Delayed Energy Injection Model For Gamma-Ray Burst Afterglows

TL;DR

This paper introduces a delayed energy injection model for gamma-ray burst afterglows, explaining re-brightening features by considering fall-back accretion delays, and links these phenomena to progenitor star properties.

Contribution

The model accounts for delayed energy injection causing afterglow re-brightening, extending previous models by incorporating fall-back accretion delays and explaining observed optical and infrared features.

Findings

Explains re-brightening in GRB afterglows with delayed energy injection.

Links fall-back accretion timing to progenitor star properties.

Fits observed light curves of specific GRBs.

Abstract

The shallow decay phase and flares in the afterglows of gamma-ray bursts (GRBs) is widely believed to be associated with the later activation of central engine. Some models of energy injection involve with a continuous energy flow since the GRB trigger time, such as the magnetic dipole radiation from a magnetar. However, in the scenario involving with a black hole accretion system, the energy flow from the fall-back accretion may be delayed for a fall-back time $\sim t_{\rm fb}$. Thus we propose a delayed energy injection model, the delayed energy would cause a notable rise to the Lorentz factor of the external shock, which will "generate" a bump in the multiple band afterglows. If the delayed time is very short, our model degenerates to the previous models. Our model can well explain the significant re-brightening in the optical and infrared light curves of GRB 081029 and GRB 100621A. A considerable fall-back mass is needed to provide the later energy, this indicates GRBs accompanied with fall-back material may be associated with a low energy supernova so that fraction of the envelope can be survived during eruption. The fall-back time can give meaningful information of the properties of GRB progenitor stars.