The nearby luminous transient AT2018cow: a magnetar formed in a sub-relativistically expanding non-jetted explosion

Abstract

The fast-rising blue optical transient AT2018cow indicated unusual early phase characteristics unlike relatively better studied explosive transients. Its afterglow may be produced by either a relativistically beamed (jetted) or intrinsically luminous (non-jetted) ejecta and carries observational signatures of the progenitor and environment. High resolution monitoring can distinguish between these scenarios and clarify the progenitor nature. We present very long baseline interferometry (VLBI) observations of AT2018cow at 5 GHz involving 21 radio telescopes from the European VLBI Network with five sessions spanning ~ 1 year. With an astrometric precision up to 25 micro-arcseconds per epoch, the rapidly fading compact milli arcsecond scale source is found to be non-jetted with a proper motion of <= 0.15 mas/yr (0.14 c). This and a dense (number density ~ 10^4 - 10^5/cm^3) magnetized environment (magnetic field strength >= 0.84 G) are characteristic of a newly formed magnetar driven central engine, originating in the successful explosion of a low-mass star.

12 pages, 4 figures, 4 tables. Accepted for publication in ApJ Letters

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• Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs
• A common envelope jets supernova (CEJSN) impostor scenario for fast blue optical transients
• A Wind-Driven Model: Application to Peculiar Transients AT2018cow and iPTF14hls
• Status and progress of China SKA Regional Centre prototype
• An environmental analysis of the fast transient AT2018cow and implications for its progenitor and late-time brightness
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• Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV bright Underlying Source 2--4 Yr Post-discovery
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• MUSSES2020J: The Earliest Discovery of a Fast Blue Ultraluminous Transient at Redshift 1.063
• A compact core-jet structure in the changing-look Seyfert NGC 2617
• New candidates for magnetar counterparts from a deep search with the Hubble Space Telescope
• Late-time Hubble Space Telescope Observations of AT 2018cow. I. Further Constraints on the Fading Prompt Emission and Thermal Properties 50--60 Days Post-discovery
• Real-time Discovery of AT2020xnd: A Fast, Luminous Ultraviolet Transient with Minimal Radioactive Ejecta
• Deep VLBI Observations Challenge Previous Evidence of a Binary Supermassive Black Hole Residing in the Seyfert Galaxy NGC 7674
• A Population Study on the Radio Emission of Fast Blue Optical Transients
• Terminating a common envelope jets supernova impostor event with a super-Eddington blue supergiant
• Light-curve Modelling for The Initial Rising Phase of Rapidly-evolving Transients Powered by Continuous Outflow
• A study on late time UV-emission in core collapse supernovae and the implications for the peculiar transient AT2018cow