Sensitivity Improvements of Very-High-Energy γ-Ray Detection with the Upgraded HESS I Cameras using Full Waveform Processing

The High Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes in Namibia observing gamma-rays in the energy range from a few tens of GeV to a few tens of TeV. The Cherenkov signal detected by photomultiplier tubes is sampled at 1 GHz. In nominal data acquisition (charge) mode, this signal is integrated over a fixed window of 16 ns in case trigger conditions are met. Thanks to the electronics upgrade of the four H.E.S.S. I cameras in spring 2017, full 1 GHz-sampled waveforms can be read out in parallel to the nominal charge mode. This allows for a higher flexibility in data analysis like signal integration along the signal time gradient, thereby increasing the signal-to-noise ratio and thus the sensitivity at the lower end of the energy range. Furthermore, it prevents the truncation of Cherenkov events lasting longer than 16 ns, enhancing the shower reconstruction of gamma-ray events with TeV energies and high impact distances. Observations of PeVatron candidates may profit a lot from this new data acquisition mode since precise reconstruction of the rare multi-TeV gamma-ray events is improved - a crucial aspect to investigate a potential spectral cut-off. Performance studies of the upgraded H.E.S.S. I cameras with a focus on sample mode data analysis and comparison to nominal charge mode data are presented in this contribution.