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

Justyn R. Maund; Peter A.  Hoflich; Iain A. Steele; Yi Yang; Klaas Wiersema; Shiho Kobayashi; Nuria Jordana-Mitjans; Carole Mundell; Andreja Gomboc; Cristiano Guidorzi; Robert J. Smith

doi:10.1093/mnras/stad539

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

Justyn R. Maund, Peter A. Hoflich, Iain A. Steele, Yi Yang, Klaas Wiersema, Shiho Kobayashi, Nuria Jordana-Mitjans, Carole Mundell, Andreja Gomboc, Cristiano Guidorzi, Robert J. Smith

Department of Physics

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Abstract

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 d), 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%.

Original language	English
Pages (from-to)	3323-3332
Number of pages	10
Journal	Monthly Notices of the Royal Astronomical Society
Volume	521
Issue number	3
DOIs	https://doi.org/10.1093/mnras/stad539
Publication status	Published - 1 May 2023

Bibliographical note

UKRI funded (via STFC)

Acknowledgement:
JRM acknowledges support by the Science and Technologies Facilities Council (STFC) grant ST/V000853/1. PAH acknowledges support by the National Science Foundation (NSF) grant AST-1715133. The research of YY is supported through a Bengier-Winslow-Robertson Fellowship. KW acknowledges funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme awarded to Prof A. Levan (grant agreement no 725246) and from a UK Research and Innovation Future Leaders Fellowship awarded to Dr. B. Simmons (MR/T044136/1). AG acknowledges the financial support from the Slovenian Research Agency (grants P1-0031, I0-0033, J1-8136, J1-2460). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council (STFC). This research made use of Photutils, an Astropy package for detection, and photometry of astronomical sources (Bradley et al. 2020).

DATA AVAILABILITY:
The Liverpool Telescope RINGO3 data presented here are available through the publicly accessible Liverpool Telescope archive: https://telescope.livjm.ac.uk/cgi-bin/lt_search

Keywords

stars
supernovae:individual:AT 2018cow
technique:polarimetric

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.1093/mnras/stad539

2303.00787
This is a pre-copyedited, author-produced version of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Justyn R Maund and others, A flash of polarized optical light points to an aspherical ‘cow’, Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 3, May 2023, Pages 3323–3332, https://doi.org/10.1093/mnras/stad539 is available online at: https://academic.oup.com/mnras/article/521/3/3323/7049972?login=true https://doi.org/10.1093/mnras/stad539
Accepted author manuscript, 1.51 MBLicence: Unspecified

Cite this

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title = "A flash of polarized optical light points to an aspherical {\textquoteleft}cow{\textquoteright}",

abstract = "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 d), 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%.",

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author = "Maund, {Justyn R.} and Hoflich, {Peter A.} and Steele, {Iain A.} and Yi Yang and Klaas Wiersema and Shiho Kobayashi and Nuria Jordana-Mitjans and Carole Mundell and Andreja Gomboc and Cristiano Guidorzi and Smith, {Robert J.}",

note = "UKRI funded (via STFC) Acknowledgement: JRM acknowledges support by the Science and Technologies Facilities Council (STFC) grant ST/V000853/1. PAH acknowledges support by the National Science Foundation (NSF) grant AST-1715133. The research of YY is supported through a Bengier-Winslow-Robertson Fellowship. KW acknowledges funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme awarded to Prof A. Levan (grant agreement no 725246) and from a UK Research and Innovation Future Leaders Fellowship awarded to Dr. B. Simmons (MR/T044136/1). AG acknowledges the financial support from the Slovenian Research Agency (grants P1-0031, I0-0033, J1-8136, J1-2460). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council (STFC). This research made use of Photutils, an Astropy package for detection, and photometry of astronomical sources (Bradley et al. 2020). DATA AVAILABILITY: The Liverpool Telescope RINGO3 data presented here are available through the publicly accessible Liverpool Telescope archive: https://telescope.livjm.ac.uk/cgi-bin/lt_search",

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AU - Hoflich, Peter A.

AU - Steele, Iain A.

AU - Yang, Yi

AU - Wiersema, Klaas

AU - Kobayashi, Shiho

AU - Jordana-Mitjans, Nuria

AU - Mundell, Carole

AU - Gomboc, Andreja

AU - Guidorzi, Cristiano

AU - Smith, Robert J.

N1 - UKRI funded (via STFC) Acknowledgement: JRM acknowledges support by the Science and Technologies Facilities Council (STFC) grant ST/V000853/1. PAH acknowledges support by the National Science Foundation (NSF) grant AST-1715133. The research of YY is supported through a Bengier-Winslow-Robertson Fellowship. KW acknowledges funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme awarded to Prof A. Levan (grant agreement no 725246) and from a UK Research and Innovation Future Leaders Fellowship awarded to Dr. B. Simmons (MR/T044136/1). AG acknowledges the financial support from the Slovenian Research Agency (grants P1-0031, I0-0033, J1-8136, J1-2460). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council (STFC). This research made use of Photutils, an Astropy package for detection, and photometry of astronomical sources (Bradley et al. 2020). DATA AVAILABILITY: The Liverpool Telescope RINGO3 data presented here are available through the publicly accessible Liverpool Telescope archive: https://telescope.livjm.ac.uk/cgi-bin/lt_search

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N2 - 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 d), 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%.

AB - 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 d), 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%.

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DO - 10.1093/mnras/stad539

M3 - Article

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JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

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

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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