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Descrição
The discovery by the Pierre Auger Collaboration of a dipolar anisotropy in the arrival directions of UHECRs with energies exceeding 8 EeV - pointing approximately 120$^\circ$ away from the Galactic center- provides evidence that the majority of UHECR sources are located outside the Milky Way. In light of this, the interpretation of data considering different astrophysical scenarios is essential to tackle modeling of UHECR sources and extragalactic propagation.
The Pierre Auger Collaboration developed a combined fit of both energy spectrum and mass composition data to investigate the constraints imposed by these measurements on the characteristics of potential sources.
Since the energy spectrum and the mass composition are affected by the interactions of the particles with photon fields as they travel extragalactic distances, the energy losses due to the interaction with the Extragalactic Background Light (EBL) must be taken into account once it constitutes the second-most energetic diffuse background, following the cosmic microwave background.
We carried out an analysis considering the extreme EBL models Stecker upper and Stecker lower and their impact on the combined fit of the energy spectrum and composition results for different parameters of evolution of the emissivity of the sources.
We found that differences between best fit parameters are small for the extreme EBL models except for the evolution parameter m < −2. Additionally, our results show a transition from negative values of spectral index to positive ones at m > −2 when the Stecker Lower model is considered while the results presents only negative values for spectral index when the EBL Stecker Upper model is taken into account.
