Properties of Thorne-Zytkow object explosions

TL;DR

This paper explores the observational signatures of Thorne-Zytkow object explosions, predicting long-duration transients with distinct luminosity and velocity features, potentially explaining some unusual supernovae.

Contribution

It provides the first detailed analysis of the observable properties and light curves of Thorne-Zytkow object explosions, highlighting their potential to be mistaken for supernovae.

Findings

Long-lasting transients with luminosity around 1e39 erg/s if accretion is short-lived.

Explosions can appear as vanished stars after a few years.

Some long-rise supernovae may be linked to Thorne-Zytkow object explosions.

Abstract

Thorne-Zytkow objects are stars that have a neutron star core with an extended hydrogen-rich envelope. Massive Thorne-Zytkow objects are proposed to explode when the nuclear reactions sustaining their structure are terminated by the exhaustion of the seed elements. In this paper, we investigate the observational properties of the possible Thorne-Zytkow object explosions. We find that Thorne-Zytkow object explosions are observed as long-duration transients lasting for several years. If the accretion disk triggering the explosions does not last for a long time, Thorne-Zytkow object explosions have a luminosity plateau with about 1e39 erg/s lasting for a few years, and then they suddenly become faint. They would be observed as vanished stars after a bright phase lasting for a few years. If the accretion disk is sustained for long time, the Thorne-Zytkow object explosions become as bright as supernovae. They would be observed as supernovae with rise times of several hundred days. We found that their photospheric velocities are 2000 km/s at most, much smaller than those found in supernovae. Supernovae with extremely long rise times such as HSC16aayt and SN 2008iy may be related to the explosions of Thorne-Zytkow objects.