Spectral Lags Explained as Scattering from Accelerated Scatterers

TL;DR

This paper presents a quantitative model explaining gamma-ray burst spectral lags as resulting from scattering by accelerated baryons, successfully matching observed energy dependence and luminosity relations.

Contribution

It introduces a novel scattering-based theory for GRB spectral lags, linking photon energy, pulse shape, and luminosity in a unified framework.

Findings

Pulse width scales as E_ph^{-0.4} near cutoff

Spectral lag inversely proportional to luminosity

Model matches observed pulse asymmetry and energy dependence

Abstract

A quantitative theory of spectral lags for $\gamma$-ray bursts (GRBs) is given. The underlying hypothesis is that GRB subpulses are photons that are scattered into our line of sight by local concentrations of baryons that are accelerated by radiation pressure. For primary spectra that are power laws with exponential cutoffs, the width of the pulse and its fast rise, slow decay asymmetry is found to increase with decreasing photon energy, and the width near the exponential cutoff scales approximately as $E_{ph}^{-\eta}$, with $\eta\sim 0.4$, as observed. The spectral lag time is naturally inversely proportional to luminosity, all else being equal, also as observed.