# Fates of Rotating Supergiants from Stellar Mergers and the Landscape of Transients upon Core-collapse

## TL;DR

This study models rotating supergiants from binary mergers to understand their evolution and explosion outcomes, linking them to specific supernova types, gamma-ray bursts, and luminous transients.

## Contribution

It provides a detailed grid of post-merger stellar models with rotation, exploring their core-collapse behavior and associated transient phenomena, a novel approach to merger product evolution.

## Key findings

- Merger mass gain influences supergiant type (blue vs. red).
- Rotating BSGs can produce SN 1987A-like supernovae.
- Failed explosions lead to fallback accretion and potential jets.

## Abstract

We present a grid of rotating supergiant models from post-main sequence binary merger products, constructed by the MESA stellar evolution code. We focus on the evolution of these stars until core-collapse, in addition to their rotation, which could influence their mass loss and explosion phenomenology. We find that (i) as in previous studies, larger mass gain by merger favors the production of blue supergiants (BSGs) over red supergiants, and (ii) merger products that end as BSGs at core collapse have rotating outer envelopes, with lower-mass BSGs having faster envelope rotation due to less wind mass loss. We model the expected transients from these BSGs upon core-collapse, considering cases where the neutrino-driven explosion is successful and unsuccessful. The successful explosions result in supernovae (SNe) with long-rising light curves of morphology similar to SN 1987A. Failed explosions of these BSGs result in envelope fallback of $\sim (0.1$- several) $~M_\odot$ over $10^3$-$10^5$ seconds that power strong ($10^{51}$-$10^{53}$ erg) accretion-driven outflows in winds and possibly jets, with relativistic jets (if formed) generally capable of breaking out of the BSG envelope. Our modeling points to these merger-origin BSGs as viable progenitors for SN 1987A-like SNe, ultra-long gamma-ray bursts, and some of the fast luminous transients found in high-cadence optical surveys.