On Some Statistical Properties of GRBs with Measured Redshifts Having Peaks in Optical Light Curves

Abstract

We studied the subset of optical light curves of gamma-ray bursts with measured redshifts and well-sampled R band data that have clearly detected peaks. Among 43 such events, 11 are promptoptical peaks (P), coincident with gamma-ray activity, 22 are purely afterglows (A), and 10 more carrythe signatures of an underlying activity (A(U)). We studied pair correlations of their gamma-ray andoptical parameters, e.g. total energetics, peak optical luminosities, and durations. The main outcomeof our study is the detection of source frame correlations between both optical peak luminosity and total energy and the redshift for classes A and A(U), and the absence of such a correlation for class Pevents. This result seems to provide evidence of the cosmological evolution of a medium around the burst defining class A and A(U) energetics, and the absence of cosmological evolution of the internal properties of GRB engines. We also discuss some other prominent correlations.