Could There Be a Hole in Type Ia Supernovae?

In the favored progenitor scenario, Type Ia supernovae arise from a whitedwarf accreting material from a non-degenerate companion star. Soon after thewhite dwarf explodes, the ejected supernova material engulfs the companionstar; two-dimensional hydrodynamical simulations by Marietta et. al. show that,in the interaction, the companion star carves out a conical hole of openingangle 30-40 degrees in the supernova ejecta. In this paper we usemulti-dimensional Monte Carlo radiative transfer calculations to explore theobservable consequences of an ejecta-hole asymmetry. We calculate the variationof the spectrum, luminosity, and polarization with viewing angle for theaspherical supernova near maximum light. We find that the supernova looksnormal from almost all viewing angles except when one looks almost directlydown the hole. In the latter case, one sees into the deeper, hotter layers ofejecta. The supernova is relatively brighter and has a peculiar spectrumcharacterized by more highly ionized species, weaker absorption features, andlower absorption velocities. The spectrum viewed down the hole is comparable tothe class of SN 1991T-like supernovae. We consider how the ejecta-holeasymmetry may explain the current spectropolarimetric observations of SNe Ia,and suggest a few observational signatures of the geometry. Finally, we discussthe variety currently seen in observed SNe Ia and how an ejecta-hole asymmetrymay fit in as one of several possible sources of diversity.Comment: 11 pages, 9 figures, submitted to Ap