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Self-intersection of the Fallback Stream in Tidal Disruption Events

Lu, Wenbin and Bonnerot, Clément (2020) Self-intersection of the Fallback Stream in Tidal Disruption Events. Monthly Notices of the Royal Astronomical Society, 492 (1). pp. 686-707. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20191223-154435847

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Abstract

We propose a semi-analytical model for the self-intersection of the fallback stream in tidal disruption events (TDEs). When the initial periapsis is less than about 15 gravitational radii, a large fraction of the shocked gas is unbound in the form of a collision-induced outflow (CIO). This is because large apsidal precession causes the stream to self-intersect near the local escape speed at radius much below the apocenter. The rest of the fallback gas is left in more tightly bound orbits and quickly joins the accretion flow. We propose that the CIO is responsible for reprocessing the hard emission from the accretion flow into the optical band. This picture naturally explains the large photospheric radius (or low blackbody temperature) and typical widths of the H and/or He emission lines seen in optical TDEs. We predict the CIO-reprocessed spectrum in the infrared to be L_ν ∝ ν^(~0.5), shallower than a blackbody. The partial sky coverage of the CIO also provides a unification of the diverse X-ray behaviors of optical TDEs. According to this picture, optical surveys filter out a large fraction of TDEs with low-mass blackholes due to lack of a reprocessing layer, and the volumetric rate of optical TDEs is nearly flat wrt. the blackhole mass for M ≾ 10⁷M⊙. This filtering causes the optical TDE rate to be lower than the total rate by a factor of ~10 or more. When the CIO is decelerated by the ambient medium, radio emission at the level of that in ASASSN-14li may be produced, but the timescales and peak luminosities can be highly diverse. Finally, our method paves the way for global simulations of the disk formation process by injecting gas at the intersection point according to the prescribed velocity and density profiles.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/mnras/stz3405DOIArticle
https://arxiv.org/abs/1904.12018arXivDiscussion Paper
ORCID:
AuthorORCID
Lu, Wenbin0000-0002-1568-7461
Bonnerot, Clément0000-0001-9970-2843
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2019 November 27. Received 2019 November 2; in original form 2019 April 22. Published: 04 December 2019. We are grateful for the discussions with with Eliot Quataert and Tony Piro on the radiative transfer in a reprocessing wind, with Brian Metzger and Dan Kasen on the absorption opacity, and with Sterl Phinney on the effects of stellar interior structure. We also thank Phil Hopkins, Bing Zhang, Shri Kulkarni, Brad Cenko, Sjoert van Velzen, and Jim Fuller for useful conversations. We are indebted to Brian Metzger and Pawan Kumar for reading an earlier version of the manuscript and providing valuable comments. We acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. This research benefited from interactions at the ZTF Theory Network Meeting, funded by the Gordon and Betty Moore Foundation through Grant GBMF5076 and by the National Science Foundation under Grant No. NSF PHY-1748958. WL was supported by the David and Ellen Lee Fellowship at Caltech.
Group:TAPIR
Funders:
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
NSFPHY-1748958
David and Ellen Lee Postdoctoral ScholarshipUNSPECIFIED
Subject Keywords:methods: analytical – galaxies: nuclei
Issue or Number:1
Record Number:CaltechAUTHORS:20191223-154435847
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191223-154435847
Official Citation:Wenbin Lu, Clément Bonnerot, Self-intersection of the fallback stream in tidal disruption events, Monthly Notices of the Royal Astronomical Society, Volume 492, Issue 1, February 2020, Pages 686–707, https://doi.org/10.1093/mnras/stz3405
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100424
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:24 Dec 2019 00:00
Last Modified:27 Feb 2020 17:39

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