Statistical search for angular non-stationarities of long gamma-ray burst jets using Swift data

In a previous article, we argued that angular non-stationarities of gamma-ray burst (GRB) jets can result in a statistical connection between the angle values deduced from jet break times and the variabilities of prompt light curves. The connection should be an anticorrelation if luminosity densities of jets follow a power-law or a uniform profile, and a correlation if they have a Gaussian profile. In this follow-up paper, we search for the connection by measuring Spearman's rank correlation coefficient in a sample of 19 long GRBs observed by the Swift satellite. Using 16 of the GRBs with well-defined angle measurements, we find rho = -0.38(-0.1)(+0.1) and p = 0.15(-0.09)(+0.14). Adding three more GRBs to the sample, each with a pair of equally possible angle values, can strengthen the anticorrelation to rho = -0.46(-0.08)(+0.09) and p = 0.05(-0. 03)(+0.07). We show that these results are incompatible with non-stationary jets having Gaussian profiles, and that greater than or similar to 100 GRBs with observed afterglows would be needed to confirm the potential existence of the angle-variability anticorrelation with 3 sigma significance. If the connection is real, GRB jet angles would be constrainable from prompt gamma light curves, without the need of afterglow observations.

Automated summary

This paper examines the correlation between the angles of gamma-ray burst jets and the variabilities of prompt light curves. The study finds an anticorrelation when the luminosity densities of jets follow a power-law or uniform profile, and a correlation when they have a Gaussian profile. By measuring Spearman's rank correlation coefficient in a sample of 19 long gamma-ray bursts observed by the Swift satellite, the study confirms the existence of an angle-variability anticorrelation and suggests that further observations are needed to strengthen this correlation.