Constraints on Type Ia Supernova Progenitor Companions from Early Ultraviolet Observations with Swift

TL;DR

This study uses early UV observations from Swift to compare with models of SN Ia progenitor systems, constraining the nature and geometry of potential companion stars, and excluding certain red supergiant companions.

Contribution

It introduces a model-independent method to set upper limits on shock brightness, constraining progenitor companion types and viewing angles for SNe Ia.

Findings

Red supergiant companions are excluded at 95% confidence for most cases.

Constraints allow for main sequence companions but not red giants.

UV observations can effectively limit progenitor system configurations.

Abstract

We compare early ultraviolet (UV) observations of Type Ia Supernovae (SNe Ia) with theoretical predictions for the brightness of the shock associated with the collision between SN ejecta and a companion star. Our simple method is independent of the intrinsic flux from the SN and treats the flux observed with the Swift/Ultra-Violet Optical Telescope (UVOT) as conservative upper limits on the shock brightness. Comparing this limit with the predicted flux for various shock models, we constrain the geometry of the SN progenitor-companion system. We find the model of a 1 M_sun red supergiant companion in Roche lobe overflow to be excluded at a 95% confidence level for most individual SNe for all but the most unfavorable viewing angles. For the sample of 12 SNe taken together, the upper limits on the viewing angle are inconsistent with the expected distribution of viewing angles for RG stars as the majority of companions with high confidence. The separation distance constraints do allow MS companions. A better understanding of the UV flux arising from the SN itself as well as continued UV observations of young SNe Ia will further constrain the possible progenitors of SNe Ia.