The Origin of Cross-Energy-Similar FRED Profiles in Gamma-Ray Bursts Pulses

TL;DR

This paper proposes a physical model for single FRED-profile gamma-ray bursts, explaining their self-similar morphology, spectral evolution, and multi-band features, and challenges traditional GRB duration interpretations.

Contribution

It introduces a sequential radiation triggering model driven by magnetic perturbations that accounts for key observed properties of FRED GRBs.

Findings

Explains the self-similar FRED profile and multi-band aligned subpulses.

Reconciles GRB duration with non-central engine activity.

Accounts for spectral evolution and subpulse duration increase.

Abstract

To understand the physical mechanisms underlying the prompt emission of gamma-ray bursts (GRB), single FRED (Fast-Rise-Exponential-Decay) profile GRBs serve as an ideal sample, as they origin from single epoch central engine activity. These GRBs have been found to exhibit a peculiar morphology-including the elegant cross-energy-similarity across energy bands and the recently discovered composite nature-challenging nearly all existing radiation mechanisms, sparking widespread curiosity about their origins. Here we propose a physical model which includes radiation locations sequentially triggered by propagating magnetic perturbations. It naturally explains all observed properties of these GRBs, including the self-similar FRED profile, multi-band aligned subpulses, hard-to-soft spectral evolution, local intensity tracking, and increasing subpulse durations. Furthermore, our results demonstrate that the duration of these GRBs is not reflecting the activity timescale of the central engine, reconciling recent challenges to the traditional merger-short/collapsar-long dichotomy of GRBs.