A crosstalk and non-uniformity correction method for the Compact Space-borne Compton Polarimeter POLAR

Abstract

In spite of extensive observations and numerous theoretical studies in the past decades several key questions related with Gamma-Ray Bursts (GRB) emission mechanisms are still to be answered. Precise detection of the GRB polarization carried out by dedicated instruments can provide new data and be an ultimate tool to unveil their real nature. A novel space-borne Compton polarimeter POLAR onboard the Chinese space station TG2 is designed to measure linear polarization of gamma-rays arriving from GRB prompt emissions. POLAR uses plastics scintillator bars (PS) as gamma-ray detectors and multi-anode photomultipliers (MAPMTs) for readout of the scintillation light. Inherent properties of such detection systems are crosstalk and non-uniformity. The crosstalk smears recorded energy over multiple channels making both non-uniformity corrections and energy calibration more difficult. Rigorous extraction of polarization observable requires to take such effects properly into account. We studied influence of the crosstalk on energy depositions during laboratory measurements with X-ray beams. A relation between genuine and recorded energy was deduced using an introduced model of data analysis. It postulates that both the crosstalk and non-uniformities can be described with a single matrix obtained in calibrations with mono-energetic X- and gamma-rays. Necessary corrections are introduced using matrix based equations allowing for proper evaluation of the measured GRB spectra. Validity of the method was established during dedicated experimental tests. The same approach can be also applied in space utilizing POLAR internal calibration sources. The introduced model is general and with some adjustments well suitable for data analysis from other MAPMT-based instruments.

References in corpus (7)

• Short-Duration Gamma-Ray Bursts
• POLAR, a compact detector for Gamma Ray Bursts photon polarization measurements
• Polarization in the prompt emission of gamma-ray bursts and their afterglows
• Calibration of the Gamma-RAy Polarimeter Experiment (GRAPE) at a Polarized Hard X-Ray Beam
• On the operation of X-ray polarimeters with a large field of view
• The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter
• POET: POlarimeters for Energetic Transients

Cited by in corpus (8)

• High Energy Polarimetry of Prompt GRB Emission
• Instrument Performance and Simulation Verification of the POLAR Detector
• In-Orbit Instrument Performance Study and Calibration for POLAR Polarization Measurements
• Gamma-ray burst polarization reduction induced by the Lorentz invariance violation
• In-flight energy calibration of the space-borne Compton polarimeter POLAR
• Response of the first POLAR-2 Prototype to Polarized Beams
• Calibration of Gamma-ray Burst Polarimeter POLAR
• A fully autonomous data center for the space-borne hard X-ray Compton polarimeter POLAR developed at PSI