Spectral evolution of long gamma-ray bursts observed with Konus-Wind

Abstract

We present a preliminary analysis of spectral evolution of 35 long bright gamma-ray bursts (GRBs) detected by Konus-Wind instrument. From the temporal and spectral analyses of the sample, we investigate the evolution of parameters of the smoothly joined broken power-law spectral model (the Band “GRB” function), in particular, we analyse hardness-intensity correlation within a burst. We show that the bulk of bursts exhibit Ep ∝ F γ relation with the slope γ ∼ 0.3−0.5, where Ep is the vFv spectrum peak energy and F is the energy flux; while a number of events have the smooth initial phase with strong spectral evolution with γ ≳ 1. Finally, we discuss derived the Band function parameters and their evolution pattern in the framework of GRB emission models.