GRB 060218 and the binaries as progenitors of GRB-SN systems

Abstract

(shortened) We study the Gamma-Ray Burst (GRB) 060218: a particularly close source at z=0.033 with an extremely long duration, namely T_{90} ~ 2000 s, related to SN 2006aj. [...] I present the fitting time consuming procedure. In order to show its sensitivity I also present two examples of fits with the same value of B and different value of E_{e^\pm}^{tot}. We fit the X- and \gamma-ray observations by Swift of GRB 060218 in the 0.1-150 keV energy band during the entire time of observations from 0 all the way to 10^6 s within a unified theoretical model. The free parameters of our theory are only three, namely the total energy E_{e\pm}^{tot} of the e^\pm plasma, its baryon loading B \equiv M_Bc^2/E_{e\pm}^{tot}, as well as the CircumBurst Medium (CBM) distribution. We justify the extremely long duration of this GRB by a total energy E_{e\pm}^{tot} = 2.32\times 10^{50} erg, a very high value of the baryon loading B=1.0\times 10^{-2} and the effective CircumBurst Medium (CBM) density which shows a radial dependence n_{cbm} \propto r^{-\alpha} with 1.0 \leq \alpha \leq 1.7 and monotonically decreases from 1 to $10^{-6}$ particles/cm$^3$. We recall that this value of the $B$ parameter is the highest among the sources we have analyzed and it is very close to its absolute upper limit expected. [...] We also think that the smallest possible black hole, formed by the gravitational collapse of a neutron star in a binary system, is consistent with the especially low energetics of the class of GRBs associated with SNe Ib/c.