Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope

Giorgos Leloudas; Justyn R. Maund; Avishay Gal-yam; Tapio Pursimo; Eric Hsiao; Daniele Malesani; Ferdinando Patat; Antonio De Ugarte Postigo; Jesper Sollerman; Maximilian D. Stritzinger; J. Craig Wheeler

doi:10.3847/2041-8213/aa6157

Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope

Giorgos Leloudas, Justyn R. Maund, Avishay Gal-yam, Tapio Pursimo, Eric Hsiao, Daniele Malesani, Ferdinando Patat, Antonio De Ugarte Postigo, Jesper Sollerman, Maximilian D. Stritzinger, J. Craig Wheeler

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23 Citations (Scopus)

Abstract

We present imaging polarimetry of the superluminous supernova SN 2015bn, obtained over nine epochs between -20 and +46 days with the Nordic Optical Telescope. This was a nearby, slowly evolving Type I superluminous supernova that has been studied extensively and for which two epochs of spectropolarimetry are also available. Based on field stars, we determine the interstellar polarization in the Galaxy to be negligible. The polarization of SN 2015bn shows a statistically significant increase during the last epochs, confirming previous findings. Our well-sampled imaging polarimetry series allows us to determine that this increase (from ∼0.54% to ≳1.10%) coincides in time with rapid changes that took place in the optical spectrum. We conclude that the supernova underwent a "phase transition" at around +20 days, when the photospheric emission shifted from an outer layer, dominated by natal C and O, to a more aspherical inner core, dominated by freshly nucleosynthesized material. This two-layered model might account for the characteristic appearance and properties of Type I superluminous supernovae.

Original language	English
Journal	The Astrophysical Journal Letters
Volume	837
Issue number	1
Pages (from-to)	L14
ISSN	2041-8205
DOIs	https://doi.org/10.3847/2041-8213/aa6157
Publication status	Published - 1 Mar 2017

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title = "Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope",

abstract = "We present imaging polarimetry of the superluminous supernova SN 2015bn, obtained over nine epochs between -20 and +46 days with the Nordic Optical Telescope. This was a nearby, slowly evolving Type I superluminous supernova that has been studied extensively and for which two epochs of spectropolarimetry are also available. Based on field stars, we determine the interstellar polarization in the Galaxy to be negligible. The polarization of SN 2015bn shows a statistically significant increase during the last epochs, confirming previous findings. Our well-sampled imaging polarimetry series allows us to determine that this increase (from ∼0.54% to ≳1.10%) coincides in time with rapid changes that took place in the optical spectrum. We conclude that the supernova underwent a {"}phase transition{"} at around +20 days, when the photospheric emission shifted from an outer layer, dominated by natal C and O, to a more aspherical inner core, dominated by freshly nucleosynthesized material. This two-layered model might account for the characteristic appearance and properties of Type I superluminous supernovae.",

author = "Giorgos Leloudas and Maund, {Justyn R.} and Avishay Gal-yam and Tapio Pursimo and Eric Hsiao and Daniele Malesani and Ferdinando Patat and {De Ugarte Postigo}, Antonio and Jesper Sollerman and Stritzinger, {Maximilian D.} and Wheeler, {J. Craig}",

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T1 - Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope

AU - Leloudas, Giorgos

AU - Maund, Justyn R.

AU - Gal-yam, Avishay

AU - Pursimo, Tapio

AU - Hsiao, Eric

AU - Malesani, Daniele

AU - Patat, Ferdinando

AU - De Ugarte Postigo, Antonio

AU - Sollerman, Jesper

AU - Stritzinger, Maximilian D.

AU - Wheeler, J. Craig

PY - 2017/3/1

Y1 - 2017/3/1

N2 - We present imaging polarimetry of the superluminous supernova SN 2015bn, obtained over nine epochs between -20 and +46 days with the Nordic Optical Telescope. This was a nearby, slowly evolving Type I superluminous supernova that has been studied extensively and for which two epochs of spectropolarimetry are also available. Based on field stars, we determine the interstellar polarization in the Galaxy to be negligible. The polarization of SN 2015bn shows a statistically significant increase during the last epochs, confirming previous findings. Our well-sampled imaging polarimetry series allows us to determine that this increase (from ∼0.54% to ≳1.10%) coincides in time with rapid changes that took place in the optical spectrum. We conclude that the supernova underwent a "phase transition" at around +20 days, when the photospheric emission shifted from an outer layer, dominated by natal C and O, to a more aspherical inner core, dominated by freshly nucleosynthesized material. This two-layered model might account for the characteristic appearance and properties of Type I superluminous supernovae.

AB - We present imaging polarimetry of the superluminous supernova SN 2015bn, obtained over nine epochs between -20 and +46 days with the Nordic Optical Telescope. This was a nearby, slowly evolving Type I superluminous supernova that has been studied extensively and for which two epochs of spectropolarimetry are also available. Based on field stars, we determine the interstellar polarization in the Galaxy to be negligible. The polarization of SN 2015bn shows a statistically significant increase during the last epochs, confirming previous findings. Our well-sampled imaging polarimetry series allows us to determine that this increase (from ∼0.54% to ≳1.10%) coincides in time with rapid changes that took place in the optical spectrum. We conclude that the supernova underwent a "phase transition" at around +20 days, when the photospheric emission shifted from an outer layer, dominated by natal C and O, to a more aspherical inner core, dominated by freshly nucleosynthesized material. This two-layered model might account for the characteristic appearance and properties of Type I superluminous supernovae.

U2 - 10.3847/2041-8213/aa6157

DO - 10.3847/2041-8213/aa6157

M3 - Journal article

SN - 2041-8205

VL - 837

SP - L14

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

IS - 1

ER -

Time-resolved Polarimetry of the Superluminous SN 2015bn with the Nordic Optical Telescope

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