Reverberation in Tidal Disruption Events: Dust Echoes, Coronal Emission Lines, Multi-wavelength Cross-correlations, and QPOs

Abstract

Stellar tidal disruption events (TDEs) are typically discovered by transient emission due to accretion or shocks of the stellar debris. Yet this luminous flare can be reprocessed by gas or dust that inhabits a galactic nucleus, resulting in multiple reverberation signals. Nuclear dust heated by the TDE will lead to an echo at infrared wavelengths (1-10 μm) and transient coronal lines in optical spectra of TDEs trace reverberation by gas that orbits the black hole. Both of these signal have been detected, here we review this rapidly developing field. We also review the results that have been extracted from TDEs with high-quality X-ray light curves: quasi periodic oscillations (QPOs), reverberation lags of fluorescence lines, and cross-correlations with emission at other wavelengths. The observational techniques that are covered in this review probe the emission from TDEs over a wide range of scales: from $\sim 1$ ∼ 1 light year to the innermost parts of the newly formed accretion disk. They provide insights into important properties of TDEs such as their bolometric output and the geometry of the accretion flow. While reverberation signals are not detected for every TDE, we anticipate they will become more commonplace when the next generation of X-ray and infrared instruments become operational.

Systematic light curve modelling of TDEs: statistical differences between the spectroscopic classes

“…• TDE-H also have significantly larger photospheric radii, consistent with results from van Velzen et al (2021a), Charalampopoulos et al (2021), andHinkle et al (2020) • TDE-H+He show moderate evidence for more massive SMBHs on average…”

“…et al (2014), 2: Hinkle et al (2021), 3: Holoien et al (2016a), 4: Holoien et al (2016b), 5: Nicholl et al (2019), 6: Leloudas et al (2019), 7: Holoien et al (2020), 8: van Velzen et al (2021b), 9: Gomez et al (2020), 10: Holoien et al (2019), 11: Cannizzaro et al (2021), 12: Nicholl et al (2020), 13: Gezari et al (2008), 14: Wyrzykowski et al (2017), 15: Gezari et al (2012), 16: Chornock et al (2014), 17: Arcavi et al (2014), 18: van Velzen et al (2011), 19: Hung et al (2017), 20: Blagorodnova et al (2017). 𝑎 From van Velzen et al (2021a); 𝑏 Exclude late-time data (see section 2.2); 𝑐 Shortened prior on 𝑡 exp < 30 d.; 𝑑 Although listed as TDE-H byvan Velzen et al (2021a), we classify here as TDE-H+He due to the detection of He II and likely N III byShort et al (2020). We have verified that the re-classification of this event does not change our statistical conclusions.…”

“…This accretion luminosity must also be reprocessed to generate the observed temperatures, but this would occur in a more compact atmosphere or accretion-driven wind (Metzger & Stone 2016). The higher densities in TDE-H+He events would also increase the efficiency of the Bowen fluorescence mechanism, as pointed out by van Velzen et al (2021a).…”

“…This work is based on publicly available data from the Open TDE Catalog (Guillochon et al 2017) and from van Velzen et al (2021a).…”

First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z &lt; 0.6

“…If the circumnuclear medium of a TDE is dusty, a significant fraction of the UV/optical radiation energy will be absorbed by dust and reprocessed to the IR (Lu, Kumar & Evans 2016). The resulting IR echoes bear important information on the dust properties at subpc scales in quiescent galaxies (van Velzen et al 2016(van Velzen et al , 2021a.…”