Black hole emergence in supernovae

If a black hole formed in a core-collapse supernova is accreting material from the base of the envelope, the accretion luminosity could be observable in the supernova light curve. Here we continue the study of matter fallback onto a black hole in the wake of a supernova and examine realistic supernovae models that allow for an early emergence of the accretion luminosity. Such cases may provide a direct observational identification of the black hole formed in the aftermath of the explosion. Our approach combines analytic estimates and fully relativistic, radiation-hydrodynamic numerical computations. We employ a numerical hydrodynamical scaling technique to accommodate the diverse range of dynamical timescales in a single simulation. We find that while in typical Type II supernovae heating by radioactive decays dominates the late-time light curve, low-energy explosions of more massive stars should provide an important exception where the accretion luminosity will emerge while it is still relatively large. Our main focus is on the only current candidate for such an observation, the very unusual SN 1997D. Owing to the low energy of the explosion and the very small (2 × 10^-3 M_⊙) inferred mass of ⁵⁶Co in the ejected envelope, we find that accretion should become the dominant source of its luminosity during the year 2000. The total luminosity at emergence is expected to lie in the range 0.5-3 × 10³⁶ ergs s^-1, potentially detectable with the Hubble Space Telescope. We also discuss the more favorable case of explosions that eject negligible amounts of radioactive isotopes and find that the black hole is likely to emerge a few tens of days after the explosion, with a luminosity of ∼10³⁷ ergs s^-1.