Central Engine Memory of Gamma-Ray Bursts and Soft Gamma-Ray Repeaters

TL;DR

This paper discovers that some gamma-ray bursts and soft gamma-ray repeaters exhibit similar light curve patterns, indicating their central engines have a form of memory, challenging existing black hole models and suggesting magnetars as a common engine.

Contribution

It introduces a novel application of Dynamic Time Warping to identify memory-like features in GRB and SGR light curves, proposing magnetars as the central engine.

Findings

Light curve patterns are similar within individual GRBs and between GRBs and SGRs.

Memory-like emission episodes are identified in SGRs, indicating a shared mechanism.

Challenges the black hole engine model, supporting magnetar-based explanations.

Abstract

Gamma-ray Bursts (GRBs) are bursts of $\gamma$-rays generated from relativistic jets launched from catastrophic events such as massive star core collapse or binary compact star coalescence. Previous studies suggested that GRB emission is erratic, with no noticeable memory in the central engine. Here we report a discovery that similar light curve patterns exist within individual bursts for at least some GRBs. Applying the Dynamic Time Warping (DTW) method, we show that similarity of light curve patterns between pulses of a single burst or between the light curves of a GRB and its X-ray flare can be identified. This suggests that the central engine of at least some GRBs carries "memory" of its activities. We also show that the same technique can identify memory-like emission episodes in the flaring emission in Soft Gamma-Ray Repeaters (SGRs), which are believed to be Galactic, highly magnetized neutron stars named magnetars. Such a phenomenon challenges the standard black hole central engine models for GRBs, and suggest a common physical mechanism behind GRBs and SGRs, which points towards a magnetar central engine of GRBs.