The very high energy gamma ray spectra of IES 1959+650 and Mrk 421 as measured with the Whipple 10 m telescope

M. K. Daniel, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, K. Byrum, D. A. Carter-Lewis, O. Celik, P. Cogan, W. Cui, I. De La Calle Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, S. Gammell, K. GibbsG. H. Gillanders, J. Grube, K. J. Guiterrez, J. Hall, D. Hanna, J. Holder, D. Horan, S. Hughes, T. B. Humensky, I. Jung, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. Lloyd-Evans, D. Mendoza, A. Merriman, A. Milovanovic, P. Moriarty, T. Nagai, R. A. Ong, R. Pallassini, J. Perkins, D. Petry, M. Pohl, B. Power-Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, L. Valcarcel, V. V. Vassiliev, R. Wagner, S. P. Wakely, G. Walker, T. C. Weekes, R. J. White, J. Zweerink

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations


In observations made with the Whipple 10 m telescope, 1ES 1959+650 (z = 0.048) was caught in a high flaring state in May 2002, concurrent with a high X-ray state, and in June 2002, for which there was no corresponding X-ray flare. The spectra for both of those occasions are well fitted by a power law of differential spectral index ∼ -2.8. The relative stability of the spectral index for those flares argues strongly in favour of a two-component model as to the emission zones for the two radiation regimes. Markarian 421 (z = 0.031) was observed to be in a high flaring state, at levels of ≥ 3 Crab, during March and April 2004. The average spectrum over this time period shows evidence for a cut-off in the spectrum at ∼ 5 TeV, similar to a cut-off seen during an equivalently strong episode of flaring activity in 2001. The continued appearance of this feature indicates a long term stability, either in the physical conditions at the source, or in the intervening medium (such as attenuation on the extra-galactic infra-red background radiation).

Original languageEnglish (US)
Title of host publicationHigh Energy Gamma-Ray Astronomy - 2nd International Symposium on High Energy Gamma-Ray Astronomy
Number of pages6
StatePublished - 2005
EventInternational Symposium on High Energy Gamma-Ray Astronomy - Heidelberg, Germany
Duration: Jul 26 2004Jul 30 2004

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


OtherInternational Symposium on High Energy Gamma-Ray Astronomy


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