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).
