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Astron. Astrophys. 342, 69-86 (1999)

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The temporal characteristics of the TeV gamma-radiation from Mkn 501 in 1997

I. Data from the stereoscopic imaging atmospheric Cherenkov telescope system of HEGRA

F.A. Aharonian 1, A.G. Akhperjanian 7, J.A. Barrio 2,3, K. Bernlöhr  *  1, H. Bojahr 6, J.L. Contreras 3, J. Cortina 3, A. Daum 1, T. Deckers 5, V. Fonseca 3, J.C. Gonzalez 3, G. Heinzelmann 4, M. Hemberger 1, G. Hermann  **  1, M. Heß 1, A. Heusler 1, W. Hofmann 1, H. Hohl 6, D. Horns 4, A. Ibarra 3, R. Kankanyan 1,7, O. Kirstein 5, C. Köhler 1, A. Konopelko  ***  1, H. Kornmeyer 2, D. Kranich 2, H. Krawczynski 1,4, H. Lampeitl 1, A. Lindner 4, E. Lorenz 2, N. Magnussen 6, H. Meyer 6, R. Mirzoyan 2, A. Moralejo 3, L. Padilla 3, M. Panter 1, D. Petry  ****  2,6, R. Plaga 2, A. Plyasheshnikov[FORMULA]  1, J. Prahl 4, G. Pühlhofer 1, G. Rauterberg 5, C. Renault 1, W. Rhode 6, V. Sahakian 7, M. Samorski 5, D. Schmele 4, F. Schröder 6, W. Stamm 5, H.J. Völk 1, B. Wiebel-Sooth 6, C. Wiedner 1, M. Willmer 5 and H. Wirth 1

1 Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg, Germany
2 Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München, Germany
3 Universidad Complutense, Facultad de Ciencias Físicas, Ciudad Universitaria, E-28040 Madrid, Spain
4 Universität Hamburg, II. Institut fuer Experimentalphysik, Luruper Chausse 149, D-22761 Hamburg, Germany
5 Universität Kiel, Institut für Kernphysik, Olshausenstrasse 40, D-24118 Kiel, Germany
6 Universität Wuppertal, Fachbereich Physik, Gaußstrasse 20, D-42097 Wuppertal, Germany
7 Yerevan Physics Institute, Alikhanian Br. 2, 375036 Yerevan, Armenia

Received 12 August 1998 / Accepted 21 October 1998


During 1997, the BL Lac Object Mkn 501 was the brightest known object in the TeV [FORMULA]-ray sky. The emission was characterized by dramatic variations in intensity with a mean flux exceeding by a factor of three the steady [FORMULA]-ray flux of the Crab Nebula. The stereoscopic HEGRA system of 4 Imaging Atmospheric Cherenkov Telescopes, with an energy threshold of about 500 GeV, an angular resolution of [FORMULA], an energy resolution of [FORMULA], and a flux sensitivity [FORMULA] at 1 TeV of [FORMULA] [FORMULA] 1/4 Crab for 1 hour of observation time (S/[FORMULA]=5[FORMULA]), has been used in 1997 for a comprehensive study of the spectral and temporal characteristics of the TeV [FORMULA]-ray emission from Mkn 501 on time scales of several hours or less. In this paper (Part I) the [FORMULA]-ray fluxes and spectra on a diurnal basis during the period March to October 1997 are presented. Furthermore, the correlation of the TeV emission with the flux measured by the RXTE All Sky Monitor in the energy range from 2 to 12 keV are studied. Finally the implications of these results on the physics of relativistic jets in BL Lac objects are briefly discussed. The companion paper (Part II) describes the results from the stand alone telescopes CT1 and CT2.

Key words: gamma rays: observations – galaxies: BL Lacertae objects: individual: Mkn 501

* Now at Forschungszentrum Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany
** Now at Enrico Fermi Institute, University of Chicago, 933 East 56th Street, Chicago, IL 60637, USA
*** Permanent address: Altai State University, Dimitrov Street 66, 656099 Barnaul, Russia
**** Now at Universidad Autónoma de Barcelona, Institut de Física d'Altes Energies, E-08193 Bellaterra, Spain

Send offprint requests to: H. Krawczynski (Henric.Krawczynski@mpi-hd.mpg.de)

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998