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A precursor plateau and pre-maximum [O ii] emission in the superluminous SN2019szu: a pulsational pair-instability candidate
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).ORCID iD: 0000-0001-8005-4030
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Number of Authors: 322023 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 527, no 4, p. 11970-11995Article in journal (Refereed) Published
Abstract [en]

We present a detailed study on SN2019szu, a Type I superluminous supernova at z = 0.213 that displayed unique photometric and spectroscopic properties. Pan-STARRS and ZTF forced photometry show a pre-explosion plateau lasting ∼40 d. Unlike other SLSNe that show decreasing photospheric temperatures with time, the optical colours show an apparent temperature increase from ∼15 000 to ∼20 000 K over the first 70 d, likely caused by an additional pseudo-continuum in the spectrum. Remarkably, the spectrum displays a forbidden emission line (likely attributed to λλ7320,7330) visible 16 d before maximum light, inconsistent with an apparently compact photosphere. This identification is further strengthened by the appearances of [O III] λλ4959, 5007, and [O III] λ4363 seen in the spectrum. Comparing with nebular spectral models, we find that the oxygen line fluxes and ratios can be reproduced with ∼0.25 M of oxygen-rich material with a density of ∼10−15 g cm−3⁠. The low density suggests a circumstellar origin, but the early onset of the emission lines requires that this material was ejected within the final months before the terminal explosion, consistent with the timing of the precursor plateau. Interaction with denser material closer to the explosion likely produced the pseudo-continuum bluewards of ∼5500 Å. We suggest that this event is one of the best candidates to date for a pulsational pair-instability ejection, with early pulses providing the low density material needed for the formation of the forbidden emission line, and collisions between the final shells of ejected material producing the pre-explosion plateau.

Place, publisher, year, edition, pages
2023. Vol. 527, no 4, p. 11970-11995
Keywords [en]
stars: massive, supernovae: general, supernovae: individual: SN2019szu, transients: supernovae
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-226499DOI: 10.1093/mnras/stad3776ISI: 001157351800001Scopus ID: 2-s2.0-85182401745OAI: oai:DiVA.org:su-226499DiVA, id: diva2:1838738
Available from: 2024-02-19 Created: 2024-02-19 Last updated: 2024-03-12Bibliographically approved

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Jerkstrand, AndersSchulze, Steve

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Nicholl, MattJerkstrand, AndersSrivastav, ShubhamGao, HuaGutiérrez, Claudia P.Schulze, Steve
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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Monthly notices of the Royal Astronomical Society
Astronomy, Astrophysics and Cosmology

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