Steep Slopes and Preferred Breaks in Gamma‐Ray Burst Spectra: The Role of Photospheres and Comptonization

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Abstract
The role of a photospheric component and of pair breakdown is examined in the internal shock model of gamma-ray bursts. We discuss some of the mechanisms by which they would produce anomalously steep low-energy slopes, X-ray excesses and preferred energy breaks. Subrelativistic Comptonization should dominate in high comoving luminosity bursts with high baryon load, while synchrotron radiation dominates the power-law component in bursts which have lower comoving luminosity or have moderate to low baryon loads. A photosphere leading to steep low-energy spectral slopes should be prominent in the lowest baryon load cases.