A Bright Ultraviolet Excess in the Transitional 02es-like Type Ia Supernova 2019yvq

We present photometric and spectroscopic observations of the nearby Type Ia SN 2019yvq, from its discovery similar to 1 day after explosion to similar to 100 days after its peak brightness. This SN exhibits several unusual features, most notably an extremely bright UV excess seen within similar to 5 days of its explosion. As seen in Swift UV data, this early excess outshines its peak brightness, making this object more extreme than other supernovae (SNe) with early UV/blue excesses (e.g., iPTF14atg and SN 2017cbv). In addition, it was underluminous M ( B ) = -18.4, relatively quickly declining (Delta m (15)(B) = 1.37), and shows red colors past its early blue bump. Unusual (although not unprecedented) spectral features include extremely broad-lined and high-velocity Si absorption. Despite obvious differences in peak spectra, we classify SN 2019yvq as a transitional member of the 02es-like subclass due to its similarities in several respects (e.g., color, peak luminosity, peak Ti, and nebular [Ca ii]). We model this data set with a variety of published models, including SN ejecta-companion shock interaction and sub-Chandrasekhar-mass white dwarf (WD) double-detonation models. Radio constraints from the VLA place an upper limit of (4.5-20) x 10(-8) M (circle dot) yr(-1) on the mass-loss rate from a symbiotic progenitor, which does not exclude a red giant or main-sequence companion. Ultimately, we find that no one model can accurately replicate all aspects of the data set, and further we find that the ubiquity of early excesses in 02es-like SNe Ia requires a progenitor system that is capable of producing isotropic UV flux, ruling out some models for this class of objects.

Automated summary

This study presents observations of the nearby Type Ia supernova 2019yvq, identifying several unusual features such as an extremely bright UV excess shortly after explosion. Despite efforts to model the data using various published models, no single model accurately captures all aspects of the observations, indicating the need for further research into the unique properties of this subclass of supernovae.