Probing Curvature Effects in the Fermi GRB 110920

TL;DR

This paper investigates how curvature effects influence gamma-ray burst observations by comparing a simple kinematic model to data from GRB 110920, focusing on spectral and temporal features during the decay phase.

Contribution

It introduces a two-shell collision model for a uniform jet to explain curvature effects and tests its predictions against Fermi GRB data, providing insights into GRB emission mechanisms.

Findings

Model reproduces the peak-flux--peak-frequency relation during decay.

Spectral lags are consistent with curvature effects.

Pulse width behavior with energy supports the model.

Abstract

Curvature effects in Gamma-ray bursts (GRBs) have long been a source of considerable interest. In a collimated relativistic GRB jet, photons that are off-axis relative to the observer arrive at later times than on-axis photons and are also expected to be spectrally softer. In this work, we invoke a relatively simple kinematic two-shell collision model for a uniform jet profile and compare its predictions to GRB prompt-emission data for observations that have been attributed to curvature effects such as the peak-flux--peak-frequency relation, i.e., the relation between the $\nu$F$_\nu$ flux and the spectral peak, E$_{pk}$ in the decay phase of a GRB pulse, and spectral lags. In addition, we explore the behavior of pulse widths with energy. We present the case of the single-pulse Fermi GRB 110920, as a test for the predictions of the model against observations.