Scary Barbie: An Extremely Energetic, Long-duration Tidal Disruption Event Candidate without a Detected Host Galaxy at z = 0.995

Creators: Subrayan, Bhagya M.; Milisavljevic, Dan; Chornock, Ryan; Margutti, Raffaella; Alexander, Kate D.; Ramakrishnan, Vandana; Duffell, Paul C.; Dickinson, Danielle A.; Lee, Kyoung-Soo; Giannios, Dimitrios; Lentner, Geoffery; Linvill, Mark; Garretson, Braden; Graham, Matthew J.; Stern, Daniel; Brethauer, Daniel; Duong, Tien; Jacobson-Galán, Wynn; LeBaron, Natalie; Matthews, David; Sears, Huei; Venkatraman, Padma

Abstract

We report multiwavelength observations and characterization of the ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka "Barbie") identified in the alert stream of the Zwicky Transient Facility (ZTF) using a Recommender Engine For Intelligent Transient Tracking filter on the ANTARES alert broker. From a spectroscopically measured redshift of 0.995, we estimate a peak-observed pseudo-bolometric luminosity of log(L_(ₘₐₓ)/[erg s⁻¹]) = 45.7 from slowly fading ztf-g and ztf-r light curves spanning over 1000 observer-frame days. The host galaxy is not detected in archival Pan-STARRS observations (g > 23.3 mag), implying a lower limit to the outburst amplitude of more than 5 mag relative to the quiescent host galaxy. Optical spectra exhibit strong emission lines with narrow cores from the H Balmer series and ultraviolet semi-forbidden lines of Si ɪɪɪ] λ1892, C ɪɪɪ] λ1909, and C ɪɪ] λ2325. Typical nebular lines in Active Galactic Nucleus (AGN) spectra from ions such as [O ɪɪ] and [O ɪɪɪ] are not detected. These spectral features, along with the smooth light curve that is unlike most AGN flaring activity and the luminosity that exceeds any observed or theorized supernova, lead us to conclude that AT 2021lwx is most likely an extreme tidal disruption event (TDE). Modeling of ZTF photometry with MOSFiT suggests that the TDE was between a ≈ 14M_⊙ star and a supermassive black hole of mass M_(BH) ∼ 10⁸M_⊙. Continued monitoring of the still-evolving light curve along with deep imaging of the field once AT 2021lwx has faded can test this hypothesis and potentially detect the host galaxy.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. We thank the referee for suggestions that have improved the content and presentation of this paper. D.M. acknowledges NSF support from grants PHY-1914448, PHY- 2209451, AST-2037297, and AST-2206532. The TReX group at Berkeley is partially supported by NSF grants AST-2221789 and AST-2224255. W.J.-G. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1842165. W.J.-G. acknowledges support from NASA grants through Hubble Space Telescope programs GO-16075, 16500 and 16922. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory, led by Brad Holden, was made possible through gifts from the Heising-Simons Foundation, William and Marina Kast, and the University of California Observatories. Research at Lick Observatory is partially supported by a generous gift from Google. We thank the staffs at Lick and Keck Observatories for their expert assistance in obtaining these observations. This research has made use of the CIRADA cutout service at URL cutouts.cirada.ca, operated by the Canadian Initiative for Radio Astronomy Data Analysis (CIRADA). CIRADA is funded by a grant from the Canada Foundation for Innovation 2017 Innovation Fund (Project 35999), as well as by the Provinces of Ontario, British Columbia, Alberta, Manitoba and Quebec, in collaboration with the National Research Council of Canada, the US National Radio Astronomy Observatory and Australia's Commonwealth Scientific and Industrial Research Organisation.

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