A1 Refereed original research article in a scientific journal
LSQ13fn: A type II-Plateau supernova with a possibly low metallicity progenitor that breaks the standardised candle relation
Authors: Polshaw J, Kotak R, Dessart L, Fraser M, Gal-Yam A, Inserra C, Sim SA, Smartt SJ, Sollerman J, Baltay C, Rabinowitz D, Benetti S, Botticella MT, Campbell H, Chen TW, Galbany L, McKinnon R, Nicholl M, Smith KW, Sullivan M, Takats K, Valenti S, Young DR, Young DR
Publisher: EDP SCIENCES S A
Publication year: 2016
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: ARTN A1
Volume: 588
Number of pages: 17
ISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/201527682
Abstract
We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a type II supernova with several hitherto-unseen properties. Although it initially showed strong symmetric spectral emission features attributable to He II, N III, and C III, reminiscent of some interacting SNe, it transitioned into an object that would fall more naturally under a type II-Plateau (IIP) classification. However, its spectral evolution revealed several unusual properties: metal lines appeared later than expected, were weak, and some species were conspicuous by their absence. Furthermore, the line velocities were found to be lower than expected given the plateau brightness, breaking the SN IIP standardised candle method for distance estimates. We found that, in combination with a short phase of early-time ejecta-circumstellar material interaction, metal-poor ejecta, and a large progenitor radius could reasonably account for the observed behaviour. Comparisons with synthetic model spectra of SNe IIP of a given progenitor mass would imply a progenitor star metallicity as low as 0.1 Z(circle dot). LSQ13fn highlights the diversity of SNe II and the many competing physical e ff ects that come into play towards the final stages of massive star evolution immediately preceding core-collapse.
We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a type II supernova with several hitherto-unseen properties. Although it initially showed strong symmetric spectral emission features attributable to He II, N III, and C III, reminiscent of some interacting SNe, it transitioned into an object that would fall more naturally under a type II-Plateau (IIP) classification. However, its spectral evolution revealed several unusual properties: metal lines appeared later than expected, were weak, and some species were conspicuous by their absence. Furthermore, the line velocities were found to be lower than expected given the plateau brightness, breaking the SN IIP standardised candle method for distance estimates. We found that, in combination with a short phase of early-time ejecta-circumstellar material interaction, metal-poor ejecta, and a large progenitor radius could reasonably account for the observed behaviour. Comparisons with synthetic model spectra of SNe IIP of a given progenitor mass would imply a progenitor star metallicity as low as 0.1 Z(circle dot). LSQ13fn highlights the diversity of SNe II and the many competing physical e ff ects that come into play towards the final stages of massive star evolution immediately preceding core-collapse.
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