A Late-time Radio Survey of Type Ia-CSM Supernovae with the Very Large Array

Abstract

Type Ia-CSM supernovae (SNe) are a rare and peculiar subclass of thermonuclear SNe characterized by emission lines of hydrogen or helium, indicative of a high-density circumstellar medium (CSM). Their implied mass-loss rates of $\sim 10^{-4}-10^{-1}$ M${}_{\odot }$ yr${}^{-1}$ (assuming $\sim 100\mathrm{km}{\mathrm{s}}^{-1}$ winds) from optical observations are generally in excess of values observed in realistic SN Ia progenitors. In this paper, we present an independent study of CSM densities around a sample of 29 archival Ia-CSM SNe using radio observations with the Very Large Array at 6 GHz. Motivated by the late ($\sim$2 yr) radio detection of the Ia-CSM SN 2020eyj, we observed old ($>$1 yr) SNe where we are more likely to see the emergent synchrotron emission that may have been suppressed earlier by free-free absorption by the CSM. We do not detect radio emission down to 3$\ddot{I}ƒ$ limits of $\sim$35 $\hat{I}¼$Jy in our sample. The only radio-detected candidate in our sample, SN 2022esa, was likely mis-classified as a Ia-CSM with early spectra, and appears more consistent with a peculiar Ic based on later-epochs. Assuming a wind-like CSM with temperatures between $2\times 10^4$ K and $10^5$ K, and magnetic field-to-shock energy fraction ($\hat{I}{\mu }_B$) = $0.01-0.1$, the radio upper limits rule out mass-loss rates between $\sim 10^{-4}-10^{-2}$ M${}_{\odot }$ yr${}^{-1}$ (100 km s${}^{-1}$)${}^{-1}$. This is somewhat in tension with the estimates from optical observations, and may indicate that more complex CSM geometries and/or lower values of $\hat{I}{\mu }_B$ may be present.

18 pages, 7 figures, 3 tables, accepted to ApJ