AT2018fyk: Candidate Tidal Disruption Event by a (Super)Massive Black Hole Binary

The Astrophysical Journal, vol. 970, pp. 116

Abstract

Abstract The tidal disruption event (TDE) AT2018fyk has unusual X-ray, UV, and optical light curves that decay over the first ∼600 days, rebrighten, and decay again around 1200 days. We explain this behavior as a one-off TDE associated with a massive black hole (BH) binary . The sharp drop-offs from t −5/3 power laws at around 600 days naturally arise when one BH interrupts the debris fallback onto the other BH. The BH mass M • derived from fitting X-ray spectra with a slim disk accretion model and, independently, from fitting the early UV/optical light curves, is smaller by 2 orders of magnitude than predicted from the M • – σ * host galaxy relation, suggesting that the debris is accreted onto the secondary , with the fallback cut off by the primary. Furthermore, if the rebrightening were associated with the primary, it should occur around 5000 days, not the observed 1200 days. The secondary’s mass and dimensionless spin is M • , s = 2.7 − 1.5 + 0.5 × 10 5 M ⊙ and a •,s > 0.3 (X-ray spectral fitting), while the primary’s mass is M •,p = 10 7.7±0.4 M ⊙ ( M • – σ * relation). An intermediate mass BH secondary is consistent with the observed UV/optical light-curve decay, i.e., the secondary’s outer accretion disk is too faint to produce a detectable emission floor. The time of the first accretion cutoff constrains the binary separation to be (6.7 ± 1.2) × 10 −3 pc. X-ray spectral fitting and timing analyses indicate that the hard X-rays arise from a corona above the secondary’s disk. The early UV/optical emission, suggesting a super-Eddington phase for the secondary, possibly originates from shocks arising from debris circularization.

Authors 11

1. Sixiang Wen corresponding

   Radboud University Nijmegen · Chinese Academy of Sciences · National Astronomical Observatories

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

   National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People's Republic of China; wensx@bao.ac.cn

   National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People's Republic of China

2. Peter Gustaaf Jonker

   Radboud University Nijmegen

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

3. A. J. Levan

   Radboud University Nijmegen

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

4. Dongyue Li

   Chinese Academy of Sciences · National Astronomical Observatories

   Affiliation as printed

   National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People's Republic of China; wensx@bao.ac.cn

   National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People's Republic of China

5. Nicholas Chamberlain Stone

   Hebrew University of Jerusalem

   Affiliation as printed

   Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel

6. Ann I. Zabludoff

   University of Arizona

   Affiliation as printed

   University of Arizona and Steward Observatory, 933 N. Cherry Ave., Tucson, AZ 85721, USA

7. Zheng Cao Aachen Netherlands Institute for Space Research

   Radboud University Nijmegen · Space Research Organisation Netherlands

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

   SRON, Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA, Leiden, The Netherlands

8. T. Wevers

   Space Telescope Science Institute · European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile

   Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

9. Dheeraj R. Pasham

   Massachusetts Institute of Technology

   Affiliation as printed

   Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA

10. Collin Lewin

    Massachusetts Institute of Technology

    Affiliation as printed

    Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA

11. Erin Kara

    Massachusetts Institute of Technology

    Affiliation as printed

    Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA