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

During 1997, the BL Lac Object Mkn 501 was the brightest known object in th e TeV gamma-ray sky. The emission was characterized by dramatic Variations in intensity with a mean flux exceeding by a factor of three the steady gam ma-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 0.1 degrees, an energy resolution of 20%, and a flux sensitivity nu F-nu at 1 TeV of 10(-11) ergs/cm(2)sec similar or equal to 1/4 Crab for 1 hour of observation time (S/root B=5 sigma), has been us ed in 1997 for a comprehensive study of the spectral and temporal character istics of the TeV gamma-ray emission from Mkn 501 on time scales of several hours or less. In this paper (Part I) the gamma-ray fluxes and spectra on a diurnal basis during the period March to October 1997 are presented. Furt hermore, 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. Fina lly the implications of these results on the physics of relativistic jets i n BL Lac objects are briefly discussed. The companion paper (Part II) descr ibes the results from the stand alone telescopes CT1 and CT2.