ALMA Polarimetry of AT2018cow

Abstract

We present the first radio polarimetric observations of a fast-rising blue optical transient, AT2018cow. Two epochs of polarimetry with additional coincident photometry were performed with the Atacama Large Millimeter/submillimeter Array (ALMA). The overall photometric results based on simultaneous observations in the 100 and 230 GHz bands are consistent with the non-thermal radiation model reported by Ho et al. (2019) and indicate that the spectral peaks ($\sim 110$ GHz at the first epoch and $\sim 67$ GHz at the second epoch) represent the synchrotron self-absorption frequency. The non-detection of linear polarization with $<$0.15% in the 230 GHz band at the phase when the effect of synchrotron self-absorption was quite small in the band may be explained by internal Faraday depolarization with high circumburst density and strong magnetic field. This result supports the stellar explosion scenario rather than the tidal disruption model. The maximum energy of accelerating particles at the shocks of AT2018cow-like objects is also discussed.

arXiv comment7 pages, 3 figures, 1 table, accepted for publication in ApJL

References in corpus (16)

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• X-ray Swift observations of SN 2018cow
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• SN 1993J VLBI (III): The Evolution of the Radio Shell
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• Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow
• The Peculiar Transient AT2018cow: A Possible Origin of A Type Ibn/IIn Supernova
• The nearby luminous transient AT2018cow: a magnetar formed in a sub-relativistically expanding non-jetted explosion
• 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
• Fast Blue Optical Transients due to Circumstellar Interaction and the Mysterious Supernova SN 2018gep
• An environmental analysis of the fast transient AT2018cow and implications for its progenitor and late-time brightness
• Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV bright Underlying Source 2--4 Yr Post-discovery
• A possible 250-second X-ray quasi-periodicity in the fast blue optical transient AT2018cow
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• Connection of supernovae 2002ap, 2003gd, 2013ej, and 2019krl in M74 with atomic gas accretion and spiral structure
• 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
• The Atacama Cosmology Telescope: Flux Upper Limits from a Targeted Search for Extragalactic Transients
• ALMA Host galaxy observation of the off-axis Gamma-Ray Burst XRF020903
• The X-ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-Driven Massive Star Explosions