Hard X-ray Polarimetry -- An overview of the method, science drivers and recent findings

TL;DR

Recent advances in hard X-ray polarimetry have led to new measurements revealing insights into astrophysical phenomena, with ongoing developments promising increased sensitivity and new scientific opportunities.

Contribution

This paper provides an overview of recent findings, discusses the science potential, and reviews technological improvements in hard X-ray polarimetry.

Findings

New polarization measurements from AstroSat, POLAR, GAP, and PoGO+

Insights into black hole coronae, disk-jet connections, and pulsar emission mechanisms

Potential for significant sensitivity improvements with new detector technologies

Abstract

The last decade has seen a leapfrog in the interest in X-ray polarimetry with a number of new polarization measurements in hard X-rays from AstroSat, POLAR, GAP, and PoGO+. The measurements provide some interesting insights into various astrophysical phenomena such as coronal geometry and disk-jet connection in black hole X-ray binaries, hard X-ray emission mechanism in pulsars and Gamma Ray Bursts (GRB). They also highlight an increase in polarization with energy which makes hard X-ray polarimetry extremely appealing. There is a number of confirmed hard X-ray polarimetry experiments which along with the existing instruments (AstroSat and INTEGRAL) makes this field further exciting. Polarization experiments may also see a significant progress in sensitivity with new developments in scintillator readouts, active pixel sensors, CZT detectors. In particular, the advent of hard X-ray focusing optics, will enable designing of compact focal plane polarimeters with a multifold enhancement in sensitivity. In this review, we will focus on the recent polarimetry findings, science potential of hard X-ray polarimetry along with possible improvements in the measurement techniques.