The New Status Qvo? SN 2021qvo is Another 2003fg-like Type Ia Supernova with a Rising Light-Curve Bump

TL;DR

SN 2021qvo is identified as a 2003fg-like Type Ia supernova with a clearly observed early-time rising bump. The authors combine multi-band, pre-peak photometry and a time-series of spectra, modeling the bump with a CSM interaction framework using MOSFiT's csmni model, yielding a best-fit ${\log_{10}(M_{\mathrm{CSM}}/M_\odot) = -2.33^{+0.26}_{-0.15}}$ and a CSM onset at $\sim$0.05–4 AU. The analysis places SN 2021qvo firmly within the 2003fg-like class on photometric and spectroscopic grounds, and its CSM mass is consistent with other rising-bump SNe Ia, reinforcing the role of CSM interaction in this subpopulation. As more such events are discovered and analyzed, population-level inferences on CSM properties will better constrain the progenitor scenarios for these luminous, broad SNe Ia.

Abstract

In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with ''bumps'' in their rising light curves shortly after explosion. Here, we present SN 2021qvo: a SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Si II $λ$5972 pseudo-equivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called ''super-Chandrasekhar") SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient pre-peak data to reveal a rising light-curve bump, and all four have bump detections. Host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy ${\rm log}(M_{\ast}/M_{\odot}) = 7.83^{+0.17}_{-0.24}$, also consistent with other members of this class. The current leading early-bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the range $M_\mathrm{CSM}=3.31-8.51 \times 10^{-3} M_\odot$. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia.

Figures (14)

• Figure 1: SN 2021qvo observations in different filters, plotted as days from the $g$-band peak (MJD=59401.2) versus the observed magnitude. Downward-facing triangles denote upper limits. The inset shows a zoomed-in portion of the light curve in flux space from $-20$ to $-15$ days before peak, showing the early time light-curve bump.
• Figure 2: SNooPy fits for all ten bands of SN 2021qvo. Plotted as time from $B$-band peak given by SNooPy versus the observed magnitude. Upper limits were removed when fitting the light curve.
• Figure 3: Color evolution plot for SN 2021qvo in the $\it{r-i}$ and $\it{g-r}$ bands. The data used are from the $g$, $r$, and $i$ bands collected by Pan-STARRS. A comparison is made using other confirmed 2003fg-like SNe Ia derived from the Carnegie Supernova Project Ashall_2021, as well as a normal type SN Ia SN 2011fe. Curves were not corrected for host-galaxy extinction.
• Figure 4: Luminosity Width Relation, $i.e.$ Phillips relation Phillips_1999, plot for SN 2021qvo and multiple 2003fg-like events, showing the relationship between the color stretch parameter $s_{BV}$ and the absolute magnitude in the $B$-band $M_{B,max}$. The background sample of normal SNe Ia (grey squares) is taken from Burns_2018. SN 2021qvo is shown as a purple star. We increased the error in SN 2021qvo's $M_{B,max}$ to account for the sources of underluminosity detailed in Section \ref{['subsection:LWR']}. All other colored triangles are confirmed 2003fg-like events that have measurements in the $B$-band. These events have been corrected for Milky-Way extinction.
• Figure 5: Color--stretch parameter $s_{gr}$ as a function of the $g$-band maximum relative to the $i$-band maximum. SN 2021qvo (purple) can be seen in the top right. Approximate boxes are laid out to coincide with the classifications of different SN Ia subtypes Ashall_2020. Diagram derived from Figure 3 in Ashall_2020.