MG11 
Talk detail
 

 Participant 

Institution

Session

Talk

Abstract

Theoretical interpretation of luminosity and spectral properties of GRB 031203

The X and gamma-ray observations of the source GRB 031203 by INTEGRAL are interpreted within our theoretical model. We specifically assume that the afterglow emission originates from a thermal spectrum in the co-moving frame of the expanding baryonic matter shell. By determining the two free parameters of the model and estimating the density and filamentary structure of the ISM, we reproduce the observed luminosity in the 20-200 keV energy band. As in previous sources, the prompt radiation is shown to coincide with the peak of the afterglow and the luminosity substructure are shown to originate in the filamentary structure of the ISM. We predict a clear hard-to-soft behavior in the instantaneous spectra. The time-integrated spectrum over 20 seconds observed by INTEGRAL is well fitted. Also, a possible interpretation of the connection between GRB 031203 and SN 2003lw will be outlined.

The fireshell model in the Swift era

We have recently obtained the exact analytic solutions of the relativistic equations relating the radial and time coordinate of a relativistic thin uniform shell expanding in the interstellar medium in the fully radiative and fully adiabatic regimes [ApJ 633 (2005) L13]. Applying these solutions to the Gamma-Ray Burst (GRB) afterglows, we determined the corresponding exact analytic expressions of the EQuiTemporal Surfaces (EQTSs) of the observed radiation [ApJ 620 (2005) L23]. Assuming that such radiation is not emitted in spherical symmetry but is confined into a narrow jet, we also determined the exact analytic expressions to compute the value of the detector arrival time at which we start to "see" the sides of the jet [ApJ, in press, astro-ph/0605332]. We compare and contrast these results with the corresponding approximate relations usually adopted in the GRB literature. The importance of using the exact solutions instead of the approximate ones in the interpretation of the Swift data is discussed.

Theoretical interpretation of "long" and "short" GRBs

The recent Swift and HETE-II observations of the afterglow of short GRBs set a new step toward understanding the uniqueness of our theoretically predicted Gamma-Ray Burst (GRB) structure as composed by a proper-GRB (P-GRB), emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the so called "prompt emission" as due to external shocks. The short GRBs are identified with the P-GRBs possibly followed by a small afterglow, while the long GRBs are identified with the afterglows with possibly a small precursor (the P-GRB). The role of the plasma baryon loading parameter in fixing the ratio between the P-GRB and the afterglow intensities, and therefore in discriminating between "short" and "long" GRBs, is discussed in the framework of our theoretical model.