SN 2023zcu: A Type IIP SN with Early Flash Features

TL;DR

This study presents a detailed, multi-epoch photometric and spectroscopic investigation of SN 2023zcu, a Type IIP supernova in NGC 2139. By combining shock-cooling modeling of the early light curve, TARDIS radiative-transfer spectral fits, and a tailored expanding photo-sphere method, the authors derive a distance of ~27.8 Mpc, an explosion epoch near MJD 60285.6, and a progenitor radius around 1200 Rsun. Nebular-phase spectroscopy and bolometric-light-curve modeling jointly constrain a progenitor mass in the 12–15 Msun range and an ejecta mass near 10 Msun with a 56Ni mass of ~0.023 Msun, consistent across independent methods. The results place SN 2023zcu among normal IIP events with modest CSM interaction, reinforcing the connection between Type IIP SNe and red supergiant progenitors in the 12–15 Msun range and illustrating the power of integrated photometric-spectroscopic analysis for constraining explosion physics and progenitor properties.

Abstract

We present a detailed photometric and spectroscopic analysis of the Type IIP supernova SN~2023zcu, which exploded in the galaxy NGC~2139 (redshift $z$ = 0.006). SN~2023zcu exhibits a well-sampled light curve covering the rise, plateau, and nebular phases. It has an optically thick phase of $100.6 \pm 0.6$ d with a magnitude drop of $\sim$1.7 mag in the {\em V} band during the transition between the plateau and the nebular phases. Weak emission features in the early-time spectra indicate a low-level interaction between circumstellar material (CSM) and the SN ejecta. The spectral evolution is well sampled and exhibits a prominent P-Cygni profile of H$α$, a defining characteristic of Type IIP SNe. Signatures of metal-line formation (e.g., \ion{Fe}{2}, \ion{Ca}{2} near-infrared triplet) are also evident in the spectra as the SN evolves. Spectral modeling with the radiative-transfer code \texttt{TARDIS} during the early photospheric phase (8.7--35.5 d since explosion) yields photospheric temperatures decreasing from $\sim$9,000 to $\sim$6,000 K and expansion velocities declining from $\sim$10,000 to $\sim$5,400 km s$^{-1}$. A tailored expanding photosphere method (EPM) fit based on the \texttt{TARDIS} models provides a distance estimate of $27.8 \pm 2.0$ Mpc. Nebular-phase spectra and bolometric light-curve modeling suggest a progenitor mass in the range 12--15 M$_\odot$. This thorough analysis helps to constrain progenitor properties and explosion parameters, thereby strengthening our understanding of Type IIP SNe.

Figures (17)

• Figure 1: Color composite image of SN 2023zcu, created using g, r, and i filters, observed with the 1 m telescope of Las Cumbres Observatory on December 18, 2023. The SN is marked in white, along with the positions of two other SNe (1995ad and 2022qhy) previously discovered in the same galaxy, NGC 2139.
• Figure 2: The early-time light curve modeling is performed using the shock-cooling model proposed by Sapir_Waxman_2017, implemented in the Python code described in hosseinzadeh_2020. The 100 best fits generated in this model using MCMC are presented along with the observed light curves.
• Figure 3: UV and optical light curves in apparent and absolute magnitude scales of SN 2023zcu. The Swift/UVOT light curves are shown in the inset. The photometric data span from 1.25 to $\sim$416 d, covering the different phases of the SN. The spectral epochs are denoted with red lines at the bottom. The 100 best-fit model light curves derived from the analytical model Valenti_2016 in the V band using MCMC, are shown as red lines. (Data used to create this figure is available.)
• Figure 4: Correlations between $a_0$, $t_{\rm PT}$ and $M_{V50}$. The red star represents SN 2023zcu, while the blue circles denote the SNe in the samples of Anderson_2014 and Valenti_2016.
• Figure 5: Top panel: The absolute V band light curve of SN 2023zcu compared with the SNe of the comparison sample. The gray lines represent the light curves from Anderson_2014. The vertical lines at 80 and 120 d represent the typical plateau duration for normal-plateau SNe. SN 2023zcu has a peak absolute magnitude of $-16.54\pm0.01$ in the V band, with a plateau length of $\sim$100 d, placing it in the category of intermediate luminosity normal-plateau SN. Bottom panel: The Swift/UVOT absolute magnitude light curves of SN 2023zcu (black stars) compared with a Type II SNe sample (grey points) taken from the SOUSA. All UVOT magnitudes are in Vega, corrected only for Milky Way extinction.