Synthetic Light Curves and Spectra for the Photospheric Phase of a 3D Stripped-Envelope Supernova Explosion Model

TL;DR

This study performs 3D Monte Carlo radiative-transfer calculations (Artis) on a self-consistent ultra-stripped core-collapse SN model to produce synthetic light curves and spectra during the photospheric phase. It finds a fast, faint transient with a peak bolometric luminosity of about $L_{ ext{p}} \approx 8.4\times10^{41}$ erg s$^{-1}$ and $\Delta m_{15}$ in the range $1{-}2$ mag, with a strong viewing-angle dependence of ~1 mag due to a large-scale dipole in $^{56}$Ni distribution. The synthetic spectra are Mg II-dominated, with notable O I, C, Si, and Ca features, but do not resemble observed Ib/c spectra, partly due to NLTE limitations and missing forbidden lines. The results highlight how nickel-blob geometry and low ejecta mass can shape early photometry, offering a potential diagnostic of explosion asymmetries, though the extreme asymmetry may limit direct comparisons to typical Ib/c SNe and motivates broader model sets in future work.

Abstract

We present synthetic light curves and spectra from three-dimensional (3D) Monte Carlo radiative transfer simulations based on a 3D core-collapse supernova explosion model of an ultra-stripped $3.5\,\mathrm{M}_{\odot}$ progenitor. Our calculations predict a fast and faint transient with $Δm_{15} \sim 1\texttt{-} 2\,\mathrm{mag}$ and peak bolometric luminosity between $-15.3\,\mathrm{mag}$ and $-16.4\,\mathrm{mag}$. Due to a large-scale unipolar asymmetry in the distribution of $^{56}\mathrm{Ni}$, there is a pronounced viewing-angle dependence with about $1\,\mathrm{mag}$ difference between the directions of highest and lowest luminosity. The predicted spectra for this rare class of explosions do not yet match any observed counterpart. They are dominated by prominent Mg~II lines, but features from O, C, Si, and Ca are also found. In particular, the O~I line at \wl{7}{774} appears as a blended feature together with Mg~II emission. Our model is not only faster and fainter than the observed Ib/c supernova population, but also shows a correlation between higher peak luminosity and larger $Δm_{15}$ that is not present in observational samples. A possible explanation is that the unusually small ejecta mass of our model accentuates the viewing-angle dependence of the photometry. We suggest that the viewing-angle dependence of the photometry may be used to constrain asymmetries in explosion models of more typical stripped-envelope supernova progenitors in future.

Figures (18)

• Figure 1: Pre-supernova composition of the progenitor before the onset of core collapse. Only selected elements in the outer part of the iron core and the outer shell are shown.
• Figure 2: Spherically averaged composition of the 3D explosion model before mapping to the 3D Cartesian grid in Artis , showing how
• Figure 3: Comparison of the bolometric and UBVRI light curves showing the comparison to the model with increased nickel mass. Orange curves show the results for the baseline model.
• Figure 4: Peak bolometric magnitude for different observer viewing angles. This is the peak magnitude that different observers would measure at slightly different peak times (see Figure \ref{['fig:vangle_all_plight']}) based on the flux in their observer direction.
• Figure 5: Time of peak bolometric luminosity as a function of viewing angle.