Solar flare hard X-ray and gamma-ray imaging spectro-polarimetry with GRIPS and SAPPHIRE/SHARPIE

To date, flare hard X-ray (HXR) and gamma-ray polarimetry is a poorly exploited field of Solar Physics.

The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) has already flown once on a high-altitude balloon payload from Antarctica in January 2016. Using a rotating monogrid eight meters in front of spatially-differentiated germanium strip detectors (3D-GeDs), GRIPS images the sun from ~40 keV to ~10 MeV, with a 12.5" resolution and ~1 degree FOV. It can also provide polarization information above ~150 keV.

The SolAr Polarimeter for Hard x-Rays (SAPPHIRE) is a spatially-integrated polarimeter module with a CubeSat form factor currently being proposed. It aims to extract polarization information from solar flare-generated HXRs (~5-100 keV). The SHARPIE (Solar HArd x-ray Polarimer/Imager Experiment) concept is an imager using several SAPPHIRE modules behind RHESSI-like bigrid subcollimators.

We shall review these instruments or instrument concepts and their capabilities and the science questions that they address, with an emphasis on the polarization measurements.