@article{4f354b902baf432aa199d51aad068cb6,
title = "A nearby super-luminous supernova with a long pre-maximum & {"}plateau{"} and strong C II features",
abstract = "Context. Super-luminous supernovae (SLSNe) are rare events defined as being significantly more luminous than normal terminal stellar explosions. The source of the additional power needed to achieve such luminosities is still unclear. Discoveries in the local Universe (i.e. z < 0.1) are scarce, but afford dense multi-wavelength observations. Additional low-redshift objects are therefore extremely valuable. Aims. We present early-time observations of the type I SLSN ASASSN-18km/SN 2018bsz. These data are used to characterise the event and compare to literature SLSNe and spectral models. Host galaxy properties are also analysed. Methods. Optical and near-IR photometry and spectroscopy were analysed. Early-time ATLAS photometry was used to constrain the rising light curve. We identified a number of spectral features in optical-wavelength spectra and track their time evolution. Finally, we used archival host galaxy photometry together with H{\^a}€ II region spectra to constrain the host environment. Results. ASASSN-18km/SN 2018bsz is found to be a type I SLSN in a galaxy at a redshift of 0.0267 (111 Mpc), making it the lowest-redshift event discovered to date. Strong C II lines are identified in the spectra. Spectral models produced by exploding a Wolf-Rayet progenitor and injecting a magnetar power source are shown to be qualitatively similar to ASASSN-18km/SN 2018bsz, contrary to most SLSNe-I that display weak or non-existent C II lines. ASASSN-18km/SN 2018bsz displays a long, slowly rising, red {"}plateau{"} of >26 days, before a steeper, faster rise to maximum. The host has an absolute magnitude of -19.8 mag (r), a mass of M* = 1.5-0.33 +0.08 × 109 M{\^a}{\v S}{\texttrademark}, and a star formation rate of = 0.50-0.19 +2.22 M{\^a}{\v S}{\texttrademark} yr-1. A nearby H{\^a}€ II region has an oxygen abundance (O3N2) of 8.31 ± 0.01 dex.",
keywords = "Supernovae: General, Supernovae: Individual: Asassn-18km, Supernovae: Individual: Sn 2018bsz",
author = "Anderson, {J. P.} and Pessi, {P. J.} and L. Dessart and C. Inserra and D. Hiramatsu and K. Taggart and Smartt, {S. J.} and G. Leloudas and Chen, {T. W.} and A. M{\"o}ller and R. Roy and S. Schulze and D. Perley and J. Selsing and Prentice, {S. J.} and A. Gal-Yam and Angus, {C. R.} and I. Arcavi and C. Ashall and M. Bulla and C. Bray and J. Burke and E. Callis and R. Cartier and Chang, {S. W.} and K. Chambers and P. Clark and L. Denneau and M. Dennefeld and H. Flewelling and M. Fraser and L. Galbany and M. Gromadzki and Guti{\'e}rrez, {C. P.} and A. Heinze and G. Hosseinzadeh and Howell, {D. A.} and Hsiao, {E. Y.} and E. Kankare and Z. Kostrzewa-Rutkowska and E. Magnier and K. Maguire and P. Mazzali and O. McBrien and C. McCully and N. Morrell and Lowe, {T. B.} and Onken, {C. A.} and F. Onori and Phillips, {M. M.} and A. Rest and R. Ridden-Harper and Ruiter, {A. J.} and Sand, {D. J.} and Smith, {K. W.} and M. Smith and B. Stalder and Stritzinger, {M. D.} and M. Sullivan and Tonry, {J. L.} and Tucker, {B. E.} and S. Valenti and R. Wainscoat and Waters, {C. Z.} and C. Wolf and D. Young",
note = "Funding Information: Acknowledgements. We thank the staff at Paranal for their efficiency in obtaining our observations. James Leftley is thanked for help with the SED fitting of the SN photometry. This work is based (in part) on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile as part of ePESSTO, (the extended Public ESO Spectroscopic Survey for Transient Objects Survey) programme 199.D-0143. Based on (in part) observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme(s) 2101.D-5023(A). Based on observations obtained at the Gemini Observatory under programme GS-2018AQ-107 (PI: Sand). Gemini is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnolog{\'i}a e Inno-vaci{\'o}n Productiva (Argentina), and Minist{\'e}rio da Ci{\^e}ncia, Tecnologia e Ino-va{\c c}{\~a}o (Brazil). Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). SJS acknowledges funding from STFC Grant Ref: ST/P000312/1. GL is supported by a research grant (19054) from VILLUM FONDEN. