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Title: “Super-kilonovae” from Massive Collapsars as Signatures of Black Hole Birth in the Pair-instability Mass Gap

The core collapse of rapidly rotating massive ∼ 10Mstars (“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 ofr-process nucleosynthesis. Here, we explore the signatures of collapsars from progenitors with helium cores ≳ 130Mabove 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 ≳ 5–10Minr-process elements and ∼ 0.1–1Mof56Ni, expanding at velocities ∼0.1 c. Radioactive heating of the disk wind ejecta powers an optical/IR transient, with a characteristic luminosity ∼ 1042erg s−1and 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”).

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Author(s) / Creator(s):
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Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Page Range / eLocation ID:
Article No. 100
Medium: X
Sponsoring Org:
National Science Foundation
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