# Using Muon Rings for the Optical Throughput Calibration of the Cherenkov Telescope Array

## TL;DR

This paper evaluates the use of muon ring images observed by Cherenkov telescopes for calibrating optical throughput and monitoring the optical point spread function, identifying systematic effects and proposing modifications for the CTA.

## Contribution

It demonstrates the feasibility of using muon rings as a primary calibration method for CTA, accounting for systematic effects and suggesting hardware and analysis improvements.

## Key findings

- Muon rings can calibrate optical throughput with high accuracy.
- Systematic effects must be addressed for reliable calibration.
- Muon rings also offer potential for camera pixel flat-fielding.

## Abstract

Muon ring images observed with Imaging Atmospheric Cherenkov Telescopes (IACTs) provide a powerful means to calibrate the optical throughput of IACTs and monitor their optical point spread function. We investigate whether muons ring images can be used as the primary optical throughput calibration method for the telescopes of the future Cherenkov Telescope Array (CTA) and find several additional systematic effects in comparison to previous works. To ensure that the method achieves the accuracy required by CTA, these systematic effects need to be taken into account and minor modifications to the hardware and analysis are necessary. We derive analytic estimates for the expected muon data rates to be used for optical throughput calibration, monitoring of the optical point spread function, with achievable statistical and systematic uncertainties, and explore the potential of muon ring images as a secondary method of camera pixel flat-fielding.