"Super-kilonovae" from Massive Collapsars as Signatures of Black Hole Birth in the Pair-instability Mass Gap
Abstract
The core collapse of rapidly rotating massive ~ 10M ⊙ stars ("collapsars"), and the resulting formation of hyperaccreting black holes, comprise a leading model for the central engines of long-duration gamma-ray bursts (GRBs) and promising sources of r-process nucleosynthesis. Here, we explore the signatures of collapsars from progenitors with helium cores ≳ 130M ⊙ above the pair-instability mass gap. While the rapid collapse to a black hole likely precludes prompt explosions in these systems, we demonstrate that disk outflows can generate a large quantity (up to ≳ 50M ⊙) of ejecta, comprised of ≳ 5-10M ⊙ in r-process elements and ~ 0.1-1M ⊙ of 56Ni, expanding at velocities ~0.1 c. Radioactive heating of the disk wind ejecta powers an optical/IR transient, with a characteristic luminosity ~ 1042 erg s-1 and a spectral peak in the near-IR (due to the high optical/UV opacities of lanthanide elements), similar to kilonovae from neutron star mergers, but with longer durations ≳1 month. These "super-kilonovae" (superKNe) herald the birth of massive black holes ≳ 60M ⊙, which-as a result of disk wind mass loss-can populate the pair-instability mass gap "from above," and could potentially create the binary components of GW190521. SuperKNe could be discovered via wide-field surveys, such as those planned with the Roman Space Telescope, or via late-time IR follow-up observations of extremely energetic GRBs. Multiband gravitational waves of ~ 0.1-50 Hz from nonaxisymmetric instabilities in self-gravitating massive collapsar disks are potentially detectable by proposed observatories out to hundreds of Mpc; in contrast to the "chirp" from binary mergers, the collapsar gravitational-wave signal decreases in frequency as the disk radius grows ("sad trombone").
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2022
- DOI:
- 10.3847/1538-4357/ac8d04
- arXiv:
- arXiv:2111.03094
- Bibcode:
- 2022ApJ...941..100S
- Keywords:
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- Astrophysical black holes;
- Stellar mass black holes;
- High energy astrophysics;
- Gravitational waves;
- Gravitational wave sources;
- Late stellar evolution;
- Stellar evolution;
- Gamma-ray bursts;
- Core-collapse supernovae;
- Gravitational collapse;
- Transient sources;
- Time domain astronomy;
- 98;
- 1611;
- 739;
- 678;
- 677;
- 911;
- 1599;
- 629;
- 304;
- 662;
- 1851;
- 2109;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics;
- General Relativity and Quantum Cosmology
- E-Print:
- 36 pages, 21 figures, 2 tables