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

TL;DR

This paper models GRB 060218's long duration and low energy using a unified theoretical framework, highlighting the role of binary systems and specific physical parameters in GRB-SN progenitors.

Contribution

It introduces a detailed fitting procedure for GRB 060218's observations with a minimal parameter set, emphasizing the importance of binary progenitors in GRB-SN systems.

Findings

The GRB's long duration is explained by specific energy and baryon loading values.

The CircumBurst Medium density decreases radially, affecting the burst's evolution.

The low energetics supports the hypothesis of neutron star collapse in binary systems as progenitors.

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.