Parameterisations of thermal bomb explosions for core-collapse supernovae and 56Ni production

TL;DR

This paper shows that including the initial stellar core collapse in thermal bomb models of supernovae alters nickel production results, challenging previous conclusions about explosion timescales and mechanisms.

Contribution

It introduces a revised thermal bomb setup that accounts for core collapse, demonstrating its impact on nucleosynthesis predictions and the interpretation of supernova explosion mechanisms.

Findings

Including core collapse changes Ni-56 yield dependence on explosion timescale.

Slower explosions can produce more Ni-56 when collapse is modeled.

The choice of mass cut influences Ni-56 production more than energy deposition volume.

Abstract

Thermal bombs are a widely used method to artificially trigger explosions of core-collapse supernovae (CCSNe) to determine their nucleosynthesis or ejecta and remnant properties. Recently, their use in spherically symmetric (1D) hydrodynamic simulations led to the result that {56,57}Ni and 44Ti are massively underproduced compared to observational estimates for Supernova 1987A, if the explosions are slow, i.e., if the explosion mechanism of CCSNe releases the explosion energy on long timescales. It was concluded that rapid explosions are required to match observed abundances, i.e., the explosion mechanism must provide the CCSN energy nearly instantaneously on timescales of some ten to order 100 ms. This result, if valid, would disfavor the neutrino-heating mechanism, which releases the CCSN energy on timescales of seconds. Here, we demonstrate by 1D hydrodynamic simulations and nucleosynthetic post-processing that these conclusions are a consequence of disregarding the initial collapse of the stellar core in the thermal-bomb modelling before the bomb releases the explosion energy. We demonstrate that the anti-correlation of 56Ni yield and energy-injection timescale vanishes when the initial collapse is included and that it can even be reversed, i.e., more 56Ni is made by slower explosions, when the collapse proceeds to small radii similar to those where neutrino heating takes place in CCSNe. We also show that the 56Ni production in thermal-bomb explosions is sensitive to the chosen mass cut and that a fixed mass layer or fixed volume for the energy deposition cause only secondary differences. Moreover, we propose a most appropriate setup for thermal bombs.