Prospects for hard X-ray solar flare polarimetry with RHESSI

Abstract

Designed primarily as a hard X-Ray imager and spectrometer the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-Rays (20-100 keV) from solar flares. These studies will provide the capability to probe the geometry of the acceleration process. Although not originally designed to study hard X-Ray polarization of solar flares, it was realized during the development of RHESSI that the essential ingredients for measuring the polarization, namely, an array of detectors in a rotating spacecraft, were already present. All that was needed was the addition of a strategically placed cylinder of Be in the cryostat to Compton scatter the hard X-Rays (20-100 keV) into the rear segments of the adjacent Ge detectors, since the direction of the scattering depends on the polarization of the incoming photon. Monte Carlo simulations indicate that a 20-100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares, by comparing the counting rates of these rear segments. © 2002 Elsevier B.V. All rights reserved.