How Temporal Symmetry Defines Morphology in BATSE Gamma-Ray Burst Pulse Light Curves

TL;DR

This study reveals that gamma-ray burst pulse light curves are predominantly temporally symmetric, allowing accurate modeling and prediction of their morphology based on symmetry and structural alignment, with implications for understanding GRB populations.

Contribution

The paper demonstrates that GRB pulse light curves can be modeled using temporal symmetry, providing a new predictive framework for pulse morphology based on symmetry and structural parameters.

Findings

86% of bright BATSE GRB pulses fit the symmetry model

Morphological types correlate with specific asymmetries and durations

Short GRB pulses share similar structures with long GRB pulses but on shorter timescales

Abstract

We present compelling evidence that most gamma-ray burst (GRB) pulse light curves can be characterized by a smooth single-peaked component coupled with a more complex emission structure that is temporally-symmetric around the time of the pulse peak. The model successfully fits 86% of BATSE GRB pulses bright enough for structure properties to be measured. Surprisingly, a GRB pulse's light curve morphology can be accurately predicted by the pulse asymmetry and the stretching/compression needed to align the structural components preceding the temporal mirror with the time-reversed components following it. Such a prediction is only possible because GRB pulses exhibit temporal symmetry. Time-asymmetric pulses include FREDs, rollercoaster pulses, and asymmetric u-pulses, while time-symmetric pulses include u-pulses and crowns. Each morphological type is characterized by specific asymmetries, stretching parameters, durations, and alignments between the smooth and structured components, and a delineation in the asymmetry/stretching distribution suggests that symmetric pulses and asymmetric pulses may belong to separate populations. Furthermore, pulses belonging to the short GRB class exhibit similar morphologies to the long GRB class, but appear to simply occur on shorter timescales.