The role of newly born magnetars in gamma-ray burst X-ray afterglow emission: Energy injection and internal emission

TL;DR

This paper explores how newly born millisecond magnetars influence gamma-ray burst X-ray afterglows through energy injection and internal emission, suggesting magnetars can explain various observed afterglow phases and allowing parameter estimation.

Contribution

It introduces a modified energy injection model considering magnetar spin evolution and internal emission, linking observed X-ray afterglow phases to magnetar properties.

Findings

Some X-ray afterglows are internally produced by magnetars.

Magnetar parameters can be inferred from internal X-ray afterglows.

External shocks relate to different types of X-ray afterglows.

Abstract

Swift observations suggest that the central compact objects of some gamma-ray bursts (GRBs) could be newly born millisecond magnetars. Therefore, by considering the spin evolution of the magnetars against r-mode instability, we investigate the role of the magnetars in GRB X-ray afterglow emission. Besides modifying the conventional energy injection model, we pay particular attention to the internal X-ray afterglow emission, whose luminosity is assumed to track the magnetic dipole luminosity of the magentars with a certain fraction. Following a comparison between the model and some selected observational samples, we suggest that some so-called "canonical" X-ray afterglows including the shallow decay, normal decay, and steeper-than-normal decay phases could be internally produced by the magnetars (possibly through some internal dissipations of the magnetar winds), while the (energized) external shocks are associated with another type of X-ray afterglows. If this is true, from those internal X-ray afterglows, we can further determine the magnetic field strengths and the initial spin periods of the corresponding magnetars.