Joe Hill/Universities Space Research Association
A Gamma-ray Burst Photoelectric Polarimeter

We propose to develop a hard X-ray photoelectric polarimeter for prompt gamma-ray burst (GRB) emission in the 15-80 keV energy band. Linear polarization measurements would provide unique and important constraints on theories of GRB production mechanisms. The photoelectric polarimeter is based on a large-volume micropattern time-projection chamber that can determine, on a photon-by-photon basis, the angle of emission of the photoelectron resulting from an X-ray interaction. The photoelectron emission direction is correlated with the X-ray electric field vector and thus provides polarization information. This polarimetry technique combines high sensitivity with broad bandpass and is potentially the most powerful method below about 80 keV, where the photoelectric effect is the dominant interaction process. The proposed effort includes the development and testing of both detector hardware and simulation and analysis tools. It is expected that this effort would lead to a follow-on proposal for either a long duration balloon flight or other mission of opportunity.