SN 2020zbf: A fast-rising hydrogen-poor superluminous supernova with strong carbon lines

¹ The Oskar Klein Centre, Department of Astronomy, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
e-mail: anamaria.gkini@astro.su.se
² The Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 106 91 Stockholm, Sweden
³ Institut d’Astrophysique de Paris, CNRS-Sorbonne Université, 98 bis boulevard Arago, 75014 Paris, France
⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK
⁵ The Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, 20014 Turku, Finland
⁷ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
⁸ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
⁹ Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
¹⁰ Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, 32001 Jhongli, Taiwan
¹¹ Las Cumbres Observatory, 6740 Cortona Dr. Suite 102, Goleta, CA 93117, USA
¹² Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
¹³ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
¹⁴ Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2-4, Edifici Nexus, Desp. 201, 08034 Barcelona, Spain
¹⁵ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
¹⁶ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138-1516, USA
¹⁷ The NSF AI Institute for Artificial Intelligence and Fundamental Interactions, MIT, Cambridge MA 02139, USA
¹⁸ Cardiff Hub for Astrophysics Research and Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁹ Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
²⁰ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

Received: 5 October 2023
Accepted: 23 January 2024

Abstract

SN 2020zbf is a hydrogen-poor superluminous supernova (SLSN) at z = 0.1947 that shows conspicuous C II features at early times, in contrast to the majority of H-poor SLSNe. Its peak magnitude is M_g = −21.2 mag and its rise time (≲26.4 days from first light) places SN 2020zbf among the fastest rising type I SLSNe. We used spectra taken from ultraviolet (UV) to near-infrared wavelengths to identify spectral features. We paid particular attention to the C II lines as they present distinctive characteristics when compared to other events. We also analyzed UV and optical photometric data and modeled the light curves considering three different powering mechanisms: radioactive decay of ⁵⁶Ni, magnetar spin-down, and circumstellar medium (CSM) interaction. The spectra of SN 2020zbf match the model spectra of a C-rich low-mass magnetar-powered supernova model well. This is consistent with our light curve modeling, which supports a magnetar-powered event with an ejecta mass M_ej = 1.5 M_⊙. However, we cannot discard the CSM-interaction model as it may also reproduce the observed features. The interaction with H-poor, carbon-oxygen CSM near peak light could explain the presence of C II emission lines. A short plateau in the light curve around 35–45 days after peak, in combination with the presence of an emission line at 6580 Å, can also be interpreted as being due to a late interaction with an extended H-rich CSM. Both the magnetar and CSM-interaction models of SN 2020zbf indicate that the progenitor mass at the time of explosion is between 2 and 5 M_⊙. Modeling the spectral energy distribution of the host galaxy reveals a host mass of 10^8.7 M_⊙, a star formation rate of 0.24_−0.12^+0.41 M_⊙ yr⁻¹, and a metallicity of ∼0.4 Z_⊙.