A MAD Model for Gamma-Ray Burst Variability

TL;DR

This paper introduces a magnetically arrested disk (MAD) model to explain the rapid variability observed in the prompt phase of long gamma-ray bursts, linking magnetic flux dynamics to observed timescales.

Contribution

It presents a novel MAD-based framework that models GRB variability through magnetic flux interactions and provides analytic estimates matching observed timescales.

Findings

Reproduces the characteristic one-second variability timescale.

Explains the correlation between quiescent times and subsequent pulse durations.

Aligns model energetics and timescales with gamma-ray burst observations.

Abstract

We present a model for the temporal variability of long gamma-ray bursts during the prompt phase (the highly variable first 100 seconds or so), in the context of a magnetically arrested disk (MAD) around a black hole. In this state, sufficient magnetic flux is held on to the black hole such that it stalls the accretion near the inner region of the disk. The system transitions in and out of the MAD state, which we relate to the variable luminosity of the GRB during the prompt phase, with a characteristic timescale defined by the free fall time in the region over which the accretion is arrested. We present simple analytic estimates of the relevant energetics and timescales, and compare them to gamma-ray burst observations. In particular, we show how this model can reproduce the characteristic one second time scale that emerges from various analyses of the prompt emission light curve. We also discuss how our model can accommodate the potentially physically important correlation between a burst quiescent time and the duration of its subsequent pulse (Ramirez-Ruiz & Merloni 2001).