SN 2018gjx reveals that some SNe Ibn are SNe IIb exploding in dense circumstellar material

S. J. Prentice*, K. Maguire, I. Boian, J. Groh, J. Anderson, C. Barbarino, K. A. Bostroem, J. Burke, P. Clark, Y. Dong, M. Fraser, L. Galbany, M. Gromadzki, C. P. Gutiérrez, D. A. Howell, D. Hiramatsu, C. Inserra, P. A. James, E. Kankare, H. KuncarayaktiP. A. Mazzali, C. McCully, T. E. Müller-Bravo, M. Nichol, C. Pellegrino, S. J. Smartt, J. Sollerman, L. Tartaglia, S. Valenti, D. R. Young

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

We present the data and analysis of SN 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. Phase I shows a hot blue spectrum with signatures of ionized circumstellar material (CSM), Phase II has the appearance of broad SN features, consistent with those seen in a Type IIb supernova at maximum light, and Phase III is that of a supernova interacting with helium-rich CSM, similar to a Type Ibn supernova. This event provides an apparently rare opportunity to view the inner workings of an interacting supernova. The observed properties can be explained by the explosion of a star in an aspherical CSM. The initial light is emitted from an extended CSM (~4000 R⊙), which ionizes the exterior unshocked material. Some days after, the SN photosphere envelops this region, leading to the appearance of a SN IIb. Over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the CSM that partially obscures the supernova nebular phase. Modelling of the initial spectrum reveals a surface composition consistent with compact H-deficient Wolf-Rayet and Luminous Blue Variable (LBV) stars. Such configurations may not be unusual, with SNe IIb being known to have signs of interaction so at least some SNe IIb and SNe Ibn may be the same phenomena viewed from different angles, or possibly with differing CSM configurations.

Original languageEnglish
Pages (from-to)1450-1467
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Volume499
Issue number1
Early online date25 Sep 2020
DOIs
Publication statusPublished - 01 Nov 2020

Bibliographical note

Funding Information:
SJP and KM are supported by H2020 ERC grant no. 758638. Research by KAB, SV, and YD is supported by NSF grant AST- 1813176. DAH, DH, JB, and CP are supported by NSF grants AST-1911225 and AST-1911151, and NASA grant 1518168. CM was supported by NSF AST-1313484. This paper made use of data from the LCO network. LG was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 839090, and by the Spanish grant PGC2018-095317-B-C21. CPG acknowledges support from EU/FP7-ERC grant no. [615929]. MG is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017- 72180113. MN is supported by a Royal Astronomical Society Research Fellowship. SJS acknowledges funding from STFCGrant Ref: ST/P000312/1. HK was funded by the Academy of Finland projects 324504 and 328898. LT acknowledges support from MIUR (PRIN 2017 grant 20179ZF5KS). 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. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.D-0143. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogues from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, and the Space Telescope Science Institute. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. Partly based on observations made with the Nordic Optical Telescope, operated at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. ALFOSC is provided by the Instituto de Astrofisica de Andalucia (IAA). We thank the anonymous referee for their time and comments, which improved this manuscript.

Funding Information:
SJP and KM are supported by H2020 ERC grant no. 758638. Research by KAB, SV, and YD is supported by NSF grant AST-1813176. DAH, DH, JB, and CP are supported by NSF grants AST-1911225 and AST-1911151, and NASA grant 1518168. CM was supported by NSF AST-1313484. This paper made use of data from the LCO network. LG was funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 839090, and by the Spanish grant PGC2018-095317-B-C21. CPG acknowledges support from EU/FP7-ERC grant no. [615929]. MG is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113. MN is supported by a Royal Astronomical Society Research Fellowship. SJS acknowledges funding from STFC Grant Ref: ST/P000312/1. HK was funded by the Academy of Finland projects 324504 and 328898. LT acknowledges support from MIUR (PRIN 2017 grant 20179ZF5KS). 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. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.D-0143. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogues from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, and the Space Telescope Science Institute. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. Partly based on observations made with the Nordic Optical Telescope, operated at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. ALFOSC is provided by the Instituto de Astrofisica de Andalucia (IAA). We thank the anonymous referee for their time and comments, which improved this manuscript.

Publisher Copyright:
© 2020 The Author(s).

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

  • Supernovae: individual: SN 2018gjx

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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