Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers

Abstract

Progenitor models for the "luminous" subclass of Fast Blue Optical Transients (LFBOTs; prototype: AT2018cow) are challenged to simultaneously explain all of their observed properties: fast optical rise times days; peak luminosities 10 44 erg s −1 ; low yields 0.1M of 56 Ni; aspherical ejecta with a wide velocity range ( 3000 km s −1 to 0.1 − 0.5c with increasing polar latitude); presence of hydrogen-depleted-but-not-free dense circumstellar material (CSM) on radial scales from ∼ 10 14 cm to ∼ 3×10 16 cm; embedded variable source of non-thermal X-ray/γ−rays, suggestive of a compact object. We show that all of these properties are consistent with the tidal disruption and hyper-accretion of a Wolf-Rayet (WR) star by a black hole (BH) or neutron star (NS) binary companion. In contrast with related previous models, the merger occurs with a long delay following the common envelope (CE) event responsible for birthing the binary, as a result of gradual angular momentum loss to a relic circumbinary disk. Disk-wind outflows from the merger-generated accretion flow generate the 56 Nipoor aspherical ejecta with the requisite velocity range. The optical light curve is powered primarily by reprocessing X-rays from the inner accretion flow/jet, though CSM shock interaction also contributes. Primary CSM sources include WR mass-loss from the earliest stages of the merger ( 10 14 cm) and the relic CE disk and its photoevaporation-driven wind ( 10 16 cm). Longer delayed mergers may instead give rise to supernovae Type Ibn/Icn (depending on the WR evolutionary state), connecting these transient classes with LFBOTs.

Black Hole to Photosphere: 3D GRMHD Simulations of Collapsars Reveal Wobbling and Hybrid Composition Jets

“…Indeed, similar values are consistently found in all FBOTs with sufficient sensitivity for measuring the optical lightcurve to support this claim (e.g., Margutti et al 2019;Ho et al 2020). Nevertheless, the nature of FBOTs remains an open question, and additional models have been shown to explain the nature of FBOTs using different assumptions (e.g., Margutti et al 2019;Metzger 2022).…”

The Diverse Properties of Type Icn Supernovae Point to Multiple Progenitor Channels

“…Recently, Metzger (2022) proposed an alternate scenario in which the rapid evolution, multiband emission, and spectral features of SNe Ibn, SNe Icn, and AT 2018cow-like fast transients can all be reproduced by the merger of a WR star and a compact object. The differences in observed spectral features and luminosities between these classes is primarily due to the timescales on which the WR star and its compact companion merge.…”

Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova

“…This has included the ultra-bright SLSNe-I and the ultra-rapid Fast Blue Optical Transients (FBOTs), the latter having a rise time to peak of less than 10 days and a rapid fast decreasing exponential decline lasting ∼ 30 days. Recently, (Metzger 2022) discussed a peculiar and extremely rare luminous FBOT subclass (LFBOTs). There are indications that these unique phenomena are realizations along a spectrum of non-standard interactions between SN ejecta and the surrounding CSM (Kasen 2017;Leung et al 2021).…”