The Absorption by the Interstellar Medium of 80 MHz Radio Emission from Galactic Supernova Remnants

Abstract

High resolution 80 MHz observations of 20 galactic supernova remnants have been made with the Culgoora radioheliograph. More than half of the sources have an unexpectedly low flux density at 80 MHz, probably as a result of free?free absorption taking place in the inner arms of the Galaxy. The observations imply an r.m.s. electron density of about 0·1?0·5 cm?3 along the line of sight. This large value for the electron density seems to require a greater ionizing flux than that which occurs in the solar vicinity.