Gamma-Ray Polarimetry of Two X-Class Solar Flares

We have performed the first polarimetry of solar flare emission at γ-ray energies (0.2–1MeV). These observations were performed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for two large flares: the GOES X4.8-class solar flare of 2002 July 23, and the X17-class flare of 2003 October 28. We have marginal polarization detections in both flares, at levels of 21 ± 9% and -11 ± 5% respectively. These measurements significantly constrain the levels and directions of solar flare γ-ray polarization, and begin to probe the underlying electron distributions. Subject headings: gamma rays: solar flares — polarization — RHESSI