# Simulations of light curves and spectra for superluminous Type Ic supernovae powered by magnetars

## TL;DR

This study uses detailed radiative transfer simulations to explore how magnetar-powered superluminous Type Ic supernovae evolve in light curves and spectra, highlighting the effects of magnetar properties and ejecta clumping.

## Contribution

It provides the first comprehensive non-LTE time-dependent radiative transfer models of magnetar-powered SLSNe Ic, including effects of clumping and spectral diversity.

## Key findings

- Magnetar power boosts ejecta temperature and ionization.
- Clumping influences spectral line formation and diversity.
- Most observed SLSNe Ic require ejecta clumping from early to nebular phases.

## Abstract

Numerous superluminous supernovae (SLSNe) of Type Ic have been discovered and monitored in the last decade. The favored mechanism at their origin is a sustained power injection from a magnetar. This study presents non-local thermodynamic equilibrium time-dependent radiative transfer simulations of various single carbon-rich Wolf-Rayet star explosions influenced by magnetars of diverse properties and covering from a few days to one or two years after explosion. Nonthermal processes are treated; the magnetar-power deposition profile is prescribed; dynamical effects are ignored. In this context, the main influence of the magnetar power is to boost the internal energy of the ejecta on week-long time scales, enhancing the ejecta temperature and ionization, shifting the spectral energy distribution to the near-UV (even for the adopted solar metallicity), creating blue optical colors. Varying the ejecta and magnetar properties introduces various stretches and shifts to the light curve (rise time, peak or nebular luminosity, light curve width). At maximum, all models show the presence of OII and CII lines in the optical, and more rarely OIII and CIII lines. Non-thermal effects are found to be negligible during the high-brightness phase. After maximum, higher energy explosions are hotter and more ionized, and produce spectra that are optically bluer. Clumping is a source of spectral diversity after maximum. Clumping is essential to trigger ejecta recombination and yield the presence of OI, CaII, and FeII lines from a few weeks after maximum until nebular times. The UV and optical spectrum of Gaia16apd at maximum or the nebular spectrum of LSQ14an at +410d are compatible with some models that assume no clumping. However, most observed SLSNe Ic seem to require clumping from early post-maximum to nebular times (e.g., SN2007bi at +46 and +367d; Gaia16apd at +43d).