SN2023ixf: Radiative-transfer modeling of the photospheric phase evolution from the ultraviolet to the infrared

TL;DR

This study presents comprehensive radiative-transfer modeling of SN2023ixf's photospheric phase from UV to IR, revealing the importance of CSM interaction, asymmetry, and clumping effects in understanding its spectral evolution.

Contribution

First detailed radiative-transfer models covering UV to IR for SN2023ixf, highlighting CSM interaction, asymmetry, and clumping impacts on spectral features.

Findings

Progenitor star had 15Msun with enhanced mass loss, ejecting 7-8Msun of material.

Prolonged CSM interaction explains persistent UV continuum and IR flux.

Asymmetry and clumping significantly influence spectral line profiles and model sensitivity.

Abstract

SN2023ixf, a Type II supernova (SN) showing early signs of interaction with circumstellar material (CSM), has been observed with unprecedented detail across the electromagnetic spectrum since shock breakout. Here, we present nonlocal thermodynamic equilibrium time-dependent radiative-transfer calculations of its photospheric-phase evolution (i.e., ~20 to ~120d), and for the first time encompassing from the ultraviolet (UV) to the infrared (IR). The explosion of a 15Msun progenitor star, evolved with enhanced mass loss during the red-supergiant phase, yielding an ejecta of 7-8Msun, a kinetic energy of 1.2x10^51 erg, and a 56Ni mass of 0.05Msun, yields a satisfactory match to the photospheric-phase duration and brightness. Prolonged interaction with a decreasing CSM density is required to match a number of salient features of SN2023ixf during the photospheric phase, including the persistent UV continuum and line fluxes, the optical brightness and line profiles (in particular Halpha), as well as the IR flux (interaction boosts the free-free emission at long wavelengths). The presence of a cold dense shell (CDS), which is hard to infer at early times when the CDS and photosphere lie at similar velocities, becomes evident at later times and more so in the IR - we find no evidence for material faster than the CDS at ~8000km/s. Exploratory two-dimensional radiative-transfer calculations based on axially symmetric CSM or ejecta suggest that asymmetry can produce a diversity of profile shapes, with absorption troughs exhibiting a flat bottom or notches at any Doppler velocity. We emphasize the complexity of UV spectra influenced by complex metal-line blanketing at these phases. We document the sensitivity of model results to the adopted clumping in the CDS, though the largest offset is obtained here in the unlikely case of a smooth CDS.