Gain factor and parameter settings optimization of the new gamma-ray burst polarimeter POLAR

TL;DR

This paper details the gain optimization, calibration, and testing of the POLAR gamma-ray burst polarimeter, focusing on gain dependence, performance metrics, and response uniformity to enhance its accuracy in space-based X-ray polarization measurements.

Contribution

It introduces a comprehensive gain optimization process and calibration procedures for POLAR, including laboratory and environmental testing results, to improve instrument performance.

Findings

Gain dependence on high voltage for all channels characterized

Instrument's dynamic range and energy resolution detailed

Response non-uniformity and temperature effects analyzed

Abstract

As a space-borne detector POLAR is designed to conduct hard X-ray polarization measurements of gamma-ray bursts on the statistically significant sample of events and with an unprecedented accuracy. During its development phase a number of tests, calibrations runs and verification measurements were carried out in order to validate instrument functionality and optimize operational parameters. In this article we present results on gain optimization togeter with verification data obtained in the course of broad laboratory and environmental tests. In particular we focus on exposures to the $^{137}$Cs radioactive source and determination of the gain dependence on the high voltage for all 1600 detection channels of the polarimeter. Performance of the instrument is described in detail with respect to the dynamic range, energy resolution and temperature dependence. Gain optimization algorithms and response non-uniformity studies are also broadly discussed. Results presented below constitute important parts for development of the POLAR calibration and operation database.