SN 2019hcc: a Type II supernova displaying early O II lines
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Oxford University Press
Line: formationLine: identificationStars: magnetars
Eleonora Parrag... [et al.]. SN 2019hcc: a Type II supernova displaying early O II lines, Monthly Notices of the Royal Astronomical Society, Volume 506, Issue 4, October 2021, Pages 4819–4840, [https://doi.org/10.1093/mnras/stab2074]
SponsorshipEuropean Organisation for Astronomical Research in the Southern Hemisphere, Chile, ePESSTO/ePESSTO+ extended Public ESO Spectroscopic Survey for Transient Objects Survey). ePESSTO+ observations were obtained under ESO program) 1103.D-0328; Google Incorporated; European Space Agency's (ESA) Summer of Code in Space program; Alexander von Humboldt Foundation; EU under Marie Sklodowska-Curie H2020-MSCA-IF-2018-842471; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CHILE/2017-72180113; Polish Narodowe Centrum Nauki (NCN) MAESTRO grant 2014/14/A/ST9/00121; Royal Astronomical Society Research Fellowship; SKA South Africa 839090; European Commission PGC2018-095317-B-C21; VILLUM FONDEN 19054; National Science Foundation (NSF) AST-1911225 AST-1911151; National Aeronautics & Space Administration (NASA) 80NSSC19K1639 NN12AR55G 80NSSC18K0284 80NSSC18K1575; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC); European Union's Horizon 2020 research and innovation programme 730890; Kepler/K2 grant J1944/80NSSC19K0112 HST GO-15889; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC) ST/T000198/1 ST/S006109/1; Gaia Multilateral Agreement; GROND; German Research Foundation (DFG) HA 1850/28-1; European Southern Observatory (ESO) programme 0103.A-9099; National Aeronautics & Space Administration (NASA); ESO Telescopes at the La Silla or Paranal Observatories under ESO programme 179.A-2010
We present optical spectroscopy together with ultraviolet, optical, and near-infrared photometry of SN 2019hcc, which resides in a host galaxy at redshift 0.044, displaying a sub-solar metallicity. The supernova spectrum near peak epoch shows a ‘w’ shape at around 4000 Å which is usually associated with OII lines and is typical of Type I superluminous supernovae. SN 2019hcc post-peak spectra show a well-developed Hα P-Cygni profile from 19 d past maximum and its light curve, in terms of its absolute peak luminosity and evolution, resembles that of a fast-declining Hydrogen-rich supernova (SN IIL). The object does not show any unambiguous sign of interaction as there is no evidence of narrow lines in the spectra or undulations in the light curve. Our TARDIS spectral modelling of the first spectrum shows that carbon, nitrogen, and oxygen (CNO) at 19 000 K reproduce the ‘w’ shape and suggests that a combination of non-thermally excited CNO and metal lines at 8000K could reproduce the feature seen at 4000 Å. The Bolometric light-curve modelling reveals that SN 2019hcc could be fit with a magnetar model, showing a relatively strong magnetic field (B > 3 × 1014 G), which matches the peak luminosity and rise time without powering up the light curve to superluminous luminosities. The high-energy photons produced by the magnetar would then be responsible for the detected OII lines. As a consequence, SN 2019hcc shows that a ‘w’ shape profile at around 4000 Å, usually attributed to OII, is not only shown in superluminous supernovae and hence it should not be treated as the sole evidence of the belonging to such a supernova type.