Speaker
Description
The measurement of the energy spectrum of ultra-high-energy cosmic rays (UHECRs) is an essential step towards understanding their acceleration, propagation and intergalactic origin.
With the Pierre Auger Observatory, it is possible to probe UHECRs with energies up to $10^{20}\,$eV and beyond.
Located in Argentina it comprises more than 1600 water Cherenkov detectors spread over an area of 3000 square kilometers overlooked by Fluorescence detectors.
Starting in 2004 the first phase of the Observatory’s data-taking finished in the end of 2021 accumulating an exposure of about $80 000\,\text{km}^2\text{sr\,yr}$.
In this contribution, we present the measurements of the cosmic-ray energy spectrum from the Phase I data analysis.
The hybrid detector layout of the Pierre Auger Observatory with surface detector arrays of different densities enables the coverage of a wide energy range.
Features observed by other experiments, such as the "second knee" at around $200\,$PeV, the "ankle" at $5\,$EeV and the steepening at $50\,$EeV are highly significant.
Moreover, a new feature has been identified above the "ankle".
Between $2.5\times10^{18}\,$eV and $5\times10^{19}\,$eV the measurement is the most precise made so far as the accumulated exposure is large enough so that the flux measurement is dominated by systematic uncertainties.
Additionally, the combined fit of the measured energy spectrum, shower maximum depth distributions and arrival directions of ultra-high-energy cosmic rays is known to constrain the parameters of astrophysical models and source distributions.
All in all, the Phase I results comprise a major step forward in the understanding of the UHECRs and establish the cornerstone for upcoming Phase II studies with the upgraded AugerPrime detector.
