Evidence of weak circumstellar medium interaction in the Type II SN 2023axu

TL;DR

This paper presents detailed early observations of SN 2023axu, a Type II supernova, revealing weak circumstellar medium interaction through light curve modeling and spectral features, highlighting the importance of high-cadence data for understanding progenitor mass loss.

Contribution

The study provides the first detailed early-time photometric and spectroscopic analysis of SN 2023axu, identifying signs of circumstellar interaction not captured by standard shock cooling models.

Findings

Early spectra show features indicative of circumstellar interaction.

Shock cooling model underpredicts UV and early light curve rise.

Spectral features suggest recent mass loss from the progenitor.

Abstract

We present high-cadence photometric and spectroscopic observations of SN~2023axu, a classical Type II supernova with an absolute $V$-band peak magnitude of $-16.5 \pm 0.1$ mag. SN~2023axu was discovered by the Distance Less Than 40 Mpc (DLT40) survey within 1 day of the last non-detection in the nearby galaxy NGC 2283 at 13.7 Mpc. We modeled the early light curve using a recently updated shock cooling model that includes the effects of line blanketing and found the explosion epoch to be MJD 59971.48 $\pm$ 0.03 and the probable progenitor to be a red supergiant with a radius of 417 $\pm$ 28 $R_\odot$. The shock cooling model cannot match the rise of observed data in the $r$ and $i$ bands and underpredicts the overall UV data which points to possible interaction with circumstellar material. This interpretation is further supported by spectral behavior. We see a ledge feature around 4600 \AA\ in the very early spectra (+1.1 and +1.5 days after the explosion) which can be a sign of circumstellar interaction. The signs of circumstellar material are further bolstered by the presence of absorption features blueward of H$\alpha$ and H$\beta$ at day $>$40 which is also generally attributed to circumstellar interaction. Our analysis shows the need for high-cadence early photometric and spectroscopic data to decipher the mass-loss history of the progenitor.