{
  "id": "2111.03094",
  "version": "v1",
  "published": "2021-11-04T18:21:01.000Z",
  "updated": "2021-11-04T18:21:01.000Z",
  "title": "\"Super-Kilonovae\" from Massive Collapsars as Signatures of Black-Hole Birth in the Pair-instability Mass Gap",
  "authors": [
    "Daniel M. Siegel",
    "Aman Agarwal",
    "Jennifer Barnes",
    "Brian D. Metzger",
    "Mathieu Renzo",
    "V. Ashley Villar"
  ],
  "comment": "36 pages, 21 figures, 2 tables",
  "categories": [
    "astro-ph.HE",
    "astro-ph.SR",
    "gr-qc"
  ],
  "abstract": "The core collapse of rapidly rotating massive ~10 Msun stars (\"collapsars\"), and resulting formation of hyper-accreting black holes, are a leading model for the central engines of long-duration gamma-ray bursts (GRB) and promising sources of r-process nucleosynthesis. Here, we explore the signatures of collapsars from progenitors with extremely massive helium cores >130 Msun above the pair-instability mass gap. While rapid collapse to a black hole likely precludes a prompt explosion in these systems, we demonstrate that disk outflows can generate a large quantity (up to >50 Msun) of ejecta, comprised of >5-10 Msun in r-process elements and ~0.1-1 Msun of $^{56}$Ni, expanding at velocities ~0.1c. Radioactive heating of the disk-wind ejecta powers an optical/infrared transient, with a characteristic luminosity $\\sim 10^{42}$ erg s$^{-1}$ and spectral peak in the near-infrared (due to the high optical/UV opacities of lanthanide elements) similar to kilonovae from neutron star mergers, but with longer durations $\\gtrsim$ 1 month. These \"super-kilonovae\" (superKNe) herald the birth of massive black holes >60 Msun, 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 infrared follow-up observations of extremely energetic GRBs. Gravitational waves of frequency ~0.1-50 Hz from non-axisymmetric instabilities in self-gravitating massive collapsar disks are potentially detectable by proposed third-generation intermediate and high-frequency observatories at distances up 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\").",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-11-04T18:21:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "pair-instability mass gap",
      "massive collapsar",
      "black-hole birth",
      "black hole",
      "super-kilonovae"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 36,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}