Modeling the fast optical transient SN 2019bkc/ATLAS19dqr with a central engine and implication for its origin

TL;DR

This paper models the fast optical transient SN 2019bkc, suggesting it results from a white dwarf-neutron star merger powered by a central engine, providing insights into its rapid evolution and origin.

Contribution

It introduces a detailed light curve model for SN 2019bkc, proposing a central engine powered explosion as its origin, which is a novel explanation for such fast transients.

Findings

SN 2019bkc's light curve is well explained by a central engine-powered ejecta.

The transient likely originates from a white dwarf-neutron star merger.

The model supports a magnetar or fallback accretion as the engine mechanism.

Abstract

Modern wide-field high-cadence surveys have revealed the significant diversity of optical transient phenomena in their luminosity and timescale distributions, which led to the discovery of some mysterious fast optical transients (FOTs). These FOTs can usually rise and decline remarkably in a timescale of a few days to weeks, which are obviously much rapider than ordinary supernovae. SN 2019bkc/ATLAS19dqr is one of the fastest detected FOTs so far and, meanwhile, it was found to be un-associated with a host galaxy. These discoveries provide a good chance to explore the possible origins of FOTs. So, we model the light curves of SN 2019bkc in details. It is found that SN 2019bkc can be well explained by the thermal emission of an explosion ejecta that is powered by a long-lasting central engine. The engine could be a spinning-down millisecond magnetar or a fallback accretion onto a compact object. Combining the engine property, the mass of the ejecta, and the hostlessness of SN 2019bkc, we suggest that this FOT is likely to originate from a merger of a white dwarf and a neutron star.