Rebrightenings of gamma-ray burst afterglows from an increasing magnetic inclination angle of a nascent magnetar

TL;DR

This paper explores how an increasing magnetic inclination angle of a nascent magnetar influences energy injection into GRB afterglows, leading to observable rebrightening features in the light curves.

Contribution

It introduces a novel model where an increasing inclination angle causes rebrightenings in GRB afterglows, explaining observed features not accounted for by previous fixed or decreasing angle scenarios.

Findings

Rebrightening phases are linked to increasing inclination angles.

The model explains rebrightenings in GRB 170822A and GRB 230414B.

Short-lived, slight rebrightenings can result from this mechanism.

Abstract

A nascent magnetar, accompanying a gamma-ray burst (GRB) explosion, releases enormous rotational energy via magnetic dipole radiation. The energy loss rate of the magnetar is determined by the strength of the magnetic field at the pole. We investigated the effect of the magnetic inclination angle on the energy loss rate. The released energy is injected into the GRB jet and shapes the light curves of GRB afterglow. Different evolutionary approaches lead to different curves shapes.A shallow decay phase in GRB X-ray afterglow may result from energy injection from a magnetar with a fixed inclination angle. A two-plateau phase may result from a decreasing inclination angle scenario. In this study, we considered an increasing inclination angle scenario. The energy loss rate of the magnetar increases as the magnetic inclination angle grows. Our analysis reveals that as the lost rotational energy injected into the GRB jet increases, rebrightening phases occur in the GRB afterglows. The rebrightening features are slight and short-lived. The observed afterglow rebrightening of GRB 170822A and GRB 230414B can be well explained within our framework. Some GRB X-ray afterglows that exhibit slight and early rebrightenings may result from an increasing magnetic inclination angle of a nascent magnetar.