The circumstellar matter of type II intermediate luminosity optical transients (ILOTs)

TL;DR

This paper proposes that equatorial dusty disks in binary systems can obscure and re-emit the light from intermediate luminosity optical transients, explaining observations of events like N6946-BH1 and suggesting a new class of type II ILOTs.

Contribution

It introduces the concept of type II ILOTs caused by equatorial dust disks, applying AGN models to stellar outflows, and explains observational features of certain transient events.

Findings

Equatorial dusty disks can reduce observable emission by two orders of magnitude.

Most radiation escapes along polar directions, with significant attenuation at wavelengths <5μm.

The scenario explains the disappearance of star N6946-BH1 in visible light.

Abstract

I find that a 0.1-1Mo outflowing equatorial dusty disk (torus) that the binary system progenitor of an intermediate luminosity optical transient (ILOT) ejects several years to several months before and during the outburst can reduce the total emission to an equatorial observer by two orders of magnitude and shifts the emission to wavelengths of mainly >10mum. This is termed a type II ILOT (ILOT II). To reach this conclusion I use calculations of type II active galactic nuclei and apply them to the equatorial ejecta (disk/torus) of ILOTs II. This reduction in emission can last for tens of years after outburst. Most of the radiation escapes along the polar directions. The attenuation of the emission for wavelengths of <5mum can be more than three orders of magnitudes, and the emission at <2mum is negligible. Jets that the binary system launches during the outburst can collide with polar CSM and emit radiation above the equatorial plane and dust in the polar outflow can reflect emission from the central source. Therefore, during the event itself the equatorial observer might detect an ILOT. I strengthen the previously suggested ILOT II scenario to the event N6946-BH1, where a red giant star disappeared in the visible.