2023/10/05 by Somalwar, Jean J., Ravi, Vikram, Yao, Yuhan +13 · 5 citations
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2310.03782
Tidal disruption events (TDEs) occur when a star enters the tidal radius of a supermassive black hole (SMBH). If the star only grazes the tidal radius, a fraction of the stellar mass will be accreted in a partial TDE (pTDE). The remainder can continue orbiting and may re-disrupted at pericenter, causing a repeating pTDE. pTDEs may be as or more common than full TDEs (fTDEs), yet few are known. In this work, we present the discovery of the first repeating pTDE from a systematically-selected sample, AT 2020vdq. AT 2020vdq was originally identified as an optically- and radio-flaring TDE. Around 3 years after its discovery, it rebrightened dramatically and rapidly in the optical. The optical flare was remarkably fast and luminous compared to previous TDEs. It was accompanied by extremely broad (∼0.1c) optical/UV spectral features and faint X-ray emission (LX ∼ 3×1041 erg s-1), but no new radio-emitting component. Based on the transient optical/UV spectral features and the broadband light curve, we show that AT 2020vdq is a repeating pTDE. We then use it to constrain TDE models; in particular, we favor a star originally in a very tight binary system that is tidally broken apart by the Hills mechanism. We also constrain the repeating pTDE rate to be 10-6 to 10-5 yr-1 galaxy-1, with uncertainties dominated by the unknown distribution of pTDE repeat timescales. In the Hills framework, this means the binary fraction in the galactic nucleus is of the order few percent.