[Paper Review] Nucleosynthesis Calculations from Core-Collapse Supernovae

Chris L. Fryer, Patrick Young+9 more|ArXiv.org|Nov 28, 2008

Gamma-ray bursts and supernovae11 references3 citations

TL;DR

This paper evaluates explosion mechanisms in core-collapse supernova nucleosynthesis simulations, advocating for entropy or energy injection over piston-driven models to accurately reproduce fallback and yields. It finds piston-driven models severely underestimate fallback, leading to order-of-magnitude errors in heavy-element yields, while energy/entropy injection better matches the convection-enhanced neutrino-driven mechanism and is now the standard in the NuGrid collaboration for yield accuracy within a factor of a few.

ABSTRACT

We review some of the uncertainties in calculating nucleosynthetic yields, focusing on the explosion mechanism. Current yield calculations tend to either use a piston, energy injection, or enhancement of neutrino opacities to drive an explosion. We show that the energy injection, or more accurately, an entropy injection mechanism is best-suited to mimic our current understanding of the convection-enhanced supernova engine. The enhanced neutrino-opacity technique is in qualitative disagreement with simulations of core-collapse supernovae and will likely produce errors in the yields. But piston-driven explosions are the most discrepant. Piston-driven explosion severely underestimate the amount of fallback, leading to order-of-magnitude errors in the yields of heavy elements. To obtain yields accurate to the factor of a few level, we must use entropy or energy injection and this has become the NuGrid collaboration approach.

Motivation & Objective

• To assess the accuracy of different artificial explosion mechanisms in core-collapse supernova nucleosynthesis calculations.
• To identify which explosion method best reproduces the convection-enhanced neutrino-driven explosion mechanism observed in 3D simulations.
• To reduce systematic errors in nucleosynthetic yields, particularly for heavy elements like 56Ni and 44Ti, by correcting for fallback overestimation in piston models.
• To establish a more physically consistent framework for yield calculations using entropy or energy injection, adopted by the NuGrid collaboration.

Proposed method

• Uses 3D supernova simulation data to model energy deposition in the convective region around the proto-neutron star, focusing on entropy and energy injection profiles.
• Applies entropy injection to maintain a uniform entropy gradient across the convective region as it expands, mimicking the physical behavior seen in convection-enhanced explosions.
• Implements energy injection limited to the convective region (a few tenths of a solar mass), avoiding energy deposition beyond the shock front.
• Compares results from piston-driven, energy-injected, and enhanced-neutrino-opacity models to assess their impact on fallback and nucleosynthetic yields.
• Sets a cutoff for energy injection when the shock radius exceeds 1000 km, allowing natural decline in energy deposition as density drops.
• Calibrates injection rate and total energy to constrain delay time and reduce yield uncertainties to within a factor of a few.

Experimental results

Research questions

• RQ1 How do different artificial explosion mechanisms—piston, energy injection, and enhanced neutrino opacity—affect nucleosynthetic yields in core-collapse supernovae?
• RQ2 To what extent do piston-driven models underestimate fallback, and what is the resulting impact on heavy-element yields?
• RQ3 Can entropy or energy injection mechanisms reproduce the physical conditions of the convection-enhanced neutrino-driven explosion mechanism more accurately than piston models?
• RQ4 How do variations in energy injection rate and total energy affect the final nucleosynthetic yields, and can these be constrained to reduce uncertainty?
• RQ5 What is the role of fallback in reconciling supernova models with observed compact remnant masses and r-process nucleosynthesis?

Key findings

• Piston-driven explosions severely underestimate fallback, leading to order-of-magnitude errors in yields of heavy elements such as 56Ni and 44Ti.
• Energy injection and entropy injection mechanisms produce yields consistent with the convection-enhanced neutrino-driven explosion mechanism, while enhanced neutrino-opacity models are in qualitative disagreement with 3D simulations.
• The 23e-series piston model produces a 2.6 M⊙ remnant at ~2×10^51 erg explosion energy, whereas other models (WW and CL) predict remnant masses below 1.5 M⊙, highlighting the artificial nature of piston-driven fallback.
• Piston models overproduce elements like 45Sc by more than a factor of 10 compared to energy-injected models, indicating significant yield discrepancies.
• The 44Ti/56Ni yield ratio can vary by an order of magnitude between piston and energy-injected models, affecting interpretations of historical supernovae like Cassiopeia A.
• The NuGrid collaboration now uses entropy injection to achieve yield accuracy within a factor of a few, with injection stopped when the shock radius exceeds 1000 km.