Dynamical and radiative evolution of a fireball

In chapter 2 we introduce the observational properties of GRBs and afterglows, describing the main features of these events and summarizing the currently proposed interpretations within the framework of the fireball model. In chapter 3 we introduce the complete theoretical treatment of the hydrodynamics of a spherical fireball and the whole set of analytical approximations we have derived and used (sections from 3.2 to 3.5), the general procedure for the detailed calculation of afterglow light curves and spectra (section 3.6) and of the comoving emissivity of shocked matter according to the theory of synchrotron radiation and the fireball hydrodynamics (sections 3.7 and 3.8). The anisotropic fireball model we have developed, based on spherical hydrodynamics with a direction dependent baryon loading, is introduced in chapter 4. Finally, in chapter 5 we present the results of the calculation of afterglows and spectra from spherical fireballs with intrinsic parameters varying in the range required for building an anisotropic fireball. After presenting (standard) approximated predictions about afterglows from spherical fireballs (section 5.2), we show the results of calculations performed neglecting the cooling of emitting electrons (section 5.3.1), and then the results of calculations performed taking into account the cooling of electrons (section 5.3.2).