[Ne v ] Imaging of the Cygnus Loop

Abstract

We present continuum-subtracted images of a 20 ' x20 ' region of the eastern Cygnus Loop (NGC 6995) in the 3425 Å forbidden line of Ne V. The images reveal bright linear filaments which are associated with, but not positionally coincident with, bright features seen in Hα, [O III], and other narrowband images. In some areas, the [Ne V] filaments define the edge of X-ray-emitting regions. The filaments exhibit a peak surface brightness of 1.2x10 -4 photons cm -2 s -1 arcsec -2 at the top of the atmosphere in images with typical detection limits of ~10 -5 photons cm -2 s -1 arcsec -2. We present arguments that these structures are produced by radiative shock waves and discuss implications for the shock velocities and the three-dimensional structure of this section of the Cygnus Loop. We place limits on the importance of thermal conduction-driven evaporation as a contribution to the mass of X-ray-emitting gas. Lack of evidence of [Ne V] emission resulting from thermal evaporation may have significance for supernova remnants and interstellar medium models that rely heavily on the importance of thermal evaporation.