Stimulated emission of carbon recombination lines from cold clouds in the direction of Cassiopeia A

Abstract

Observations made at 10 frequencies in the 34-325-MHz range provide evidence for stimulated emission of carbon recombination lines in the direction of Cas A. Recombination lines have been detected in absorption below 115 MHz and in emission above 200 MHz. The observed intensities and widths of the lines have been employed to determine the properties of the intervening clouds and to constrain theoretical predictions of level populations in high quantum number states of carbon in cold clouds.