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

J. Burke, D. A. Howell+15 more|arXiv (Cornell University)|Jan 15, 2021

Gamma-ray bursts and supernovae171 references36 citations

TL;DR

This study presents early UV and optical photometric and spectroscopic data of the nearby Type Ia supernova SN 2019yvq, which exhibits an extreme ultraviolet excess within days of explosion—brighter than its optical peak. Despite modeling with ejecta-companion shock and sub-Chandrasekhar double-detonation models, no single model fully reproduces all observed features, suggesting 02es-like SNe Ia require progenitor systems capable of isotropic UV emission, challenging standard viewing-angle-dependent shock models.

ABSTRACT

We present photometric and spectroscopic observations of the nearby Type Ia SN 2019yvq, from its discovery $\sim$1 day after explosion to $\sim$100 days after its peak brightness. This SN exhibits several unusual features, most notably an extremely bright UV excess seen within $\sim$5 days of its explosion. As seen in Swift UV data, this early excess outshines its "peak" brightness, making this object more extreme than other SNe with early UV/blue excesses (e.g. iPTF14atg and SN 2017cbv). In addition, it was underluminous ($M_B=-18.4$), relatively quickly declining ($\Delta m_{15}(B)=1.35$), 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, nebular [Ca II]). We model this dataset with a variety of published models, including SN ejecta - companion shock interaction and sub-Chandrasekhar mass WD double detonation models. Radio constraints from the VLA place an upper limit of $(4.5 - 20) imes 10^{-8}$ M$_{\odot}$/yr 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 dataset, 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.

Motivation & Objective

• To characterize the early-time UV and optical lightcurves and spectra of SN 2019yvq, a nearby Type Ia supernova with an unusual early UV excess.
• To determine whether the extreme UV excess can be explained by standard progenitor models, such as ejecta-companion shock interaction or sub-Chandrasekhar double-detonation.
• To assess the implications of the UV excess for the progenitor system, including constraints from radio observations on mass-loss rates.
• To evaluate whether the observed properties of SN 2019yvq are consistent with the 02es-like subclass of Type Ia supernovae.

Proposed method

• Acquired high-cadence photometric and spectroscopic data from Las Cumbres Observatory, Swift UVOT, ZTF, and other ground-based telescopes from ~1 day after explosion to ~100 days post-peak.
• Corrected photometry for extinction using the Milky Way extinction law and applied K-corrections to derive absolute magnitudes.
• Compared lightcurves and spectral features with published models, including Kasen (2010) ejecta-companion shock models and Polin et al. (2019a) sub-Chandrasekhar double-detonation models.
• Used radio observations from the VLA to constrain mass-loss rates from a potential symbiotic progenitor, placing an upper limit of (4.5–20) × 10⁻⁸ M⊙/yr.
• Analyzed nebular spectra to search for emission lines of [Fe II] and [Ca II], and used these to assess nucleosynthetic yields and potential double-detonation signatures.
• Performed lightcurve fitting using SNooPy and emcee to compare observed and modeled lightcurves, assessing goodness-of-fit across multiple bands.

Experimental results

Research questions

• RQ1 Can the extreme early UV excess in SN 2019yvq be explained by ejecta-companion shock interaction, as predicted by Kasen (2010)?
• RQ2 Do the observed lightcurve and spectral features of SN 2019yvq align with models of sub-Chandrasekhar mass WD double detonations?
• RQ3 Why are early UV excesses common in 02es-like SNe Ia, given that viewing-angle effects should limit such signatures to only ~10% of events?
• RQ4 What constraints do radio observations place on the presence of a non-degenerate companion, such as a red giant or main sequence star?
• RQ5 Can a single progenitor model reproduce the full dataset of SN 2019yvq, including its UV excess, broad Si II features, and nebular emission lines?

Key findings

• SN 2019yvq exhibits an extreme UV excess within ~5 days of explosion, with UV flux exceeding its optical peak magnitude, making it more extreme than other known early UV excess SNe like iPTF14atg and SN 2017cbv.
• The supernova is underluminous (MB = −18.4), rapidly declining (∆m15(B) = 1.35), and shows red colors after its early blue bump, distinguishing it from normal SNe Ia.
• Spectroscopic features include extremely broad and high-velocity Si II absorption, strong nebular [Fe II] and [Ca II] emission, and no detectable H or He, indicating a carbon-oxygen white dwarf progenitor.
• Radio observations from the VLA place an upper limit of (4.5–20) × 10⁻⁸ M⊙/yr on the mass-loss rate from a potential symbiotic companion, which does not rule out a red giant or main sequence star.
• No single model—whether ejecta-companion shock or sub-Chandrasekhar double-detonation—can fully reproduce all observed features of SN 2019yvq, indicating the need for more complex progenitor systems.
• The ubiquity of early UV excesses in 02es-like SNe Ia suggests progenitor systems must produce isotropic UV emission, challenging the standard viewing-angle-dependent shock model and favoring mechanisms like circumstellar matter or bipolar jets.