Interpretation of Cosmic Ray Composition: The Pathlength Distribution

Abstract

ABSTPACTThe chemical composition of cosmic ray nuc ' Lei with 3<Z<28 between a few hundred MeV/nuc and a few hundred GeV / nuc are compared with a consistent set of propagation calculations. These include the effects of spallation ( energydependent cross sections are used), escape, ionLzation loss in the interstellar medium and deceleration in the solar cavity. The amount of matter traversed by cosmic rays is found to be about 7 g/cm2 , independent of energy between 100 MeV / nuc and 2 GeV/nuc, Above 2 GeV / nuc, the escape length varies as E_0'Gto'1. In addition, a procedure has been developed to measure the shape of the cosmic ray pathlength distribution.Utilizing Oft ratio of Fe-secondaries to Fe y in the cosmic rays,^,presently available data are found to be consistent with tin exponential distribution, and to eliminate models in which the path length distribution is severely truncated. To tie down the shape of the distribution more precisely, new measurements of the cosmic ray composition presently becoming available from experiments on the HEAO-• 3 satellite will have to be coupled with improved measurements of the energy dependence of partial, and total,, cross sections.

Measurement of the radial distribution of Cherenkov light generated by TeV γ-ray air showers

“…The extragalactic VHE γ-ray source Mrk 501 [15,16] showed in 1997 significant activity, with peak flux levels reaching up to 10 times the flux of the Crab nebula (see [17] for a summary of experimental results, first HEGRA results are given in [8]). The telescopes of the HEGRA IACT system were directed towards Mrk 501 for about 140 h, accumulating a total of about 30000 γ-ray events at zenith angles between 10 • and 45 • .…”