Search

The origin and nature of the ultrahigh energy cosmic rays remains a mystery. However, considerable progress has been achieved in past years due to observations performed by the Pierre Auger Observatory and Telescope Array. Above $10^{18}$ eV the observed energy spectrum presents two features: a hardening of the slope at $\sim 10^{18.6}$ eV, which is known as the ankle, and a suppression at $\sim 10^{19.6}$ eV. The composition inferred from the experimental data, interpreted by using the current high energy hadronic interaction models, seems to be light below the ankle, showing a trend to heavier nuclei for increasing values of the primary energy. Also, the anisotropy information is consistent with an extragalactic origin of this light component that would dominate the spectrum below the ankle. Therefore, the models that explain the ankle as the transition from the galactic and extragalactic components are disfavored by present data. Recently, it has been proposed that this light component originates from the photodisintegration of more energetic and heavier nuclei in the source environment. The formation of the ankle can also be explained by this mechanism. In this work we study in detail this general scenario but in the context of the central region of active galaxies. In this case, the cosmic rays are accelerated near the supermassive black hole present in the central region of these types of galaxies, and the photodisintegration of heavy nuclei takes place in the radiation field that surrounds the supermassive black hole., Accepted for publication in PRD

The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory (Tibet, 4300 m a.s.l., 606 g/cm2) has an high segmentation that allows the detection of air showers with greater detail and lower energy threshold (a few hundred GeV) compared to other EAS arrays. The spectrum of the primary cosmic ray light (p+He) component in the energy range ∼ 10 – 100 TeV is measured selecting quasi-vertical showers ( θ 15 ° ) with the reconstructed core position located in a 40×40 m2 fiducial area. The results are compared with other measurements carried out with direct methods.