Gamma-ray burst phenomenology explained through the blast wave model

The essential physics of the blast wave model is contained in a formula recently proposed to describe the temporal evolution of the nonthermal synchrotron spectra from gamma-ray bursts (GRBs). This formula accounts for many of the well-established empirical trends in GRB physics, including the basic form of the fast-rise, gentle-decay FRED-type GRB light curves, the characteristic hard-to-soft spectral evolution and intensity-hardness correlations of GRB light curves, and the recently uncovered relations between the nu F(nu) peak energies and the photon and energy fluences. On the basis of this formula, we predict the tendency for pulses to align at high energies and to lag at low energies. The overall GRB duration distribution is understood when triggering properties of GRB detectors are considered for fireballs with a range of baryon loading parameters. The existence of new classes of clean and dirty fireballs are implied. Short timescale variability of GRB light curves is attributed to density variations in the circumburster medium (CBM).