The true extent of the Gamma Cygni supernova remnant

Abstract

Aperture-synthesis observations at 1.4 GHz show that the Gamma Cygni supernova remnant (SNR) has a shell structure of about 62-arcmin diameter, centered at Galactic longitude 78.2 deg, latitude +2.1 deg. Radio emission from the shell is strongest in the southeast quadrant, near the star Gamma Cygni, where it is concentrated in several tangentially elongated structures. A second region of enhanced nonthermal emission is in the northwest quadrant. Based on a brightness-diameter relation, the observed flux density of 270 + or - 40 Jy implies a diameter of approximately 33 pc and a distance of about 1.8 kpc. Thermal radio emission is observed from the Gamma Cygni Nebula which lies near Gamma Cygni and coincidentally near the peak emission of the SNR. The possible significance of the near positional agreement of the thermal and nonthermal radio sources is discussed.