Maximum Likelihood Compton Polarimetry with the Compton Spectrometer and Imager

TL;DR

This paper demonstrates that applying a maximum likelihood method to Compton polarimetry data significantly improves the minimum detectable polarization (MDP) in real observations, exemplified by GRB 160530A.

Contribution

It introduces a practical implementation of the maximum likelihood approach for non-ideal Compton polarimeters, enhancing polarization sensitivity in astrophysical measurements.

Findings

Maximum likelihood reduces MDP by 20% for GRB 160530A.

Method improves polarization detection sensitivity in real-world scenarios.

Applicable to future gamma-ray polarization measurements.

Abstract

Astrophysical polarization measurements in the soft gamma-ray band are becoming more feasible as detectors with high position and energy resolution are deployed. Previous work has shown that the minimum detectable polarization (MDP) of an ideal Compton polarimeter can be improved by $\sim 21\%$ when an unbinned, maximum likelihood method is used instead of the standard approach of fitting a sinusoid to a histogram of azimuthal scattering angles. Here we outline a procedure for implementing this maximum likelihood approach for real, non-ideal polarimeters. As an example, we use the recent observation of GRB 160530A with the Compton Spectrometer and Imager. We find that the MDP for this observation is reduced by $20\%$ when the maximum likelihood method is used instead of the standard method.