Broad emission lines from opaque electron-scattering environment of SN 1998S

Abstract

I propose that broad narrow-topped emission lines with full width at zero intensity >20000 km/s, seen in early-time spectra of SN 1998S, originate from a dense circumstellar gas and not from the supernova ejecta. The tremendous line width is the result of multiple scattering of the narrow line radiation on thermal electrons of the circumstellar shell with the Thomson optical depth of about 4 on 1998 March 6.