出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We estimate the bulk Lorentz factor G0 of 31 GRBs using the measured peak time of their afterglow light curves and considering a homogeneous circumburst medium or a wind density profile. The values of G0 are distributed between few tens and several hundreds with average values 138 and 66 for the homogeneous and wind density profile, respectively. The isotropic energy and luminosity correlate in a similar way with G0, i.e. EisoµG0 2 and LisoµG0 2, while the peak energy EpµG0. These correlations are less scattered in the wind density profile than in the homogeneous case. We then study the energetics, luminosities and spectral properties of our bursts in their comoving frame. The distribution of L0 iso is very narrow with a dispersion of less than a decade in the wind case, clustering around L0 iso51048 erg s1. Peak photon energies cluster around E0 p 6 keV. The newly found correlations involving G0 allow us to interpret the EpEiso and EpLiso correlations as due to the different G0 factors and the collimation–corrected correlation, Ep Eg (obtained by correcting the isotropic quantities for the jet opening angle qj), can be explained if q2 j G0 = constant. Assuming the Ep Eg correlation as valid, we find a typical value of qjG0 6–20, in agreement with the predictions of magnetically accelerated jet models.
