Calibration of the Cherenkov Telescope Array using Cosmic Ray Electrons

TL;DR

Cosmic ray electrons can be used to calibrate the energy scale and efficiency of Cherenkov telescopes like CTA with high precision, reducing reliance on atmospheric models and enabling independent verification.

Contribution

This study demonstrates the potential of cosmic ray electrons as a calibration tool for next-generation Cherenkov telescopes, achieving sub-3% energy scale accuracy.

Findings

Collection efficiency variations corrected to better than 1%

Electron spectrum break at ~0.9 TeV calibrates energy scale to 3%

Statistical errors negligible below a few TeV for hours-long observations

Abstract

Cosmic ray electrons represent a background for gamma-ray observations with Cherenkov telescopes, initiating air-showers which are difficult to distinguish from photon-initiated showers. This similarity, however, and the presence of cosmic ray electrons in every field observed, makes them potentially very useful for calibration purposes. Here we study the precision with which the relative energy scale and collection area/efficiency for photons can be established using electrons for a major next generation instrument such as CTA. We find that variations in collection efficiency on hour timescales can be corrected to better than 1%. Furthermore, the break in the electron spectrum at ~0.9 TeV can be used to calibrate the energy scale at the 3% level on the same timescale. For observations on the order of hours, statistical errors become negligible below a few TeV and allow for an energy scale cross-check with instruments such as CALET and AMS. Cosmic ray electrons therefore provide a powerful calibration tool, either as an alternative to intensive atmospheric monitoring and modelling efforts, or for independent verification of such procedures.