A weighted analysis to improve the X-ray polarization sensitivity of IXPE

TL;DR

This paper introduces a weighted analysis method for IXPE's gas pixel detectors, enhancing X-ray polarization sensitivity by selecting and weighting photoelectron tracks based on their shape properties, leading to improved data accuracy.

Contribution

The paper proposes a novel weighting scheme based on track shape properties to improve IXPE's polarization measurement sensitivity, establishing a new baseline for data analysis.

Findings

Significant sensitivity improvement with weighted track analysis

Identification of the best track property for weighting

Baseline implementation for IXPE data processing

Abstract

IXPE is a Small Explorer mission that was launched at the end of 2021 to measure the polarization of X-ray emission from tens of astronomical sources. Its focal plane detectors are based on the Gas Pixel Detector, which measures the polarization by imaging photoelectron tracks in a gas mixture and reconstructing their initial directions. The quality of the single track, and then the capability of correctly determining the original direction of the photoelectron, depends on many factors, e.g., whether the photoelectron is emitted at low or high inclination with respect to the collection plane or the occurrence of a large Coulomb scattering close to the generation point. The reconstruction algorithm used by IXPE to obtain the photoelectron emission direction, also calculates several properties of the shape of the tracks which characterize the process. In this paper we compare several such properties and identify the best one to weight each track on the basis of the reconstruction accuracy. We demonstrate that significant improvement in sensitivity can be achieved with this approach and for this reason it will be the baseline for IXPE data analysis.