First Day of Type IIP Supernova SN 2013fs: Hα from Preshock Accelerated Gas

Abstract

Abstract: I explore the origin of an asymmetry of the Hα emission from a circumstellar (CS) shell around type IIP supernova SN 2013fs in the spectrum taken 10.3 h after the shock breakout. A spherical model of the Hα emission from the CS shell that takes into account a preshock gas acceleration by a supernova radiation permits us to successfully reproduce the Hα profile. Principal factors responsible for the Hα asymmetry are the high velocity of the accelerated CS preshock gas (∼3000 km s−1) and a low Hα Sobolev optical depth in a combination with an occultation of the Hα emission by the photosphere.