1. Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk
- Author
-
Matt Nicholl, Marco Berton, Erkki Kankare, Mariusz Gromadzki, S. van Velzen, James Miller-Jones, Giorgos Leloudas, Z. Kostrzewa-Rutkowska, Łukasz Wyrzykowski, S. Moran, Francesca Onori, Peter G. Jonker, Simon Hodgkin, Kate Maguire, Seppo Mattila, Steve Schulze, Dheeraj R. Pasham, Thomas Wevers, University of Cambridge, Massachusetts Institute of Technology, University of Maryland, Baltimore, Technical University of Denmark, Weizmann Institute of Science, Curtin University, SRON Netherlands Institute for Space Research, Warsaw University, University of Turku, Metsähovi Radio Observatory, Trinity College Dublin, Istituto di Astrofisica e Planetologia Spaziali, University of Edinburgh, Aalto-yliopisto, and Aalto University
- Subjects
010504 meteorology & atmospheric sciences ,Astronomy ,Astrophysics::High Energy Astrophysical Phenomena ,Population ,black hole physics ,Doubly ionized oxygen ,nuclei [galaxies] ,FOS: Physical sciences ,LINES ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Luminosity ,accretion ,0103 physical sciences ,Emission spectrum ,education ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,POPULATION ,0105 earth and related environmental sciences ,Line (formation) ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,education.field_of_study ,SPECTROSCOPY ,Accretion (meteorology) ,BLACK-HOLE MASSES ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,accretion discs ,Galaxy ,galaxies [X-rays] ,GALAXIES ,Stars ,FE-II EMISSION ,STELLAR ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,galaxies [ultraviolet] ,Astrophysics - High Energy Astrophysical Phenomena ,FOLLOW-UP ,ACCRETION DISC ,STARS - Abstract
We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) AT 2018fyk/ASASSN-18ul discovered by ASAS-SN. The Swift lightcurve is atypical for a TDE, entering a plateau after $\sim$40 days of decline from peak. After 80 days the UV/optical lightcurve 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 ionisation (O III) and low ionisation (Fe II) lines, which are visible for $\sim$45 days. We similarly identify Fe II 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 Fe II lines can be associated with the formation of a compact accretion disk, as the emergence of low ionisation 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 lightcurve is very similar to that seen in the TDE candidate ASASSN-15lh, and is a natural consequence of a highly relativistic orbital pericenter., Version accepted for publication in MNRAS
- Published
- 2019
- Full Text
- View/download PDF