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K. R. Healy, J. J. Hester (ASU), R. Braun (NFRA), J. C. Raymond (CfA)
We present C-band VLA radio observations of a region on the eastern edge of the Cygnus Loop supernova remnant. The field observed includes a feature dubbed the ``Spur'' by Hester, Parker, and Dufour (1983), and studied in great detail by Raymond et al. (1988). This study was able to independently determine the ram pressure driving the shock and the thermal pressure in the post-shock recombination region, and found that the ratio of these two pressures was close to a factor of 10. This difference was interpreted as being due to support of the recombination region by magnetic fields and cosmic rays.
Since radio emission behind radiative shocks arises in the same volume of space as emission in lines such as H\alpha and [S II], the radio data can be combined with the earlier work to determine the radio volume emissivity. This, together with the nonthermal pressure, establishes a relationship between the magnetic field strength and the cosmic ray proton/electron ratio. With the additional constraint that the magnetic field and known thermal electron density provide the observed Faraday depolarization in the region, we are able to obtain values for the field strength, the pressure in cosmic ray electrons, and the pressure in cosmic ray protons. Preliminary analysis of these data suggest that the field and particles behind this supernova remnant shock wave are close to equipartition, with a ratio of cosmic ray proton to electron pressures in the neighborhood of 100:1.
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