Are supernova remnants quasi-paralll or quasi-perpendicular accelerators?

Observations of shock waves in the solar system show a pronounced difference in the plasma wave and particle environment depending on whether the shock is propagating along or perpendicular to the interplanetary magnetic field. Quite different theories for particle acceleration have been developed for quasi-parallel and quasi-perpendicular shocks. Extension of these ideas to the interstellar medium would lead one to believe that the relativistic electrons in radio supernova remnants are accelerated by either the Q-parallel of Q-perpendicular mechanism. If this is the case, the observed morphology of a remnant should depend on the angle PHI between the line of sight and the galactic magnetic field at the position of the remnant. The dependence of observed structure on this angle will be quite different for Q-parallel and Q-perpendicular mechanisms. We have used a model for the galactic magnetic field and published maps of supernova remnancts to search for a dependence of structure of the angle Φ. We did not find a tendency for the remnants as a whole to favor the relationship expected for either mechanism, although individual sources resembled model remnants of one or the other acceleration process. We will discuss a number of possible explanations for this result is discusses. (author). 6 refs.; 2 figs