PROBING CURVATURE EFFECTS IN THE FERMI GRB 110920

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.