2003/05/19 by Daniel De Marco, De Marco, Daniel, Pasquale Blasi +3
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0305336
4 pages. To be published in the Proceedings of the 28th International Cosmic Ray Conference
arxiv created 2003/05/19 · arxiv updated 2009/12/01
We developed a numerical simulation of the propagation of UHECR in the Cosmic Microwave Background (CMB) and we used it to determine the significance of the GZK feature in the spectrum of UHECR measured by AGASA and HiRes. We find that these two experiments are best fit by two different injection spectra in the region below 1020 eV and that the error bars around the GZK feature are dominated by fluctuations which leave a determination of the GZK feature not attainable at present. In addition the comparison of the spectra of AGASA and HiRes suggests the presence of about a 30% systematic errors in the relative energy determination of the two experiments. Correcting for these systematics, the two experiments are brought in agreement at energies below 1020 eV and, in this region, are best fit by an injection spectrum with spectral index 2.5-2.6. In the high energy region (above 1020 eV) the two experiments maintain their disagreement, but only at the 2sigma level. Our results clearly show the need for much larger experiments such as Auger, EUSO, and OWL, that can increase the number of detected events by one or two orders of magnitude.