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Probing cosmic accelerators through atmospheric calibration and precision very-high-energy gamma-ray spectroscopy

Final Report Summary - PRECISIONGAMMA (Probing cosmic accelerators through atmospheric calibration and precision very-high-energy gamma-ray spectroscopy)

The project aimed at studying cosmic particle accelerators with the ground-based very-high-energy (VHE; 50 GeV < E < 100 TeV) gamma-ray telescopes of the H.E.S.S. Collaboration located in Namibia, in order to probe fundamental particle acceleration processes at energies far beyond those achievable at terrestrial accelerators and in extreme environments such as supernova remnants (SNRs), pulsars (PSRs) and their wind nebulae (PWNe), and the Galactic Centre. The so-called phase II of H.E.S.S. with the recent adding of a fifth, 28 m-large telescope, enables observations of VHE gamma-rays at low energies (between ~30-50 GeV and 150 GeV), previously beyond reach, with an unprecedented sensitivity. Access to this key energy range allows us to search for, in particular, pulsed VHE emission from PSRs (Crab, Vela), and to investigate the evidence for gamma-ray spectral lines from the Galactic Centre and unassociated sources seen by the Fermi-LAT Space telescope. The main project's objective focused on the analysis and interpretation of the data taken with this cutting-edge Cherenkov instrument within a multi-wavelength approach in order to elucidate the underlying mechanisms responsible for gamma-ray production in the cosmos. Another goal was to integrate a monitoring LIDAR system with H.E.S.S.-II to directly calibrate the telescope data using Monte-Carlo simulations of atmospheric air showers based on real-time, measured atmospheric properties. Such an implementation is expected to improve the energy resolution, reduce the spectral bias, and minimize systematic uncertainties.

The work performed since the beginning of the project has been two-fold, with (1) an implication in the host institute's atmospheric monitoring and calibration program, working towards evaluating the archived LIDAR monitoring data, in particular during the first stages of the LIDAR data analysis in order to derive the atmospheric properties, and (2) a strong involvement in the work related to the H.E.S.S. Galactic Plane Survey (HGPS) and source catalogue, from the extensive data analysis, source detection and characterisation, multi-wavelength interpretation, to the coordination and writing of the associated publications, and frequent dissemination. The main results achieved during the project have been (1) the implementation of the first steps of the LIDAR data analysis chain, dealing with the measured LIDAR signal to be translated into exploitable atmospheric extinction profiles in order to further run Monte-Carlo simulations and calculate the H.E.S.S. instrument response functions, and (2) the final version of the H.E.S.S. source catalogue extracted from the ~2500 h-deep Galactic Plane Survey dataset with an unprecedented point-source sensitivity in the inner Galaxy, accounting for the underlying unresolved large-scale emission and thoroughly dealing with the complexity in the source morphologies. The HGPS catalogue contains 79 sources, with many PWNe and PWN candidates, and within which 16 are new discoveries reported for the first time. Thanks to a methodical search for plausible counterparts, more than two-thirds of the VHE sources are associated with at least one astronomical object that could plausibly account for the production of VHE gamma-rays. The central implication of the researcher in bringing this long-term effort to fruition, including the paper writing, and more generally in many other related works, has already led to several important publications and are about to result in a series of H.E.S.S. Legacy publications to be published in the coming months. Several aspects of the research project (reports, links, etc.) can be found at