Radio and X-Ray Observations of the Luminous Fast Blue Optical Transient at 2020xnd

Joe S. Bright*, Raffaella Margutti, David Matthews, Daniel Brethauer, Deanne Coppejans, Mark H. Wieringa, Brian D. Metzger, Lindsay Demarchi, Tanmoy Laskar, Charles Romero, Kate D. Alexander, Assaf Horesh, Giulia Migliori, Ryan Chornock, E. Berger, Michael Bietenholz, Mark J. Devlin, Simon R. Dicker, W. V. Jacobson-Galán, Brian S. MasonDan Milisavljevic, Sara E. Motta, Tony Mroczkowski, Enrico Ramirez-Ruiz, Lauren Rhodes, Craig L. Sarazin, Itai Sfaradi, Jonathan Sievers

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


We present deep X-ray and radio observations of the fast blue optical transient (FBOT) AT 2020xnd/ZTF 20acigmel at z = 0.2433 from 13 days to 269 days after explosion. AT 2020xnd belongs to the category of optically luminous FBOTs with similarities to the archetypal event AT 2018cow. AT 2020xnd shows luminous radio emission reaching L ν ≈ 8 × 1029 erg s-1 Hz-1 at 20 GHz and 75 days post-explosion, accompanied by luminous and rapidly fading soft X-ray emission peaking at L X ≈ 6 × 1042 erg s-1. Interpreting the radio emission in the context of synchrotron radiation from the explosion's shock interaction with the environment, we find that AT 2020xnd launched a high-velocity outflow (v ∼0.1c-0.2c) propagating into a dense circumstellar medium (effective Ṁ≈10-3M yr-1 for an assumed wind velocity of v w = 1000 km s-1). Similar to AT 2018cow, the detected X-ray emission is in excess compared to the extrapolated synchrotron spectrum and constitutes a different emission component, possibly powered by accretion onto a newly formed black hole or neutron star. These properties make AT 2020xnd a high-redshift analog to AT 2018cow, and establish AT 2020xnd as the fourth member of the class of optically luminous FBOTs with luminous multiwavelength counterparts.

Original languageAmerican English
Article number112
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Feb 2022

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© 2022. The Author(s). Published by the American Astronomical Society.


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