RINGO3 polarimetry of very young ZTF supernovae

Abstract

The early phases of the observed evolution of the supernovae (SNe) are expected to be dominated by the shock breakout and ``flash" ionization of the surrounding circumstellar medium. This material arises from the last stages of the evolution of the progenitor, such that photometry and spectroscopy of SNe at early times can place vital constraints on the latest and fastest evolutionary phases leading up to stellar death. These signatures are erased by the expansion of the ejecta within ~5 days after explosion. Here we present the earliest constraints, to date, on the polarization of ten transients discovered by the Zwicky Transient Facility (ZTF), between June 2018 and August 2019. Rapid polarimetric followup was conducted using the Liverpool Telescope RINGO3 instrument, including 3 SNe observed within <1 day of detection by the ZTF. The limits on the polarization within the first 5 days of explosion, for all SN types, is generally <2%, implying early asymmetries are limited to axial ratios >0.65 (assuming an oblate spheroidal configuration). We also present polarimetric observations of the Type I Superluminous SN 2018bsz and Type II SN 2018hna, observed around and after maximum light.

13 pages, 7 figures

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• Polarimetry of Hydrogen-Poor Superluminous Supernovae
• The Core Normal Type Ia Supernova 2019np: An Overall Spherical Explosion with an Aspherical Surface Layer and an Aspherical 56Ni Core
• A flash of polarized optical light points to an aspherical "cow"
• Optical polarization and spectral properties of the H-poor superluminous supernovae SN 2021bnw and SN 2021fpl
• Inferring CSM Properties of Type II SNe Using a Magnitude-Limited ZTF Sample
• Post maximum light and late time optical imaging polarimetry of type I superluminous supernova 2020znr
• Pre-maximum spectroscopic diversity of hydrogen-poor superluminous supernovae
• SN 2018hna: Adding a Piece to the Puzzles of the Explosion of Blue Supergiants
• Can galactic magnetic fields diffuse into the voids?
• Spectropolarimetry of the Type Ia SN 2019ein rules out significant global asphericity of the ejecta
• Rare events of a peculiar thermonuclear supernova that precedes a core collapse supernova
• Magnetic field spreading from stellar and galactic dynamos into the exterior