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

The role of a photospheric component and of pair breakdown is examined in theinternal shock model of gamma-ray bursts. We discuss some of the mechanisms bywhich they would produce anomalously steep low energy slopes, X-ray excessesand preferred energy breaks. Sub-relativistic comptonization should dominate inhigh comoving luminosity bursts with high baryon load, while synchrotronradiation dominates the power law component in bursts which have lower comovingluminosity or have moderate to low baryon loads. A photosphere leading to steeplow energy spectral slopes should be prominent in the lowest baryon loadComment: ApJ'00, in press; minor revs. 10/5/99; (uses aaspp4.sty), 15 pages, 3 figure