Dependence of the GRB Lag-Luminosity Relation on Redshift in the Source Frame

TL;DR

This study investigates whether the lag-luminosity relation in gamma-ray bursts depends on redshift by analyzing a sample of 43 Swift bursts, considering corrections, and examining parameter evolution with redshift.

Contribution

It introduces an analysis of the redshift dependence of the GRB lag-luminosity relation using a sizable Swift burst sample with corrections and binning by redshift.

Findings

Both the normalization and slope of the relation vary with redshift.

The relation shows systematic evolution, but data scatter and sample size limit conclusions.

Results are tentative due to large scatter and limited sample size.

Abstract

The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, tau_lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: log(L) = A + Blog(tau_lag0/<tau_lag0>) for each bin, where tau_lag0 is the time-lag in the burst's source frame, and <tau_lag0> is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with omega_M = 0.27, omega_lambda = 0.73, and a Hubble constant, H_0 = 70 km s-1 Mpc-1 is assumed.