Type IIP SN 2024bch: Hydrodynamic model, shock breakout, and circumstellar interaction

Abstract

The well-observed type IIP SN 2024bch with the short plateau is shown to be an outcome of the red supergiant explosion with the presupernova mass of 14-15 Msun, the explosion energy of 2x10^{51} erg, and presupernova radius of 1250 Rsun. The early gamma-ray escape demonstrated by the radioactive tail is due to the large Ni-56 extension up to 7400 km/s. The early-time spectral evolution indicates the presence of the circumstellar dense confined envelope with the mass of 0.003-0.006 Msun within 6x10^{14} cm. The deceleration of the outermost ejecta implies the wind with the mass-loss rate of about 6x10^{-4} Msun/yr. The inferred mass-loss rate is by one-two order larger compared to most of type IIP supernovae, but comparable to the wind of type IIL SN 1998S. The asymmetry of the broad H-alpha component on day 144 powered by the circumstellar interaction is the outcome of the Thomson scattering and absorption in the Paschen continuum in the unshocked ejecta.

Figures (9)

• Figure 1: The structure of the pre-SN model. Panel (a): the density distribution as a function of radius. At the radii $r > 10^{14}$ cm the density refers to CSM. Panel (b): the chemical composition. Mass fraction of hydrogen (black line), helium (blue line), CNO elements (green line), and Fe-peak elements excluding radioactive $^{56}$Ni (magenta line) in the ejected envelope. The central core of 1.6 $M_{\odot}$ is omitted.
• Figure 2: The bolometric light curve and the evolution of photospheric velocity. Panel (a): the model light curve (red line) overlaid on the bolometric data (circles) Andrews_2025. The black line is the total power of radioactive $^{56}$Ni decay. Panel (b): the evolution of model velocity defined by the level $\tau_{eff} = 2/3$ (blue line) and $\tau_\mathrm{Thomson} = 1$ (magenta line) is compared with the photospheric velocities estimated from the absorption minimum of Fe ii 5169 Å Tartaglia_2024 along with our estimates from the H$\beta$ and H$\gamma$ lines Andrews_2025.
• Figure 3: Panel (a): Rising part of the model light curve in the $r$-band overplotted on the observational data taken by Tartaglia_2024. Panel (b): The density and $^{56}$Ni distributions vs. velocity in the ejecta on day 50; magenta star indicates the photosphere location.
• Figure 4: Effects of the CSM on the light curve and the ejecta velocity. The blue line is the optimal model with the CSM and the red line is the model without the CSM. Panel (a): the density distribution for both pre-SN models; Panel (b): the corresponding bolometric light curves; Panel (c): the velocity at the photosphere as a function of time; Panel (d): the velocity distribution in the unshocked SN ejecta on day 10. The effect of the CSM on the light curve is negligible, but pronounced on the velocity of the outer layers.
• Figure 5: The evolution of the radial profiles of velocity (Panel (a)), density (Panel (b)), and gas temperature (Panel (c)) from day 1 to day 12 shows the forward shock structure and the radiative acceleration of the preshock CS gas. Profiles are plotted at the elapsed times in days indicated in Panel (a). Panel (d) shows the parameters $q$ (red line) and $Q$ (black line); colored circles correspond to the moments pointed out in Panel (a).