Type II intermediate-luminosity optical transients (ILOTs)

TL;DR

This paper suggests that some intermediate-luminosity optical transients are obscured by equatorial ejecta in binary systems, causing them to appear only in infrared for years, and possibly explaining the disappearance of certain red giants.

Contribution

It introduces a new model where equatorial ejecta in binary systems cause transient obscuration, offering an alternative explanation for observed stellar disappearances.

Findings

Obscuration by equatorial ejecta can hide central sources for years.

The model explains the disappearance of N6946-BH1 as a type II ILOT.

Predicted reappearance in visible band in several decades.

Abstract

We propose that in a small fraction of intermediate luminosity optical transients (ILOTs) powered by a strongly interacting binary system, the ejected mass in the equatorial plane can block the central source from our line of sight. We can therefore observe only radiation that is reprocessed by polar outflow, much as in type~II active galactic nuclei (AGN). An ejection of $M_{\rm ej,e}=10^{-4} ~\rm{M_\odot} ~ (1 ~\rm{M_\odot})$ at 30 degrees from the equatorial plane and at a velocity of $v_{\rm e} = 100 ~\rm{km~s^{-1}}$ will block the central source in the NIR for about 5 years (500 years). During that period of time the object might disappear in the visible band, and be detected only in the IR band due to polar dust. We raise the possibility that the recently observed disappearance of a red giant in the visible, designated N6946-BH1, is a type~II ILOT rather than a failed supernova. For this case we estimate that the ejected mass in the polar direction was $M_{\rm ej,p}\approx 10^{-3} ~\rm{M_\odot}$. Our scenario predicts that this event should reinstate its visible emission in several decades.