A detailed spectroscopic study of tidal disruption events

P. Charalampopoulos, G. Leloudas, D.B. Malesani, T. Wevers, I. Arcavi, M. Nicholl, M. Pursiainen, A. Lawrence, J.P. Anderson, S. Benetti, G. Cannizzaro, T.-W. Chen, L. Galbany, M. Gromadzki, C.P. Gutiérrez, C. Inserra, P.G. Jonker, T.E. Müller-Bravo, F. Onori, P. ShortJ. Sollerman, D.R. Young

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Abstract

Spectroscopically, tidal disruption events (TDEs) are characterized by broad (104 km s1) emission lines and show a large diversity as well as different line profiles. After carefully and consistently performing a series of data reduction tasks including host galaxy light subtraction, we present here the first detailed, spectroscopic population study of 16 optical and UV TDEs. We study a number of emission lines prominent among TDEs including Hydrogen, Helsium, and Bowen lines and we quantify their evolution with time in terms of line luminosities, velocity widths, and velocity offsets. We report a time lag between the peaks of the optical light curves and the peak luminosity of Ha spanning between 7 and 45 days. If interpreted as light echoes, these lags correspond to distances of 212-1016 cm, which are one to two orders of magnitudes larger than the estimated blackbody radii (RBB) of the same TDEs and we discuss the possible origin of this surprisingly large discrepancy. We also report time lags for the peak luminosity of the He ¯I 5876 line, which are smaller than the ones of Ha for H TDEs and similar or larger for N ¯III Bowen TDEs. We report that N ¯III Bowen TDEs have lower Ha velocity widths compared to the rest of the TDEs in our sample and we also find that a strong X-ray to optical ratio might imply weakening of the line widths. Furthermore, we study the evolution of line luminosities and ratios with respect to their radii (RBB) and temperatures (TBB). We find a linear relationship between Ha luminosity and the RBB (Lline?RBB) and potentially an inverse power-law relation with TBB (Lline TBB ß), leading to weaker Ha emission for TBB 25 000 K. The He ¯II/He ¯I ratio becomes large at the same temperatures, possibly pointing to an ionization effect. The He ¯II/Ha ratio becomes larger as the photospheric radius recedes, implying a stratified photosphere where Helium lies deeper than Hydrogen. We suggest that the large diversity of the spectroscopic features seen in TDEs along with their X-ray properties can potentially be attributed to viewing angle effects.

Original languageEnglish
Article numberA34
Number of pages30
JournalAstronomy and Astrophysics
Volume659
DOIs
Publication statusPublished - 1 Mar 2022

Bibliographical note

Acknowledgments
We thank Tom Holoien for providing us with the spectra of AT2018zr. P.C., G.L., D.B.M. and M.P. are supported by a research grant (19054) from VILLUM FONDEN. IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement number 852097), from the Israel Science Foundation (grant number 2752/19), from the United States – Israel Binational Science Foundation (BSF), and from the Israeli Council for Higher Education Alon Fellowship. M.N. is supported by a Royal Astronomical Society Research Fellowship and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948381). T.-W.C. acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. L.G. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2019 Ramón y Cajal program RYC2019-027683 and from the Spanish MICIU project PID2020-115253GA-I00. M.G. is supported by the EU Horizon 2020 research and innovation programme under grant agreement No 101004719. T.M.B. was funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113. This work is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of PESSTO/ePESSTO/ePESSTO+ (the extended Public ESO Spectroscopic Survey for Transient Objects Survey). PESSTO/ePESSTO/ePESSTO+ observations were obtained under ESO program IDs 188.D-3003, 191.D-0935, 199.D-0143, 1103.D-0328. This work is based on observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias.

Keywords

  • Black hole physics
  • Galaxy: nucleus
  • Line: formation
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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