Flasher and muon-based calibration of the GCT telescopes proposed for the Cherenkov Telescope Array

TL;DR

This paper discusses calibration methods for the GCT telescopes in the Cherenkov Telescope Array, focusing on LED flashers and muon ring techniques to ensure accurate camera performance and optical throughput measurement.

Contribution

It introduces the design and performance of LED-based flashers for GCT calibration and explores muon rings as an end-to-end optical calibration method.

Findings

Flasher units effectively calibrate camera flat-fielding and linearity.

Muon ring analysis shows promise for end-to-end optical throughput calibration.

Performance of flashers supports precise calibration scenarios.

Abstract

The GCT is a dual-mirror Small-Sized-Telescope prototype proposed for the Cherenkov Telescope Array. Calibration of the GCT's camera is primarily achieved with LED-based flasher units capable of producing $\sim4$ ns FWHM pulses of 400 nm light across a large dynamic range, from 0.1 up to 1000 photoelectrons. The flasher units are housed in the four corners of the camera's focal plane and illuminate it via reflection from the secondary mirror. These flasher units are adaptable to allow several calibration scenarios to be accomplished: camera flat-fielding, linearity measurements (up to and past saturation), and gain estimates from both single pe measurements and from the photon statistics at various high illumination levels. In these proceedings, the performance of the GCT flashers is described, together with ongoing simulation work to quantify the efficiency of using muon rings as an end-to-end calibration for the optical throughput of the GCT.