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. TWC acknowledgments the funding provided by the Alexander von Humboldt Foundation. Support for this work was provided by NASA grant NN12AR55G. Research by DJS is supported by NSF grants AST-1821987 and 1821967. This work makes use of observations from the Las Cumbres Observatory network. DAH, CM, and GH are supported by NSF grant AST 1313484. A.G.-Y. is supported by the EU via ERC grant No. 725161, the Quantum Universe I-Core program, the ISF, the BSF Transformative program and by a Kimmel award. Support for IA was provided by NASA through the Einstein Fellowship Program, grant PF6-170148. LG was supported in part by the US National Science Foundation under Grant AST-1311862. MG is supported by the Polish National Science Centre grant OPUS 2015/17/B/ST9/03167. MF is supported by a Royal Society – Science Foundation Ireland University Research Fellowship. KM is supported by STFC through an Ernest Rutherford fellowship. MB acknowledges support from the Swedish Research Council (Vetenskapsr{\aa}det) and the Swedish National Space Board. AJR is funded by the Australian Research Council through grant number FT170100243. MDS is funded by a research grant (13261) from the Villum foundation. Parts of this project were conducted by the Australian Research Council Centre of Excellence for All-sky Astro-physics (CAASTRO), through project number CE110001020. EYH and CA acknowledge the support provided by the National Science Foundation under grant No. AST-1613472. ZKR acknowledges support from European Research Council Consolidator Grant 647208. This research was supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This research has made use of data, software and/or web tools obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Astrophysics Science Division at NASA/GSFC and of the Smith-sonian Astrophysical Observatory{\textquoteright}s High Energy Astrophysics Division. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. We thank the Swift ToO team for executing of our observations. Pan-STARRS is supported by the University of Hawaii and the NASA{\textquoteright}s Planetary Defense Office under Grant no. NNX14AM74G. GALEX (Galaxy Evolution Explorer) is a NASA Small Explorer, launched in April 2003. We gratefully acknowledge NASA{\textquoteright}s support for construction, operation, and science analysis of the GALEX mission, developed in cooperation with the Centre National d{\textquoteright}Etudes Spatiales of France and the Korean Ministry of Science and Technology. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. The national facility capability for SkyMapper has been funded through ARC LIEF grant LE130100104 from the Australian Research Council, awarded to the University of Sydney, the Australian National University, Swinburne University of Technology, the University of Queensland, the University of Western Australia, the University of Melbourne, Curtin University of Technology, Monash University and the Australian Astronomical Observatory. SkyMapper is owned and operated by The Australian National University{\textquoteright}s Research School of Astronomy and Astrophysics. The survey data were processed and provided by the SkyMapper Team at ANU. The SkyMapper node of the All-Sky Virtual Observatory (ASVO) is hosted at the National Computational Infrastructure (NCI). Development and support the SkyMapper node of the ASVO has been funded in part by Astronomy Australia Limited (AAL) and the Australian Government through the Commonwealth{\textquoteright}s Education Investment Fund (EIF) and National Collaborative Research Infrastructure Strategy (NCRIS), particularly the National eResearch Collaboration Tools and Resources (NeCTAR) and the Australian National Data Service Projects (ANDS). MMP acknowledges support from the National Science Foundation under grant No. AST-1613426. Funding Information: MMP acknowledges support from the National Science Foundation under grant No. AST-1613426 Publisher Copyright: {\textcopyright} ESO 2018.",
year = "2018",
month = dec,
day = "1",
doi = "10.1051/0004-6361/201833725",
language = "English (US)",
volume = "620",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}