Geometry and optics calibration of WFCTA prototype telescopes using star light

TL;DR

This paper details the calibration of WFCTA prototype telescopes using star light to improve pointing accuracy and optical property measurements, essential for cosmic ray and gamma-ray observations in the LHAASO project.

Contribution

It introduces a calibration method using UV bright stars to enhance telescope pointing accuracy and optical characterization for the WFCTA prototypes.

Findings

Improved pointing accuracy of the telescopes.

Quantified optical properties and spot size.

Identified unrecorded photon fractions in camera areas.

Abstract

The Large High Altitude Air Shower Observatory project is proposed to study high energy gamma ray astronomy ( 40 GeV-1 PeV ) and cosmic ray physics ( 20 TeV-1 EeV ). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study energy spectrum and compositions of cosmic ray by measuring the total Cherenkov light generated by air showers and shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial to the direction reconstruction of the primary particles. On the other hand the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera.