Gamma‐Ray Burst Spectral Correlations: Photospheric and Injection Effects

We present a physical framework that can account for most of the observedspectral properties of the prompt gamma-ray burst emission. This includes thevariety of spectral shapes, shape evolutions, and spectral correlations betweenflux and spectral peak, within bursts described by Borgonovo & Ryde, and amongbursts described by Amati/Ghirlanda. In our proposed model the spectral peak isgiven by the photospheric emission from a relativistic outflow for which thehorizon length is much smaller than the radial width. The observed duration ofthe thermal flash will be given by the radial light-crossing time. This thengives that the typical emission site is at ~10e11 cm from the center, with aLorentz factor of ~300. This emission is accompanied by non-thermal emissionfrom dissipation locations outside the photosphere. The relative strength ofthese two components depend on injection effects at the central engine leadingto varying relative location of the saturation and photospheric radii. Thetotal emission can then reproduce the observed variety. The spectralcorrelations are found by assuming that the amount of energy dissipated dependsnon-linearly on the averaged particle density. Beside the spectral correlationsthis also gives a description of how the relative strength of the thermalcomponent varies with temperature within a burst.Comment: ApJ accepted, acknowledgement adde