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arXiv · 2110.05514

Radio and X-ray observations of the luminous Fast Blue Optical Transient AT2020xnd

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. Mason·Dan Milisavljevic·Sara E. Motta·Tony Mroczkowski·Enrico Ramirez-Ruiz·Lauren Rhodes·Craig L. Sarazin·Itai Sfaradi·Jonathan Sievers
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Abstract

We present deep X-ray and radio observations of the Fast Blue Optical Transient (FBOT) AT2020xnd/ZTF20acigmel at $z=0.2433$ from $13$d to $269$d after explosion. AT2020xnd belongs to the category of optically luminous FBOTs with similarities to the archetypal event AT2018cow. AT2020xnd shows luminous radio emission reaching $L_{\nu}\approx8\times10^{29}$ergs$^{-1}$Hz$^{-1}$ at 20GHz and $75$d post explosion, accompanied by luminous and rapidly fading soft X-ray emission peaking at $L_{X}\approx6\times10^{42}$ergs$^{-1}$. Interpreting the radio emission in the context of synchrotron radiation from the explosion's shock interaction with the environment we find that AT2020xnd launched a high-velocity outflow ($v\sim$0.1-0.2$c$) propagating into a dense circumstellar medium (effective $\dot M\approx10^{-3}M_{\rm{sol}}$yr$^{-1}$ for an assumed wind velocity of $v_w=1000$kms$^{-1}$). Similar to AT2018cow, 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 AT2020xnd a high-redshift analog to AT2018cow, and establish AT2020xnd as the fourth member of the class of optically-luminous FBOTs with luminous multi-wavelength counterparts.

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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. Mason, Dan Milisavljevic, Sara E. Motta, Tony Mroczkowski, Enrico Ramirez-Ruiz, Lauren Rhodes, Craig L. Sarazin, Itai Sfaradi, Jonathan Sievers. 2021-10-11. Radio and X-ray observations of the luminous Fast Blue Optical Transient AT2020xnd. https://doi.org/10.3847/1538-4357%2Fac4506

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