Super-luminous supernovae: 56Ni power versus magnetar radiation

TL;DR

This paper compares the power sources of super-luminous supernovae, finding that magnetar radiation better explains their spectral features than nickel decay from pair-instability supernova models.

Contribution

It demonstrates that magnetar energy injection can reproduce the observed spectra of super-luminous supernovae more accurately than pair-instability supernova models.

Findings

PISN models produce red spectra inconsistent with observations.

Magnetar energy injection results in blue, broad-lined spectra matching super-luminous SNe.

A magnetar-influenced model reproduces diverse spectral morphologies.

Abstract

Much uncertainty surrounds the origin of super-luminous supernovae (SNe). Motivated by the discovery of the Type Ic SN2007bi, we study its proposed association with a pair-instability SN (PISN). We compute stellar-evolution models for primordial ~200Msun stars, simulating the implosion/explosion due to the pair-production instability, and use them as inputs for detailed non-LTE time-dependent radiative-transfer simulations that include non-local energy deposition and non-thermal processes. We retrieve the basic morphology of PISN light curves from red-supergiant, blue-supergiant, and Wolf-Rayet (WR) star progenitors. Although we confirm that a progenitor 100Msun helium core (PISN model He100) fits well the SN2007bi light curve, the low ratios of its kinetic energy and 56Ni mass to the ejecta mass, similar to standard core-collapse SNe, conspire to produce cool photospheres, red spectra subject to strong line blanketing, and narrow line profiles, all conflicting with SN2007bi observations. He-core models of increasing 56Ni-to-ejecta mass ratio have bluer spectra, but still too red to match SN2007bi, even for model He125 -- the effect of 56Ni heating is offset by the associated increase in blanketing. In contrast, the delayed injection of energy by a magnetar represents a more attractive alternative to reproduce the blue, weakly-blanketed, and broad-lined spectra of super-luminous SNe. The extra heat source is free of blanketing and is not explicitly tied to the ejecta. Experimenting with a ~9Msun WR-star progenitor, initially exploded to yield a ~1.6B SN Ib/c ejecta but later influenced by tunable magnetar-like radiation, we produce a diversity of blue spectral morphologies reminiscent of SN2007bi, the peculiar Type Ib SN2005bf, and super-luminous SN2005ap-like events.