H-alpha images of the Cygnus Loop - A new look at shock-wave dynamics in an old supernova remnant

Abstract

Deep Ha images of portions of the east, west, and southwest limbs of the Cygnus Loop are presented which illustrate several aspects of shock dynamics in a multiphase interstellar medium. An Ha image of an isolated eastern shocked cloud reveals cloud deformation and gas stripping along the cloud’s edges, shock front diffraction and reflection around the rear of the cloud, and interior remnant emission due to upstream shock reflection. A faint Balmer-dominated filament is identified 30' further west of the remnant’s bright line of western radiative filaments (NGC 6960). This detection indicates a far more westerly intercloud shock front position than previously realized, and resolves the nature of the weak x-ray, optical, and nonthermal radio emission observed west of NGC 6960. Strongly curved Balmer-dominated filaments along the remnant’s west and southwestern edge may indicate shock diffraction caused by chock wave passage in between clouds.