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. Short; J. Sollerman; D. R. Young

doi:10.1051/0004-6361/202142122

paper

A detailed spectroscopic study of Tidal Disruption Events

arXiv:2109.00016 · doi:10.1051/0004-6361/202142122

Abstract

Spectroscopically, TDEs are characterized by broad ( 10 $^{4}$ km/s) emission lines and show 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/UV TDEs. We report a time lag between the peaks of the optical light-curves and the peak luminosity of H $α$ spanning between 7 - 45 days. If interpreted as light-echoes, these lags correspond to distances of 2 - 12 x 10 $^{16}$ cm, one to two orders of magnitudes larger than the estimated blackbody radii (R $_{BB}$ ) 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 He I $λ$ 5876 line; smaller than the ones of H $α$ for H TDEs and similar or larger for N III Bowen TDEs. We report that N III Bowen TDEs have lower H $α$ 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 (R $_{BB}$ ) and temperatures (T $_{BB}$ ). We find a linear relationship between H $α$ luminosity and the R $_{BB}$ and potentially an inverse power-law relation with T $_{BB}$ leading to weaker H $α$ emission for T $_{BB}$ $\geq$ 25000 K. The He II/He I ratio becomes large at the same temperatures possibly pointing to an ionization effect. The He II/H $α$ 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.

arXiv commentPublished in A&A (part of 2022 A&A Highlights). 31 pages (10 of the Appendix), 21 Figures

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