UC Santa Barbara

Over 10,000 astronomical transients are now discovered every year. Pairing this wealth of objects with rapid followup facilities such as Las Cumbres Observatory (LCO) allows for high-cadence multiwavelength characterization of supernovae (SNe) within days or even hours of their explosion. Although Type Ia SNe (SNe Ia) are a relatively homogeneous population around peak brightness, notably used as standardizable candles to measure cosmological parameters, at early times their lightcurves show a dramatic range of behavior. One effect sometimes visible in their early lightcurves is a UV excess, likely indicative of the exploding white dwarf having a nondegenerate companion which shocks the SN ejecta as the two collide. Studying their varied early lightcurves can thus reveal information about their progenitor systems, which remain poorly understood beyond the fact that the explosion originates from a white dwarf. Here I present three advancements in SNe Ia research: (1) SN 2019yvq is a SN Ia which displayed the strongest early UV excess ever observed in SNe Ia. This SN shared some characteristics with a rare subclass of SNe Ia called 02es-likes, which for some reason seem to display these excesses more frequently than their predicted rarity. (2) In a sample of 9 SNe Ia with excellent early data from LCO, the distribution of early excess strengths and best-fit viewing angles are consistent with the progenitor systems of SNe Ia predominantly containing a nondegenerate companion. (3) In a sample of 127 SNe Ia observed by the ZTF survey, the rate of early excesses is again consistent with the single-degenerate progenitor scenario.