Design and performance of the angle integrating Cerenkov array AIROBICC

An air-shower array consisting of 49 open huts with photomultiplier tubes viewing the night sky over a solid angle of about 1 steradian is described. The array is operating in conjunction with the HEGRA installation. The main objectives of the experiment are VHE to UHE #gamma#-ray astronomy and a determination of the chemical composition of cosmic rays. The design principles, construction and performance in angular resolution, energy threshold and determination of shower parameters are discussed. (orig.)SIGLEAvailable from TIB Hannover: RR 2916(94-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Methods to determine the angular resolution of the HEGRA extended air shower scintillator array

A precise knowledge of the angular resolution of scintiallator arrays used to observe extended air showers (EAS) is of key importance in the search for VHE/UHE #gamma# point sources. Four independent methods have been used to determine the mean resolution for which a value of <#DELTA##THETA#_6_3> of 0.8 (1.0 ) at a proton threshold of 50 (40) TeV has been found for the HEGRA EAS-array. (orig.)SIGLEAvailable from TIB Hannover: RR 2916(95-25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

A search for gamma radiation above 24 TeV energy from cosmic point sources

The HEGRA collaboration has searched for #gamma#-ray emission from 36 potential cosmic point sources with the wide angle air Cerenkov detector AIROBICC which is part of the HEGRA cosmic ray detector complex of La Palma. AIROBICC has a #gamma#-ray energy threshold of around 24 TeV and a mean angular resolution of 0.29 . None of the sources could be found. Upper limits to their fluxes are given. For the VHE #gamma# ray emitters, the Crab nebula and Mrk 421, these flux limits are below those extrapolated from lower energy observations. Our lower limit for Mrk 421 might be interpreted either as being due to an energy cut-off in the acceleration mechanism or to the onset of #gamma#-interaction with photons of the universal infrared background. (orig.)31 refs.SIGLEAvailable from TIB Hannover: RR 2916(95-01) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Search for isotropic #gamma# radiation of cosmological origin between 65 and 200 TeV

Electromagnetic energy injected into the universe above a few hundred TeV is expected to pile up as #gamma# radiation in the energy range between about 65 and 100 TeV due to its interaction with the 2.7 K background radiation. We present an upper limit (90% C.L.) on the ratio of primary #gamma# to charged cosmic rays in the energy interval 65-160 TeV (80-200 TeV) of 10.3.10"3 (7.8.10"-"3). Data from the HEGRA cosmic-ray detector complex consisting of a wide angle Cerenkov array (AIROBICC) measuring the lateral distribution of air Cerenkov light and a scintillator array, were used with a novel method to discriminate #gamma#-ray and hadron induced air showers. If the presently unmeasured universal far infrared background radiation is not too intense, the result rules out a topological-defect origin of ultrahigh energy cosmic rays for masses of the X particle released by the defects equal to or larger than about 10"1"6 GeV. (orig.)Available from TIB Hannover: RR 2916(94-28) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman