SN 2020ank: a bright and fast-evolving H-deficient superluminous supernova

Abstract

We investigate the observational properties of a hydrogen-deficient superluminous supernova (SLSN) SN 2020ank (at z = 0.2485), with the help of early phase observations carried out between –21 and +52 d since g-band maximum. Photometrically, SN 2020ank is one of the brightest SLSN (⁠Mg,peak∼ –21.84 ± 0.10 mag), having fast pre-peak rising and post-peak decaying rates. The bolometric light curve of SN 2020ank exhibits a higher peak luminosity (Lmax) of ∼ (3.9 ± 0.7) × 1044 erg s−1 and appears to be symmetric around the peak with Lrisemax/e ≈Lfallmax/e ≈ 15 d. The semi-analytical light-curve modelling using the minim code suggests a spin-down millisecond magnetar with Pi∼ 2.2 ± 0.5 ms and B∼ (2.9 ± 0.1) ×1014 G as a possible powering source for SN 2020ank. The possible magnetar origin and excess ultraviolet flux at early epochs indicate a central-engine based powering source for SN 2020ank. Near-peak spectra of SN 2020ank are enriched with the W-shaped O ii features but with the weaker signatures of C ii and Fe iii. Using the estimated rise time of ∼ 27.9 d and the photospheric velocity of ∼ 12 050 km s−1, we constrain the ejecta mass to ∼ 7.2 M⊙ and the kinetic energy of ∼6.3 × 1051 erg. The near-peak spectrum of SN 2020ank exhibits a close spectral resemblance with that of fast-evolving SN 2010gx. The absorption features of SN 2020ank are blueshifted compared to Gaia16apd, suggesting a higher expansion velocity. The spectral similarity with SN 2010gx and comparatively faster spectral evolution than PTF12dam (a slow-evolving SLSN) indicate the fast-evolving behaviour of SN 2020ank.