Abstract: Polarization has been a powerful diagnostic tool in radio, microwave, and visible astronomy, providing details of photonproduction mechanisms on much smaller scales than can bedirectly imaged or deduced from photon intensity and energyalone. While polarimetry at other these wavebands (radio,microwave, and optical) is an established technique, highenergy astrophysics lags far behind in this respect. Yet polarizationanalysis has the potential of revealing many detailsabout the magnetic fields, …