The Spectrum of SN 1972e and the Fluorescence Theory of Supernova Light

Abstract

Several years ago two of us proposed an explanation for the SN I light curve based on a fluorescence mechanism (Morrison and Sartori 1966, 1969). According to our model, the observed broad spectral features represent fluorescence excited in the medium surrounding the supernova by a pulse of soft x-rays produced in the explosion. The time behavior of the intensity measured by a fixed observer reflects the spatial attenuation of the primary pulse; for a single line and uniform density of absorbing material, the light curve is given by an exponential integral, which behaves asymptotically as e ^−x/x. With the dominant photographic band identified as He ii 4686, the most elementary version of the theory gives an excellent one-parameter fit to the photographic light curve from about 40 days on. The redward shift of the dominant feature is also naturally accounted for. The principal demands of the theory are:

• (i) some tenths of a solar mass of helium must have been ejected over the integrated history of the pre-supernova, and must have diffused out to fill a region a light year or two in radius;

• (ii) approximately 10⁵¹ erg is required in the exciting pulse in the energy range 50–54 eV. This leads to an estimate of ~ 10⁵² erg as a lower limit on the energy associated with the explosion.