text: 179,104,1457525905711042570,901266828655284225,Brian Metzger,"<LINK> Perfect timing for new paper on a new type of transient. Punchline: while kilonovae signal the birth of light black holes (from NS mergers), ""Super-kilonovae"" may accompany the birth of the most massive (stellar mass) LIGO BHs. @astroVAV @amanagarawal20 Basic idea: scale up collapsars (progenitors of long GRBs) to extremely massive stars above the pair-instability mass gap. When trying to feed a newly formed BH at such high rates, much of the in-falling star doesn't make it in, instead being ejected in accretion disk outflows. We estimate these neutron-rich outflows generate r-process elements, with yields ~10s of Msun (~100 times higher than in neutron star mergers like GW170817 and ~10 times higher than ""ordinary"" low-mass collapsars). This results in a lower final mass BH than one would predict from the progenitor He core, allowing to fill-in the pair-instability mass-gap ""from above,"" and providing a speculative channel for generating massive BBH like the components GW190521. <LINK> This large mass ejection powers a radioactively-powered transient much brighter and longer-lasting than ordinary kilonovae, similar to SNe but much redder (near-IR peak); hence ""Super-kilonova"". Roman Space Telescope could potentially discover these transients out to z ~ 1. <LINK> The nominal BH accretion rates achieved are also significantly higher than ordinary collapsars, allowing to power particularly energetic gamma-ray bursts. SuperKN should be searched for following the most energetic GRBs by JWST. Gravitational instabilities in these massive disks could also generate GW emission accessible to 3G detectors; unlike in the ""chirp"" in CO mergers, the GW signal decreases in frequency with time as the disk grows in radius (we term ""sad trombone"", to borrow a term from the FRBs). <LINK> Overall a fun ""ideas"" paper to work out, which puts together some ideas already germinating out there in the community, and completed by a talented group of young researchers, most of which overlapped here at Columbia/CCA over past few years.",https://arxiv.org/abs/2111.03094,"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""). ","""Super-Kilonovae"" from Massive Collapsars as Signatures of Black-Hole