Study of the calibration method using the stars measured by the EUSO-TA telescope

TL;DR

This paper presents a calibration method for the EUSO-TA telescope using star measurements, enabling precise detector pointing and absolute calibration, which is crucial for accurate cosmic ray observations in space-borne missions.

Contribution

The paper introduces a star-based calibration technique for EUSO fluorescence detectors, improving pointing accuracy and detector calibration methods.

Findings

Star signals help determine detector pointing accuracy.

Method provides information on the point spread function.

Calibration method applicable to space-borne EUSO missions.

Abstract

EUSO-TA is a ground-based experiment, placed at Black Rock Mesa of the Telescope Array site as a part of the JEM-EUSO (Joint Experiment Missions for the Extreme Universe Space Observatory) program. The UV fluorescence imaging telescope with a field of view of about 10.6 deg x 10.6 deg consisting of 2304 pixels (36 Multi-Anode Photomultipliers, 64 pixels each) works with 2.5-microsecond time resolution. An experimental setup with two Fresnel lenses allows for measurements of Ultra High Energy Cosmic Rays in parallel with the TA experiment as well as the other sources like flashes of lightning, artificial signals from UV calibration lasers, meteors and stars. Stars increase counts on pixels while crossing the field of view as the point-like sources. In this work, we discuss the method for calibration of EUSO fluorescence detectors based on signals from stars registered by the EUSO-TA experiment during several campaigns. As the star position is known, the analysis of signals gives an opportunity to determine the pointing accuracy of the detector. This can be applied to space-borne or balloon-borne EUSO missions. We describe in details the method of the analysis which provides information about detector parameters like the shape of the point spread function and is the way to perform absolute calibration of EUSO cameras.