Common Powering Mechanism of Intermediate Luminosity Optical Transients and Luminous Blue Variables

TL;DR

This paper proposes a unified gravitational energy release mechanism in binary systems that explains both Intermediate Luminosity Optical Transients and major LBV eruptions, supported by analysis on the Energy-Time Diagram.

Contribution

It introduces a model linking ILOTs and LBV eruptions through a common binary accretion process, explaining their placement in the Optical Transient Stripe.

Findings

ILOTs and LBV eruptions occupy the Optical Transient Stripe in the ETD.

The upper boundary of the stripe is explained by high-rate accretion onto a star.

Some LBV eruptions bridge the regions of ILOTs and LBVs in the ETD.

Abstract

We study recent Intermediate Luminosity Optical Transients (ILOTs) and major eruptions of Luminous Blue Variables (LBVs), and strengthen claims for a similar mechanism powering both. This process is a short duration release of gravitational energy in a binary system. In some ILOTs a merger occurs and one of the stars does not survive the transient event, e.g., V838 Mon and V1309 Sco. In some transient events a rapid and short mass transfer process takes place and the two stars survive the transient event, e.g., the Great Eruption of Eta Carinae. We study new ILOTs and reanalyze known ones in light of new observations and models. We reach our conclusion by analyzing these ILOTs using the Energy-Time Diagram (ETD) where we plot the total energy of the eruption against its eruption timescale. ILOTs and major LBV eruptions occupy the Optical Transient Stripe (OTS) in the ETD. The upper boundary of the stripe is explained by our proposed model where a main sequence (or a slightly off-main sequence) star accretes at a very high rate (<~ 1 M_\odot yr^{-1}) from a companion. We identify one LBV, NGC 3432 OT, with two eruptions; one with weak total energy and the other with large total energy. It bridges the regions of the ILOTs and LBVs in the OTS. We further study the ILOT M85 OT2006 and show that it cannot be a nova, even not an extreme one. We build a model where ILOTs can become optically thin in a timescale of few years and the inflated envelope collapses into an accretion disk around the star. Such an ILOT will evolve blue-ward after few years.