Rhessi Solar Flare Polarization Measurements in the 20-100 keV Energy Range
Abstract
Although 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. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine Germanium detectors. The Germanium detectors are segmented, with both a front and rear active volume. Low energy photons from the Sun (below about 100 keV) have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Other studies of flare polarization with RHESSI have relied on photons that scatter between Ge detectors, an approach that is sensitive at higher energies where photon statistics are considerably reduced. Although polarization measurements are greatly aided by the spacecraft rotation, the analysis of these lower energy data has proven to be difficult due to various systematic effects in the data, one of which is the azimuthal dependence of background rates associated with the earth X-ray albedo. Here we shall present the current status of the analysis, which now includes simulations of the albedo flux. The current analysis concentrates on data from the X4.3 flare that took place on 23 July 2002. We will review the major analysis issues and discuss prospects for future studies of other RHESSI events.
- Publication:
-
American Astronomical Society Meeting Abstracts #210
- Pub Date:
- May 2007
- Bibcode:
- 2007AAS...210.9301M