In-Orbit Instrument Performance Study and Calibration for POLAR Polarization Measurements

TL;DR

This paper presents a comprehensive in-orbit performance analysis and calibration of the POLAR detector, crucial for accurate gamma-ray burst polarization measurements, including calibration procedures, error analysis, and systematic uncertainty estimation.

Contribution

It provides detailed calibration and performance assessment of POLAR in orbit, enhancing the reliability of polarization data analysis for transient gamma-ray sources.

Findings

Calibration parameters such as noise, gain, and crosstalk were quantified.

Temperature effects on detector performance were characterized.

Systematic errors in polarization measurements were estimated through simulations.

Abstract

POLAR is a compact space-borne detector designed to perform reliable measurements of the polarization for transient sources like Gamma-Ray Bursts in the energy range 50-500keV. The instrument works based on the Compton Scattering principle with the plastic scintillators as the main detection material along with the multi-anode photomultiplier tube. POLAR has been launched successfully onboard the Chinese space laboratory TG-2 on 15th September, 2016. In order to reliably reconstruct the polarization information a highly detailed understanding of the instrument is required for both data analysis and Monte Carlo studies. For this purpose a full study of the in-orbit performance was performed in order to obtain the instrument calibration parameters such as noise, pedestal, gain nonlinearity of the electronics, threshold, crosstalk and gain, as well as the effect of temperature on the above parameters. Furthermore the relationship between gain and high voltage of the multi-anode photomultiplier tube has been studied and the errors on all measurement values are presented. Finally the typical systematic error on polarization measurements of Gamma-Ray Bursts due to the measurement error of the calibration parameters are estimated using Monte Carlo simulations.