Determination of the Energy Spectrum of UHECRs using Air Showers Detected by the Fluorescence and Surface Detector of the Pierre Auger Observatory

The origin, propagation and mass composition of ultrahigh-energy cosmic-rays (UHECRs) are still open questions. A precise measurement of the spectral features of the UHECR energy spectrum provides important clues to answer these questions.

In this contribution, we present an analysis of air shower data using a hybrid technique, i.e. the combination of surface (SD) and fluorescence detector (FD) measurements from the Pierre Auger Observatory. The high statistics of hybrid data available after more than 15 years of UHECR observations enable us to evaluate environmental influences on detection capabilities as well as to optimize selection criteria using measured rather than simulated data. We will show how previous estimates of the hybrid spectrum can be improved and present a preliminary calorimetric measurement of the energy spectrum of UHECRs.