“An upper limit to the photon fraction in cosmic rays above 1019 eV from the Pierre Auger Observatory,”

THE PIERRE AUGER COLLABORATION, A. TAMASHIRO

ASTROPARTICLE PHYSICS

Elsevier

Año: 2007 vol. 27 p. 155 - 168

0927-6505

   An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmicrays with energies greater than 10^19 eV, based on observations of the depth of showermaximum performed with the hybrid detector of the Pierre Auger Observatory. Thisis the first such limit on photons obtained by observing the fluorescence light profileof air showers. This upper limit confirms and improves on previous results fromthe Haverah Park and AGASA surface arrays. Additional data recorded with theAuger surface detectors for a subset of the event sample support the conclusion thata photon origin of the observed events is not favored.