On a GRB afterglow model consistent with hypernovae observations

TL;DR

This paper models the afterglow of GRB 130427A within a binary-driven hypernova framework, explaining multi-wavelength observations through interactions between a newly formed neutron star and hypernova ejecta.

Contribution

It introduces a novel afterglow model based on a binary hypernova scenario, incorporating the interaction of a neutron star and hypernova ejecta, differing from traditional jet models.

Findings

Reproduces afterglow from optical to X-ray over days to years.

Determines mildly relativistic expansion velocity independently.

Shows energy injection from hypernova kinetic energy and neutron star rotation.

Abstract

We describe the afterglows of the long gamma-ray-burst (GRB) 130427A within the context of a binary-driven hypernova (BdHN). The afterglows originate from the interaction between a newly born neutron star ($\nu$NS), created by an Ic supernova (SN), and a mildly relativistic ejecta of a hypernova (HN). Such a HN in turn results from the impact of the GRB on the original SN Ic. The mildly relativistic expansion velocity of the afterglow ($\Gamma \sim 3$) is determined, using our model independent approach, from the thermal emission between $196$~s and $461$~s. The power-law in the optical and X-ray bands of the afterglow is shown to arise from the synchrotron emission of relativistic electrons in the expanding magnetized HN ejecta. Two components contribute to the injected energy: the kinetic energy of the mildly relativistic expanding HN and the rotational energy of the fast rotating highly magnetized $\nu$NS. We reproduce the afterglow in all wavelengths from the optical ($10^{14}$~Hz) to the X-ray band ($10^{19}$~Hz) over times from $604$~s to $5.18\times 10^6$~s relative to the Fermi-GBM trigger. Initially, the emission is dominated by the loss of kinetic energy of the HN component. After $10^5$~s the emission is dominated by the loss of rotational energy of the $\nu$NS, for which we adopt an initial rotation period of $2$~ms and a dipole plus quadrupole magnetic field of $\lesssim \! 7\times 10^{12}$~G or $\sim \! 10^{14}$~G. This scenario with a progenitor composed of a CO$_{\rm core}$ and a NS companion differs from the traditional ultra-relativistic-jetted treatments of the afterglows originating from a single black hole.