The application of polarimentric techniques to gamma ray astronomy

The analysis of X-ray and gamma ray emission from compact sources has until now been confined to spectral characteristics and time variabilities. However, often several different models can explain the observed phenomena equally well. Polarimetric observations have the diagnostic potential to discriminate between the different compact source models and can offer a unique insight into the nature of emission zones.The Monte-Carlo polarimetric Compton scattering algorithm has been validated and analysis techniques developed to determine the degree of linear polarization present in polarized datasets. The construction of a prototype 37 element module has allowed, for the first time, polarimetric measurements to be made with a pixellated detector plane. Predictions made from nuclear transition theory have matched both simulated and experimental data extremely well.Although not designed specifically as a gamma ray polarimeter, EIDOS could have obtained a sensitivity of ~10-6 ph s-1 cm-2 keV-1 to 100% polarized emission to the 3σ level for a 106 second observation. If GRB 930131 and GRB 940217 had been observed by EIDOS, the minimum detectable degree of linear polarization at the 3σ level in the 240 to 600 keV energy range, would have been 6.6% and 4.0% respectively. Emission from the individual components of the Crab pulsar does not appear to be strong enough to allow sensitive measurements to be made in a 106 second observation. A 3σ level detection of ~5% polarization from a solar flare is possible in a 100 second observation in the 240 to 600 keV and the 250 to 750 keV energy range.COMPTEL has a sensitivity of ~2 x 10-6 ph s-1 cm-2 keV-1 to 100% polarized emission at the 3σ level for a 14 day observation in the 750 keV to 4 MeV incident photon energy range. COMPTEL observations of GRB 930131 and GRB 940217 should be sensitive to a minimum detectable degree of linear polarization, at the 3σ level in the 750 to 1125 keV energy range, of 9.6% for both sources. Emission from the individual components of the Crab pulsar is not strong enough to allow sensitive measurements to be made in a 14 day observation. A 3σ level detection of ~5% polarization from a solar flare is possible in a 100 second observation in the 750 to 1125 keV and the 750 to 1500 keV energy range.