Solving the 56Ni puzzle of magnetar-powered broad-lined type Ic supernovae

TL;DR

This paper introduces a dynamic magnetar-powered supernova model that explains the observed 56Ni production in broad-lined type Ic supernovae, resolving previous conflicts between theory and observations.

Contribution

The authors develop a model accounting for ejecta acceleration and thermal energy deposition, showing magnetars can produce observed 56Ni levels in SNe Ic-BL.

Findings

A tiny fraction of magnetar energy suffices to produce 0.06 solar mass of 56Ni.

The model explains the energetics and nucleosynthesis of SNe Ic-BL.

Magnetars can power SNe Ic-BL effectively.

Abstract

Broad-lined type Ic supernovae (SNe Ic-BL) are of great importance because their association with long-duration gamma-ray bursts (LGRBs) holds the key to deciphering the central engine of LGRBs, which refrains from being unveiled despite decades of investigation. Among the two popularly hypothesized types of central engine, i.e., black holes and strongly magnetized neutron stars (magnetars), there is mounting evidence that the central engine of GRB-associated SNe (GRB-SNe) is rapidly rotating magnetars. Theoretical analysis also suggests that magnetars could be the central engine of SNe Ic-BL. What puzzled the researchers is the fact that light curve modeling indicates that as much as 0.2-0.5 solar mass of 56Ni was synthesized during the explosion of the SNe Ic-BL, which is unfortunately in direct conflict with current state-of-the-art understanding of magnetar-powered 56Ni synthesis. Here we propose a dynamic model of magnetar-powered SNe to take into account the acceleration of the ejecta by the magnetar, as well as the thermalization of the injected energy. Assuming that the SN kinetic energy comes exclusively from the magnetar acceleration, we find that although a major fraction of the rotational energy of the magnetar is to accelerate the SNe ejecta, a tiny fraction of this energy deposited as thermal energy of the ejecta is enough to reduce the needed 56Ni to 0.06 solar mass for both SN 1997ef and SN 2007ru. We therefore suggest that magnetars could power SNe Ic-BL both in aspects of energetics and of 56Ni synthesis.