Double tidal disruption events or repeating partial tidal disruption events in AT 2020vdq

TL;DR

This paper analyzes AT 2020vdq to determine if its two flares are due to repeating partial tidal disruption events, concluding that the evidence favors two separate TDEs rather than a repeating partial TDE scenario.

Contribution

A simplified method is proposed to test the repeating pTDEs scenario by comparing stellar masses derived from theoretical models for two flares.

Findings

The stellar masses for the two flares are approximately 2 and 0.36 solar masses.

The large mass difference challenges the repeating pTDEs scenario for AT 2020vdq.

Results suggest two separate TDEs are more likely than a repeating partial TDE.

Abstract

AT 2020vdq has been known as a candidate of repeating partial tidal disruption events (pTDEs), due to its two flares with a time interval of $\sim$1000 days. Here, a simplified method is proposed to test such repeating pTDEs scenario considering a main-sequence star tidally disrupted twice. For the two flares in AT 2020vdq if related to the repeating pTDEs scenario, theoretical TDE model determined stellar mass of the original star disrupted for the first flare should be not very different from the mass of the star (to trace the reminder of the original star) disrupted for the second flare, because a partial TDE with impact parameter $\beta$ smaller than 1 can lead to most of (probable higher than 90\%) the stellar mass also bound to the reminder of the original star. After considering theoretical TDE model applied to describe the two flares in AT 2020vdq, the model determined stellar masses are about 2${\rm M_\odot}$ and $0.36{\rm M_\odot}$ for the stars disrupted in the first flare and the second flare. The large mass difference cannot be reasonably expected by the repeating pTDEs with $\beta$ around 0.6 in AT 2020vdq. The results in this manuscript indicate that the repeating pTDEs scenario is not preferred at current stage in AT 2020vdq, but the probable double TDEs for two individual stars tidally disrupted should be currently recommended.