The first systematically identified repeating partial tidal disruption event

arXiv (Cornell University)

Abstract

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 (${\sim}0.1c$) optical/UV spectral features and faint X-ray emission ($L_X \sim 3\times10^{41}$\,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.

Authors 16

1. Jean J. Somalwar

   California Institute of Technology

   Affiliation as printed

   Cahill Center for Astronomy and Astrophysics , MC 249-17 California Institute of Technology , Pasadena CA 91125 , USA

2. Vikram Ravi

   California Institute of Technology

   Affiliation as printed

   Cahill Center for Astronomy and Astrophysics , MC 249-17 California Institute of Technology , Pasadena CA 91125 , USA

3. Yuhan Yao

   University of California, Berkeley

   Affiliation as printed

   Department of Astronomy , University of California , Berkeley , CA 94720 , USA

   Miller Institute for Basic Research in Science , 468 Donner Lab , Berkeley , CA 94720 , USA

4. Muryel Guolo

   Johns Hopkins University

   Affiliation as printed

   Bloomberg Center for Physics and Astronomy , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA

5. M. J. Graham

   California Institute of Technology

   Affiliation as printed

   Cahill Center for Astronomy and Astrophysics , MC 249-17 California Institute of Technology , Pasadena CA 91125 , USA

6. Erica Hammerstein
7. Wenbin Lu

   University of California, Berkeley

   Affiliation as printed

   Department of Astronomy and Theoretical Astrophysics Center , University of California , Berkeley , CA 94720 , USA

8. M. Nicholl

   Queen's University Belfast

   Affiliation as printed

   Astrophysics Research Centre , School of Mathematics and Physics , Queens University Belfast , Belfast BT7 1NN , UK

9. Y. Sharma

   California Institute of Technology

   Affiliation as printed

   Cahill Center for Astronomy and Astrophysics , MC 249-17 California Institute of Technology , Pasadena CA 91125 , USA

10. Robert David Stein

    California Institute of Technology

    Affiliation as printed

    Cahill Center for Astronomy and Astrophysics , MC 249-17 California Institute of Technology , Pasadena CA 91125 , USA

11. Sjoert van Velzen Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory , Leiden University , Postbus 9513 , 2300 RA , Leiden , The Netherlands

12. Eric C. Bellm

    University of Washington

    Affiliation as printed

    DIRAC Institute , Department of Astronomy , University of Washington , 3910 15th Avenue NE , Seattle , WA 98195 , USA

13. M. W. Coughlin

    University of Minnesota

    Affiliation as printed

    School of Physics and Astronomy , University of Minnesota , Minneapolis , Minnesota 55455 , USA

14. Steven L. Groom

    California Institute of Technology · Infrared Processing and Analysis Center

    Affiliation as printed

    IPAC , California Institute of Technology , 1200 E. California Blvd , Pasadena , CA 91125 , USA

15. Frank J. Masci

    California Institute of Technology · Infrared Processing and Analysis Center

    Affiliation as printed

    IPAC , California Institute of Technology , 1200 E. California Blvd , Pasadena , CA 91125 , USA

16. Reed Riddle

    California Institute of Technology

    Affiliation as printed

    Caltech Optical Observatories , California Institute of Technology , Pasadena , CA 91125 , USA