Upper limit on the ultrahigh-energy photon flux from AGASA and Yakutsk data
Abstract
We present the interpretation of the muon and scintillation signals of ultrahigh-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest-energy events with known muon content and conclude that at the 95% confidence level none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at a 95% confidence level on the fraction of primary photons in the cosmic-ray flux above 1020eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the Greisen-Zatsepin-Kuzmin cutoff problem.
- Publication:
-
Physical Review D
- Pub Date:
- March 2006
- DOI:
- 10.1103/PhysRevD.73.063009
- arXiv:
- arXiv:astro-ph/0601449
- Bibcode:
- 2006PhRvD..73f3009R
- Keywords:
-
- 98.70.Sa;
- 96.50.sd;
- Cosmic rays;
- Extensive air showers;
- Astrophysics
- E-Print:
- revtex, 8 pages, 4 figures