Fig. 6: Spectral evolution expected in case of adiabatic cooling (solid lines) superimposed to the extended sample.
From: Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts
In a, the theoretical curves are computed considering adiabatic cooling and inefficient synchrotron cooling, taking also into account the effect of HLE. The value of λ specifies the evolution of the magnetic field. We adopt a SBPL as spectral shape with αs = −1/3 and βs = 2.0, an initial observed peak frequency of 100 keV and a thickness of the expanding shell that is constant in time. In b we show the spectral evolution expected in case of combined adiabatic cooling and mild synchrotron cooling. The adopted spectral shape is a SBPL plus an exponential cutoff. The initial peak frequency is 100 keV. The theoretical curves are computed taking also into account the effect of HLE. In both panels, the error bars represent 1σ uncertainties, calculated via spectral fitting in XSPEC, and the dot-dashed line is the evolution expected considering only HLE, assuming the same spectral shape and initial observed peak frequency. In the legend, we report the name of each GRB.
