Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk

Research output: Contribution to journalArticle


  • T. Wevers
  • D. R. Pasham
  • S. van Velzen
  • G. Leloudas
  • S. Schulze
  • J. C. A. Miller-Jones
  • P. G. Jonker
  • M. Gromadzki
  • E. Kankare
  • S. T. Hodgkin
  • L. Wyrzykowski
  • Z. Kostrzewa-Rutkowska
  • S. Moran
  • M. Berton
  • K. Maguire
  • F. Onori
  • S. Mattila
  • M. Nicholl

Research units

  • Univ Cambridge, University of Cambridge, Inst Astron
  • MIT, Massachusetts Institute of Technology (MIT), Kavli Inst Astrophys & Space Res
  • NYU, New York University, Ctr Cosmol & Particle Phys
  • Tech Univ Denmark, Technical University of Denmark, Natl Space Inst, DTU Space
  • Weizmann Inst Sci, Weizmann Institute of Science, Dept Particle Phys & Astrophys
  • Curtin Univ, Curtin University, ICRAR
  • Radboud Univ Nijmegen, Radboud University Nijmegen, Dept Astrophys, IMAPP
  • Warsaw Univ, University of Warsaw, Astron Observ
  • University of Turku
  • SRON, Netherlands Inst Space Res
  • Nordic Opt Telescope
  • Trinity Coll Dublin, Trinity College Dublin, Sch Phys
  • Ist Astrofis & Planetol Spaziali INAF, Istituto Nazionale Astrofisica
  • Univ Birmingham, University of Birmingham, Sch Phys & Astron
  • Finnish Centre for Astronomy with ESO (FINCA)


We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN-18ul discovered by ASAS-SN. The Swift light curve is atypical for a TDE, entering a plateau after similar to 40d of decline from peak. After 80d the UV/optical light curve breaks again to decline further, while the X-ray emission becomes brighter and harder. In addition to broad H, He, and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase. We identify both high-ionization (Oiii) and low-ionization (Feii) lines, which are visible for similar to 45d. We similarly identify Feii lines in optical spectra of ASASSN-15oi 330 d after discovery, indicating that a class of Fe-rich TDEs exists. The spectral similarity between AT 2018fyk, narrow-line Seyfert 1 galaxies, and some extreme coronal line emitters suggests that TDEs are capable of creating similar physical conditions in the nuclei of galaxies. The Feii lines can be associated with the formation of a compact accretion disc, as the emergence of low-ionization emission lines requires optically thick, high-density gas. Taken together with the plateau in X-ray and UV/optical luminosity this indicates that emission from the central source is efficiently reprocessed into UV/optical wavelengths. Such a two-component light curve is very similar to that seen in the TDE candidate ASASSN-15lh, and is a natural consequence of a relativistic orbital pericentre.


Original languageEnglish
Pages (from-to)4816-4830
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Oct 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • accretion, accretion discs, black hole physics, galaxies: nuclei, ultraviolet: galaxies, X-rays: galaxies, FE-II EMISSION, BLACK-HOLE MASSES, ACCRETION DISC, FOLLOW-UP, GALAXIES, STELLAR, POPULATION, STARS, LINES, SPECTROSCOPY

ID: 37150142