Simulations of Gamma‐Ray Bursts from External Shocks: Time Variability and Spectral Correlations

We compute burst spectra and time structures arising from synchrotron andinverse Compton scattering by non-thermal electrons accelerated in shocks whichform during the interaction between a thin ultra-relativistic fireball and astationary external medium. We investigate the effect of varying the mostimportant model parameters on the resulting burst spectra, and we present a setof correlations among the spectral and temporal features of the bursts. Thespectral hardness, various spectral-temporal correlations and the spectralevolution of the simulated bursts are compared to those of observed bursts fora representative set of model parameters. Multi-pulse structures are simulatedusing a variable magnetic field and anisotropic emission, and the mostimportant spectral and temporal properties of these pulses are compared withobservations.Comment: AAS macro aaspp4.sty and psfig.tex (version 1.9) used, 19 pages and 7 figures, ApJ in press. Minor changes relative to the 2nd version. Most changes relative to the 1st version are in section 2 (analytic results