Speaker
Description
The Pierre Auger Observatory has measured the spectrum of ultra-high-energy cosmic rays (UHECRs) with unprecedented precision, as well as the distribution of the depths of the maximum of the shower development in the atmosphere, which provide a reliable estimator of the mass composition. The measurements above 0.7 EeV can be interpreted within a standard model assuming two populations of uniformly distributed sources, one with a soft spectrum dominating the flux below few EeV, and another one with a very hard spectrum dominating above that energy. When considering the presence of intense extragalactic magnetic fields between our Galaxy and the closest sources and a high-energy population with low spatial density, a magnetic horizon appears, depleting the flux of low-energy particles, which could explain the very hard spectrum observed at Earth. The distribution of arrival directions, which at energies above 32 EeV shows indications of a correlation with a population of starburst galaxies or the radio galaxy Cen A are also important to constrain the sources of UHECRs. It is shown that adding a fractional contribution from these sources of about 20% to the homogeneous background leads to an improvement to the model likelihood.
