Related papers: Was the Highest Energy Cosmic Ray a Photon?
The fluorescence technique has been successfully used to detect ultrahigh energy cosmic rays by indirect measurements. The underlying idea is that the number of charged particles in the atmospheric shower, i.e, its longitudinal profile, can…
One of the most fascinating puzzles in particle astrophysics today is that of the origin and nature of the highest energy cosmic rays. The Pierre Auger Observatory (PAO), currently under construction in Province of Mendoza, Argentina, and…
The origin and nature of ultra high energy cosmic rays remains being a mystery. However, great progress has been made in recent years due to the observations performed by the Pierre Auger Observatory and Telescope Array. In particular, it…
We describe a method to analyse inclined air showers produced by ultra high energy cosmic rays using an analytical description of the muon densities. We report the results obtained using data from inclined events…
The recent results of the Pierre Auger Observatory on the possible correlation of Ultra High Energy Cosmic Rays events and several nearby discrete sources could be the starting point of a new era with charged particles astronomy. In this…
Ultra-high-energy cosmic rays (UHECRs) are atomic nuclei from space with vastly higher energies than any other particles ever observed. Their origin and chemical composition remain a mystery. As we show here, the large- and…
Over the last decade a number of important observational results have been reported using data from the Pierre Auger Observatory. We shall review some of the recent key findings that have significantly advanced our understanding of…
The origins of ultra-high energy cosmic rays (UHECRs) remain an open question. Several attempts have been made to cross-correlate the arrival directions of the UHECRs with catalogs of potential sources, but no definite conclusion has been…
The origin of the ultra high energy cosmic rays (UHECRs, $E>10^{18}$ eV) is still uncertain. However, great progress has been achieved due to the data taken by The Pierre Auger and Telescope Array observatories. The UHECR flux presents two…
The present situation with regard to experimental data on ultra high-energy cosmic rays is briefly reviewed. Whilst detailed knowledge of the shape of the energy spectrum is still lacking, it is clear that events above 10^20 eV do exist.…
The composition of ultra-high energy (UHE) cosmic rays E>10^17 eV is still unknown. The observation of UHE photons would extend the observed electromagnetic spectrum to highest energy and open a new channel for multimessenger observations…
The Pierre Auger Observatory has driven the field of ultra-high-energy cosmic ray (UHECR) physics, producing several groundbreaking observations over the last 20 years. One of the most striking findings has been the complex evolution of…
The latest observations of extensive air showers (EAS) induced by ultra-high-energy cosmic rays (UHECR) appear to indicate, prima facie, a transition to heavy primaries at the highest energies. However, this interpretation, which is based…
Based on observations of the depth of shower maximum performed with the hybrid detector of the Auger Observatory, an upper limit on the cosmic-ray photon fraction of 26% (at 95% confidence level) is derived for primary energies above 10^19…
The origin of ultra-high energy (UHE) cosmic rays is still an open question. In the present work, we searched the possible UHE cosmic ray sources using the MAGIC telescope for the associated very high energy (VHE) gamma ray emission. Due to…
The highest energy cosmic ray event reported by the Auger Observatory has an energy of 148 EeV. It does not correlate with any nearby (z$<$0.024) object capable of originating such a high energy event. Intrigued by the fact that the highest…
We have measured the cosmic ray spectrum above 10^17.2 eV using the two air fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, photo-tube and atmospheric calibrations,…
The Southern part of the Pierre Auger Observatory is nearing completion, and has been in stable operation since January 2004 while it has grown in size. The large sample of data collected so far has led to a significant improvement in the…
Cosmic-ray photons above 10^19 eV can convert in the geomagnetic field and initiate a preshower, i.e. a particle cascade before entering the atmosphere. We compare the preshower characteristics at the southern and northern sites of the…
Ultra-high energy photons (UHE, E > 10^19 eV) are inevitably produced during the propagation of 10^20 eV protons in extragalactic space. Their short interaction lengths (<20 Mpc) at these energies, combined with the impressive sensitivity…