Supernova interactions with aspherical circumstellar material I: calculations of light curves, AB magnitudes, spectra, and polarisation

TL;DR

This work develops 2D axisymmetric radiation-hydrodynamics simulations of SN ejecta interacting with strongly aspherical CSM in disc and bipolar-lobe geometries, and combines CASTRO with Monte Carlo radiative transfer (SEDONA and SIROCCO) to produce direction-dependent light curves, AB magnitudes, spectra, and polarisation. By mapping a 1D SNEC SN model into CASTRO and exploring five stratified CSM configurations (two discs, three lobes), the study reveals distinct dynamical and observational signatures linked to morphology, including slower ejecta expansion in dense CSM, smooth versus two-peak light curves, angle-dependent spectral features, and modest polarisation. The results provide qualitative guidance for interpreting Type IIn SNe and for constraining pre-SN mass loss geometries, while highlighting limitations and pathways for refinement, such as dust physics and parsec-scale domain extension. Together, the framework enables weeding out viable CSM configurations and informs future UV observations and model improvements for SN–CSM interaction scenarios.

Abstract

We present an upgraded detailed numerical calculations of supernova (SN) interactions with significantly aspherical circumstellar matter (CSM), primarily formed as a disc or bipolar lobes. The circumstellar disc can arise as a result of, for example, mass transfer in a binary, while bipolar lobes can be the result of a violent pre-explosive ejection of matter, similar to the iconic cases of luminous blue variable stars (LBVs). We numerically simulate the radiation-hydrodynamic (RHD) behaviour of interaction processes using a 2D cylindrical version of the RHD code CASTRO. We then calculate light curves, spectral patterns, and polarisation profiles, all up to a relatively long time of two years after an SN shock breakout and from different directions, using the multidimensional Monte Carlo radiation transfer (MC-RT) codes SEDONA and SIROCCO. We calculated a total of five models for the two aforementioned configurations of the surrounding CSM, for stratified density levels, comparing the simulated hydrodynamic behaviour and differences in their observable properties. RHD models exhibit similar behaviour to previous adiabatic models, but with a significantly slower expansion velocity. The calculated light curves show a relatively smooth evolution in SN-disc interaction, and declines and brightening in SN-lobes interaction. Comparing models with real events with a presumed similar physical process provides guidance for selecting a more accurate CSM configuration when simulating real situations.

Figures (14)

• Figure 1: Model DMIN. Selected evolutionary stages of SN interaction with a "thinner" circumstellar disk calculated by the RHD code. The four columns show the snapshots at times $t = 0$, $240$, $480$, and $730$ days. The individual rows shows four different quantities: from top to bottom it is density $\rho$, velocity magnitude $v$, temperature $T$, and radiative energy density $E_r$. The resolution of the bitmaps had to be significantly reduced compared to resolution of the simulations in order to reduce the file size. For the animated version of this image, see Appendix \ref{['animasect']}.
• Figure 2: Model LMIN. Selected evolutionary stages of the SN interaction with the "thinnest" bipolar lobes structure calculated by the RHD code. The four columns show the snapshots at times $t = 0$, $240$, $480$, and $730$ days. The individual rows show four different quantities: from top to bottom it is density $\rho$, velocity magnitude $v$, temperature $T$, and radiative energy density $E_r$. For the animated version of this image, see Appendix \ref{['animasect']}.
• Figure 3: Pseudo-bolometric, directionally "observed" LCs of the two models of SN interaction with circumstellar disk-like structures, denoted as model DMIN ( left panel) and model DMAX ( right panel), up to approx. 2 years (see Sects. \ref{['rhdsetdisk']} and \ref{['SNdiskLCs']}). The upper pair of lines shows the LCs calculated within the "largest" frequency range $10^{14}$–$2\times 10^{16}$ Hz (see Sect. \ref{['MCRTdescr']}), while the bottom pair of lines shows the same within the range ($3.875$–$7.825$)$\,\times 10^{14}$ Hz, which roughly corresponds to the frequency range of visible light (for LCs corresponding to AB magnitudes in main filters, see Fig. \ref{['disk_third']}). We demonstrate here the LC profiles for two different viewing angles in the graphs, the pole-on (polar) view marked in blue and the equatorial view marked in dashed black line for the bolometric LC (labelled $L_\text{bol}$ in the legend), and the polar view marked in red dash-dotted line and the equatorial view marked in dotted black line for the visual LC (labelled $j_\text{vis}$ in the legend). The black solid line labelled "no CSM" corresponds to an SN without CSM interaction, heated with $0.28\,M_\odot$ of radioactive Ni which roughly corresponds to the brightest normal H-rich SNe pejcha152017ApJ...841..127M or the population mean of stripped SNe anderson19.
• Figure 4: Calculated AB magnitudes for the two models of SN interaction with the circumstellar disk-like morphology. Each row in the figure corresponds to one of the models DMIN or DMAX labelled on the right. The three columns demonstrate the three various viewing angles marked at the top. The AB magnitudes are calculated for nine filters listed in the left top and bottom panels.
• Figure 5: Pseudo-bolometric, directionally "observed" LCs of the three models of SN interaction with bipolar lobes structure, denoted as model LMIN ( left panel), model LMOD ( middle panel), and model LMAX ( right panel), up to approx. 2 years (see Sects. \ref{['rhdsetlobes']} and \ref{['SNlobesLCs']}). The meaning and structure of the image, the order and types of lines, and the legend are the same as in Fig. \ref{['disk_lbolfirst']}.