Supernovae Shock Breakout from Red Supergiants in Two Dimensions

TL;DR

This work advances shock-breakout modeling by performing 2D multigroup radiation-hydrodynamics simulations of red supergiant explosions using CASTRO, with 20 and 25 $M_\odot$ progenitors mapped from 1D FLASH models and surrounded by wind-driven CSM. The simulations reveal strong radiation precursors that drive instabilities and push the photosphere outward before breakout, producing UV-dominated peak luminosities of about $10^{44}$ erg s$^{-1}$ with $\mathrm{FWHM}\sim1$–$3$ h; the breakout is longer and dimmer than for blue supergiants, and the color evolves blue-to-red after the peak. Dense CSM increases photon diffusion, lengthens rise times by a few hours, and reduces peak luminosity by ~50%, illustrating the crucial role of the environment in shaping observables. The 2D results align better with observed breakout signatures than prior 1D models, implying milder pre-explosion mass loss than previously inferred and highlighting how RSG atmospheres and CSM histories imprint the earliest SN signals.

Abstract

We present new two-dimensional radiation hydrodynamic simulations of supernova shock breakout from red supergiants using the $\texttt{CASTRO}$ code. Our progenitors are 20 and 25 M$_{\odot}$ solar-metallicity stars evolved from the zero-age main sequence with $\texttt{MESA}$ and exploded in one dimension using $\texttt{FLASH}$. We consider a range of circumstellar media (CSM) produced by stellar winds to investigate how pre-explosion mass-loss affects shock breakout. The multigroup flux-limited diffusion scheme in $\texttt{CASTRO}$ captures the interaction between the explosion shock, its radiation precursor, and the surrounding CSM. We find that strong radiation precursors, generated by radiation leakage behind the shock, can drive fluid instabilities and move the effective photosphere outward before the shock reaches the stellar surface. The resulting breakout emissions reach peak luminosities of ${\sim}10^{44}$ erg s$^{-1}$ with full-width half-maximum durations of 1-3 hr, which are much dimmer and longer than those from blue supergiants. The light-curve colors gradually evolve from blue to red after the peak. The 25 M$_{\odot}$ model with explosion energy $E \sim 1.69\times10^{51}$ erg produces ${\sim}$10-30\% higher maximum luminosity than the 20 M$_{\odot}$ model with $E \sim 1.09\times10^{51}$ erg. The dense CSM further extends the breakout rise time by increasing the photon diffusion. These results provide new constraints on red supergiant atmospheres and mass-loss histories prior to core collapse.

Figures (8)

• Figure 1: 1D density and radial velocity profiles for R20 and R25 when the shock reaches the hydrogen envelope. At this moment, the corresponding shock velocity is $v=6.35\times 10^{8}$$\mathrm{cm}\,\mathrm{s}^{-1}$ for R20 and $v=6.8\times 10^{8}$$\mathrm{cm}\,\mathrm{s}^{-1}$ for R25. The original stellar radii of R20 and R25 are $R_{\rm *}=7.6\times 10^{13}$ cm and $R_{\rm *}=8.3\times 10^{13}$ cm, respectively.
• Figure 2: The snapshot of gas and radiation energy densities before the shock reaches the stellar surface for R20. Cyan and red vectors represent the velocity and radiation flux, respectively. The pink dashed line indicates the location of the photosphere. Rayleigh–Taylor fingers emerge around the contact discontinuity near ${\sim}4\times10^{13}$ cm. The atmosphere expands with a velocity that is negligible compared to the shock velocity.
• Figure 3: The evolution of the shock breakout for R20, R20T, R25, and R25T shown in each row. Each column, from left to right, represents breakout phases at pre-breakout, maximum luminosity, and post-breakout. The pink dashed line marks the photosphere. In general, the stellar surface remains intact, but RT instabilities have developed within the envelope at the pre-breakout phase. When the breakout occurs and its emission reaches its peak, the velocity contour shows large velocity fluctuations in the CSM, indicating the RPS has started to develop and affects the locations of the photosphere. Some of the CSM can be accelerated by the radiation up to $v{\sim} 10^{10}$$\mathrm{cm}\,\mathrm{s}^{-1}$ in R20 and R25 but $v{\sim}10^9$$\mathrm{cm}\,\mathrm{s}^{-1}$ in R20T and R25T. The dense CSM can enlarge the radius of the photosphere and delay the timing of shock breakout.
• Figure 4: Evolution of the 1D density, velocity, and temperature profiles for R20 (left) and R25 (right) based on viewing angles of $15^\circ$ (dotted), $60^\circ$ (dashed), and angle-averaged (solid). Colors indicate key epochs: ${\sim}$30 hr pre-maximum luminosity (blue), ${\sim}$2 hr pre-maximum (orange), maximum luminosity (green), and post-breakout (red). As time evolves, angle-dependent profiles start to deviate significantly due to the developing RPS that causes large fluctuations in velocity and temperature of the CSM.
• Figure 5: Evolution of the 1D density, velocity, and temperature profiles for R20T (left) and R25T (right) based on viewing angles of $15^\circ$ (dotted), $60^\circ$ (dashed), and angle-averaged (solid). Colors indicate key epochs: ${\sim}$30 hr pre-maximum luminosity (blue), ${\sim}$2 hr pre-maximum (orange), maximum luminosity (green), and post-breakout (red). Similar to Figure \ref{['fig:4']}, as time evolves, angle-dependent profiles start to deviate more due to the developing RPS that causes large fluctuations in velocity and temperatures of CSM. However, the amount of deviations in angle-dependent profiles of R20T/ R25T is less than that of R20/ R25 due to the dense CSM.