OH Observations of Comet Hale-Bopp at 1.667 GH[CLC]z[/CLC] and Maser Amplification of a Background Source by the Comet

Abstract

OH spectra of comet Hale-Bopp were obtained at 1.667 GHz between 1997 February 19 and June 1 using the 26 m parabolic antenna of the Dominion Radio Astrophysical Observatory. Spectra showed strong (2 Jy) emission in mid-February. The comet's flux density then decreased, until it was barely detectable by March 11. An absorption line dominated the spectrum for several days in March. Flux density remained low for most of the subsequent observations. At the end of April a strong emission line appeared close to the expected cometary velocity. It is argued that this line did not arise in the comet itself, but came from a background source, probably IRAS 04361+2547, whose radiation had undergone maser amplification in the coma of the comet.