2025MNRAS.538..572S

We present a set of eight fallback simulations of zero-metallicity progenitors with masses between $60 \, \mathrm{M}_\odot$ and $95 \, \mathrm{M}_\odot$. The simulations are computed in 2D with the general relativistic COCONUT-FMT code for the first few seconds after black hole formation, and then mapped to the Newtonian code PROMETHEUS for long-duration simulations to shock breakout. All simulations produce successful explosions with final energies ranging from $0.41\times 10^{51}\, $ to $2.5 \times 10^{51}\, \mathrm{erg}$ and black hole masses from $20.7 \, \mathrm{M}_\odot$ to $34.4 \, \mathrm{M}_\odot$. Explosion energies and remnant masses do not vary monotonically with progenitor mass, but the mass cuts cluster near the outer edge of the helium core. A supplementary model with decreased neutrino heating provides a tentative indication that successful explosions require the shock to reach the sonic point in the infall profile by the time of black hole formation. The propagation of the shock to the surface is only approximately captured by proposed shock invariants, but these may still be sufficient to extrapolate the final black hole mass from the first seconds of evolution. We also discuss potential multimessenger signatures of the predicted fallback explosions. The enrichment of the ejecta in intermediate mass and iron-group elements varies considerably and is non-negligible for the more powerful explosions. Low-level neutrino emission after black hole formation from these very massive progenitors may be detectable in the case of a Galactic event.