SN 2020qlb: A hydrogen-poor superluminous supernova with well-characterized light curve undulations

¹ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
e-mail: stuartlwest@icloud.com
² The Oskar Klein Centre, Department of Physics, KTH Royal Institute of Technology, AlbaNova, 106 91 Stockholm, Sweden
³ The Oskar Klein Centre, Department of Physics, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
⁴ Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100, Israel
⁵ Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park, 146 Brownlow Hill, Liverpool L35RF, UK
⁶ The Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Physics Department and Tsinghua Center for Astrophysics (THCA), Tsingua University, Beijing 100084, PR China
⁸ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁹ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
¹⁰ Department of Astronomy, University of California, Berkeley, CA 94720, USA
¹¹ Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA
¹² IPAC, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA

Received: 23 May 2022
Accepted: 28 November 2022

Abstract

Context. SN 2020qlb (ZTF20abobpcb) is a hydrogen-poor superluminous supernova (SLSN-I) that is among the most luminous (maximum M_g = −22.25 mag) and that has one of the longest rise times (77 days from explosion to maximum). We estimate the total radiated energy to be > 2.1 × 10⁵¹ erg. SN 2020qlb has a well-sampled light curve that exhibits clear near and post peak undulations, a phenomenon seen in other SLSNe, whose physical origin is still unknown.

Aims. We discuss the potential power source of this immense explosion as well as the mechanisms behind its observed light curve undulations.

Methods. We analyze photospheric spectra and compare them to other SLSNe-I. We constructed the bolometric light curve using photometry from a large data set of observations from the Zwicky Transient Facility (ZTF), Liverpool Telescope (LT), and Neil Gehrels Swift Observatory and compare it with radioactive, circumstellar interaction and magnetar models. Model residuals and light curve polynomial fit residuals are analyzed to estimate the undulation timescale and amplitude. We also determine host galaxy properties based on imaging and spectroscopy data, including a detection of the [O III]λ4363, auroral line, allowing for a direct metallicity measurement.

Results. We rule out the Arnett ⁵⁶Ni decay model for SN 2020qlb’s light curve due to unphysical parameter results. Our most favored power source is the magnetic dipole spin-down energy deposition of a magnetar. Two to three near peak oscillations, intriguingly similar to those of SN 2015bn, were found in the magnetar model residuals with a timescale of 32 ± 6 days and an amplitude of 6% of peak luminosity. We rule out centrally located undulation sources due to timescale considerations; and we favor the result of ejecta interactions with circumstellar material (CSM) density fluctuations as the source of the undulations.