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Register a new userLight Curves of Core-Collapse Supernovae with Substantial Mass Loss using the New Open-Source SuperNova Explosion Code (SNEC)
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Viktoriya Giryanskaya Morozova
Publication date
2015
fields
Physics
and research's language is
English
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We present the SuperNova Explosion Code (SNEC), an open-source Lagrangian code for the hydrodynamics and equilibrium-diffusion radiation transport in the expanding envelopes of supernovae. Given a model of a progenitor star, an explosion energy, and an amount and distribution of radioactive nickel, SNEC generates the bolometric light curve, as well as the light curves in different broad bands assuming black body emission. As a first application of SNEC, we consider the explosions of a grid of 15 Msun (at zero-age main sequence) stars whose hydrogen envelopes are stripped to different extents and at different points in their evolution. The resulting light curves exhibit plateaus with durations of ~20-100 days if >~1.5-2 Msun of hydrogen-rich material is left and no plateau if less hydrogen-rich material is left. If these shorter plateau lengths are not seen for Type IIP supernovae in nature, it suggests that, at least for zero-age main sequence masses <~ 20 Msun, hydrogen mass loss occurs as an all or nothing process. This perhaps points to the important role binary interactions play in generating the observed mass-stripped supernovae (i.e., Type Ib/c events). These light curves are also unlike what is typically seen for Type IIL supernovae, arguing that simply varying the amount of mass loss cannot explain these events. The most stripped models begin to show double-peaked light curves similar to what is often seen for Type IIb supernovae, confirming previous work that these supernovae can come from progenitors that have a small amount of hydrogen and a radius of ~500 Rsun.
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We investigate the post-explosion phase in core-collapse supernovae with 2D hydrodynamical simulations and a simple neutrino treatment. The latter allows us to perform 46 simulations and follow the evolution of the 32 successful explosions during several seconds. We present a broad study based on three progenitors (11.2 $M_odot$, 15 $M_odot$, and 27 $M_odot$), different neutrino-heating efficiencies, and various rotation rates. We show that the first seconds after shock revival determine the final explosion energy, remnant mass, and properties of ejected matter. Our results suggest that a continued mass accretion increases the explosion energy even at late times. We link the late-time mass accretion to initial conditions such as rotation strength and shock deformation at explosion time. Only some of our simulations develop a neutrino-driven wind that survives for several seconds. This indicates that neutrino-driven winds are not a standard feature expected after every successful explosion. Even if our neutrino treatment is simple, we estimate the nucleosynthesis of the exploding models for the 15 $M_odot$ progenitor after correcting the neutrino energies and luminosities to get a more realistic electron fraction.
Neutrinos are a guaranteed signal from supernova explosions in the Milky Way, and a most valuable messenger that can provide us with information about the deepest parts of supernovae. In particular, neutrinos will provide us with physical quantities, such as the radius and mass of protoneutron stars (PNS), which are the central engine of supernovae. This requires a theoretical model that connects observables such as neutrino luminosity and average energy with physical quantities. Here, we show analytic solutions for the neutrino-light curve derived from the neutrino radiation transport equation by employing the diffusion approximation and the analytic density solution of the hydrostatic equation for a PNS. The neutrino luminosity and the average energy as functions of time are explicitly presented, with dependence on PNS mass, radius, the total energy of neutrinos, surface density, and opacity. The analytic solutions provide good representations of the numerical models from a few seconds after the explosion and allow a rough estimate of these physical quantities to be made from observational data.
Core-collapse Supernovae (CCSNe) mark the deaths of stars more massive than about eight times the mass of the sun and are intrinsically the most common kind of catastrophic cosmic explosions. They can teach us about many important physical processes, such as nucleosynthesis and stellar evolution, and thus, they have been studied extensively for decades. However, many crucial questions remain unanswered, including the most basic ones regarding which kinds of massive stars achieve which kind of explosions and how. Observationally, this question is related to the open puzzles of whether CCSNe can be divided into distinct types or whether they are drawn from a population with a continuous set of properties, and of what progenitor characteristics drive the diversity of observed explosions. Recent developments in wide-field surveys and rapid-response followup facilities are helping us answer these questions by providing two new tools: (1) large statistical samples which enable population studies of the most common SNe, and reveal rare (but extremely informative) events that question our standard understanding of the explosion physics involved, and (2) observations of early SNe emission taken shortly after explosion which carries signatures of the progenitor structure and mass loss history. Future facilities will increase our capabilities and allow us to answer many open questions related to these extremely energetic phenomena of the Universe.
Recent multi-dimensional simulations of core-collapse supernovae are producing successful explosions and explosion-energy predictions. In general, the explosion-energy evolution is monotonic and relatively smooth, suggesting a possible analytic solution. We derive analytic solutions for the expansion of the gain region under the following assumptions: spherical symmetry, one-zone shell, and powered by neutrinos and $alpha$ particle recombination. We consider two hypotheses: I) explosion energy is powered by neutrinos and $alpha$ recombination, II) explosion energy is powered by neutrinos alone. Under these assumptions, we derive the fundamental dimensionless parameters and analytic scalings. For the neutrino-only hypothesis (II), the asymptotic explosion energy scales as $E_{infty} approx 1.5 M_g v_0^2 eta^{2/3}$, where $M_g$ is the gain mass, $v_0$ is the free-fall velocity at the shock, and $eta$ is a ratio of the heating and dynamical time scales. Including both neutrinos and recombination (hypothesis I), the asymptotic explosion energy is $E_{infty} approx M_g v_0^2 (1.5eta^{2/3} + beta f(rho_0))$, where $beta$ is the dimensionless recombination parameter. We use Bayesian inference to fit these analytic models to simulations. Both hypotheses fit the simulations of the lowest progenitor masses that tend to explode spherically. The fits do not prefer hypothesis I or II; however, prior investigations suggest that $alpha$ recombination is important. As expected, neither hypothesis fits the higher-mass simulations that exhibit aspherical explosions. In summary, this explosion-energy theory is consistent with the spherical explosions of low progenitor masses; the inconsistency with higher progenitor-mass simulations suggests that a theory for them must include aspherical dynamics.
Most supernova explosions accompany the death of a massive star. These explosions give birth to neutron stars and black holes and eject solar masses of heavy elements. However, determining the mechanism of explosion has been a half-century journey of great complexity. In this paper, we present our perspective of the status of this theoretical quest and the physics and astrophysics upon which its resolution seems to depend. The delayed neutrino-heating mechanism is emerging as a robust solution, but there remain many issues to address, not the least of which involves the chaos of the dynamics, before victory can unambiguously be declared. It is impossible to review in detail all aspects of this multi-faceted, more-than-half-century-long theoretical quest. Rather, we here map out the major ingredients of explosion and the emerging systematics of the observables with progenitor mass, as we currently see them. Our discussion will of necessity be speculative in parts, and many of the ideas may not survive future scrutiny. Some statements may be viewed as informed predictions concerning the numerous observables that rightly exercise astronomers witnessing and diagnosing the supernova Universe. Importantly, the same explosion in the inside, by the same mechanism, can look very different in photons, depending upon the mass and radius of the star upon explosion. A 10$^{51}$-erg (one Bethe) explosion of a red supergiant with a massive hydrogen-rich envelope, a diminished hydrogen envelope, no hydrogen envelope, and, perhaps, no hydrogen envelope or helium shell all look very different, yet might have the same core and explosion evolution.
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