A Measurement of the UHECR Spectrum with the HiRes FADC Detector

We have measured the energy spectrum of ultra-high energy cosmic rays (UHECR) with the HiRes FADC detector (HiRes-2) in monocular mode. A detailed Monte Carlo simulation of the detector response to air showers has been used to calculate the energy dependent acceptance of the air fluorescence detector. The measured spectrum complements the measurement by the HiRes-1 detector down to lower energies. Systematic effects of the assumed input spectrum and composition on the aperture are presented, as well as systematics due to the atmosphere.