Advancements in the Calibration of the FlashCam Camera for Imaging Air Cherenkov Telescopes and a New Analysis of HESS J1729-345

Abstract

FlashCam (FC) is a novel camera design for imaging air Cherenkov telescopes (IACTs). FC is designated to be used in the Medium-Sized Telescopes (MSTs) of the southern array of the upcoming Cherenkov Telescope Array (CTA). In 2019, a fully functional advanced prototype of an FC camera was installed into the 28m CT5 telescope of the High Energetic Stereoscopic System (H.E.S.S.). This thesis covers several topics related to the calibration of FC, both for the existing camera within H.E.S.S., and for future installations of the camera in CTA. An LED-based pulse emitter, currently used for flatfield measurements in H.E.S.S., is characterized to investigate its suitability as an on-site calibration unit for FC in CTA South. Such a calibration unit should ideally be able to homogeneously illuminate the camera over the full dynamic range of FC, which goes beyond the design requirements of the current device. Laboratory measurements and simulations of the camera's response to the light pulses show that the current device cannot handle the needs of FC in an MST. The updated requirements for a calibration unit are derived from these investigations. Following the installation of FC into CT5, the Monte-Carlo (MC) simulation chain of H.E.S.S. had to be validated. MC simulations are critical to the analysis of IACT data, so the simulation configuration must match the actual conditions. This thesis' author was part of a small team that validated the simulations for the HAP analysis chain of H.E.S.S. The work of this team led to a significant improvement in the reconstruction of the energy flux of astronomical sources. Here, the MC validation process is presented step by step, with the author's contributions highlighted. With the validated analysis configuration in hand, a pending step in the FC science verification could be addressed. The example of the supernova remnant HESS J1731-347 demonstrates the ability of the FC-equipped CT5 to correctly reconstruct the key parameters of a moderately extended source. The analysis of HESS J1731-347 triggered a study into the energy dependence of the neighboring source HESS J1729-345, using archival data from the CT1-4 telescopes of H.E.S.S. The main result of this study is that HESS J1729-345 actually consists of two spatially separated sources. One is only detected significantly at energies below 1TeV, and is spatially aligned with a possible star-forming region more than 1 kpc away from HESS J1731-347. The other is fainter and is only detected significantly above 1TeV. This second source is spatially coincident with a molecular cloud that is suspected to interact with escaping particles from HESS J1731-347, a hypothesis supported by the results of this work.