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A flash of polarized optical light points to an aspherical ‘cow’

Maund, JR, Höflich, PA, Steele, IA, Yang, Y, Wiersema, K, Kobayashi, S, Jordana-Mitjans, N, Mundell, C, Gomboc, A, Guidorzi, C and Smith, RJ (2023) A flash of polarized optical light points to an aspherical ‘cow’. Monthly Notices of the Royal Astronomical Society, 521 (3). pp. 3323-3332. ISSN 0035-8711

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The astronomical transient AT2018cow is the closest example of the new class of luminous, fast blue optical transients (FBOTs). Liverpool Telescope RINGO3 observations of AT 2018cow are reported here, which constitute the earliest polarimetric observations of an FBOT. At 5.7 days post-explosion, the optical emission of AT2018cow exhibited a chromatic polarization spike that reached ∼7% at red wavelengths. This is the highest intrinsic polarization recorded for a non-relativistic explosive transient, and is observed in multiple bands and at multiple epochs over the first night of observations, before rapidly declining. The apparent wavelength dependence of the polarization may arise through depolarization or dilution of the polarized flux, due to conditions in AT 2018cow at early times. A second ‘bump’ in the polarization is observed at blue wavelengths at ∼12 days. Such a high polarization requires an extremely aspherical geometry that is only apparent for a brief period (<1 day), such as shock breakout through an optically thick disk. For a disk-like configuration, the ratio of the thickness to radial extent must be ∼10%⁠.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 21 Mar 2023 10:15
Last Modified: 05 Apr 2023 08:45
DOI or ID number: 10.1093/mnras/stad539
URI: https://researchonline.ljmu.ac.uk/id/eprint/19147
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