Schroedter, G. H. Sembroski, A. Smith, I. Telezhinsky, M. Theiling, J. Toner, J. Tyler, A. Varlotta, M. Vivier, S. P. Wakely, J. E. Ward, T. C. Weekes, A. Weinstein, R. Welsing, D. A. Williams, S. Wissel

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45 Scopus citations


The variability of the blazar Markarian 421 in TeV gamma rays over a 14-year time period has been explored with the Whipple 10 m telescope. It is shown that the dynamic range of its flux variations is large and similar to that in X-rays. A correlation between the X-ray and TeV energy bands is observed during some bright flares and when the complete data sets are binned on long timescales. The main database consists of 878.4 h of observation with the Whipple telescope, spread over 783 nights. The peak energy response of the telescope was 400 GeV with 20% uncertainty. This is the largest database of any TeV-emitting active galactic nucleus (AGN) and hence was used to explore the variability profile of Markarian 421. The time-averaged flux from Markarian 421 over this period was 0.446±0.008 Crab flux units. The flux exceeded 10 Crab flux units on three separate occasions. For the 2000-2001 season the average flux reached 1.86 Crab units, while in the 1996-1997 season the average flux was only 0.23 Crab units.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalAstroparticle Physics
StatePublished - Feb 2014

Bibliographical note

Funding Information:
This research is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, by NSERC in Canada, by Science Foundation Ireland (SFI 10/RFP/AST2748) and by STFC in the U.K. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instruments.


  • AGN
  • Markarian 421
  • TeV gamma rays


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