A Light Echo from Type Ia SN 1995E?

Abstract

We identify a light echo candidate from Hubble Space Telescope (HST) imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E. From the echo's angular size and the estimated distance to the host galaxy, we find a distance of 207 ± 35 pc between the dust and the site of the supernova. If confirmed, this echo brings the total number of observed nonhistorical Type Ia light echoes to three—the others being SN 1991T and SN 1998bu—suggesting that they are not uncommon. We compare the properties of the known Type Ia supernova echoes and test models of light echoes developed by Patat and coworkers. HST photometry of the SN 1991T echo shows a fading, which is consistent with scattering by dust distributed in a sphere or shell around the supernova. Light echoes have the potential to answer questions about the progenitors of Type Ia supernovae, and more effort should be made for their detection, given the importance of Type Ia supernovae to measurements of dark energy.