GHISELLINI G., GHIRLANDA G., MEREGHETTI S., BOSNJAK Z., TAVECCHIO F. and FIRMANI C.
Abstract (from CDS):
GRB980425 and GRB031203 are apparently two outliers with respect to the correlation between the isotropic equivalent energy Eisoemitted in the prompt radiation phase and the peak frequency Epeakof the spectrum in a νFνrepresentation (the so-called Amati relation). We discuss if these two bursts are really different from the others or if their location in the Eiso-Epeakplane is the result of other effects, such as viewing them off-axis, or through a scattering screen, or a misinterpretation of their spectral properties. The latter case seems particularly interesting after GRB060218 that, unlike GRB031203 and GRB980425, had a prompt emission detected both in hard and soft X-rays which lasted ∼2800s. This allowed us to determine its Epeakand total emitted energy. Although it shares with GRB031203 the total energetics, it is not an outlier with respect to the Amati correlation. We then investigate if a hard-to-soft spectral evolution in GRB031203 and GRB980425, consistent with all the observed properties, can give rise to a time-integrated spectrum with an Epeakconsistent with the Amati relation.