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New clues for constraining fireshell dynamics from high-energy GRBs

The canonical GRB is composed by three different components: the P-GRB emitted when the self-accelerating electron-positron plasma reaches the transparency, the prompt radiation emitted by the collision of baryon with the CircumBurst medium and a plateau-late afterglow phase. This third component has been fitted by synchrotron spectra and requires a process of energy injection. Following a framework delineated by Rees and Meszaros, we examine the possibility that a slower component in the self-accelerating electron-positron plasma collides with the accelerated baryon component, when their Lorentz factor decelerates by the interaction with the CircumBurst medium, giving the residual emission observed. In particular the cases of three high-energy GRBs, 061007, 080916c and 090423, are presented.

GRB 090423 : a canonical GRB at redshift z = 8.1

GRB090423 is the most distant GRB ever observed, with redshift z of about 8.1, a T90 duration is of 12 +- 1.2 s and an estimated Peak Energy of 40 +- 6 keV. We analyze Swift-BAT data in the band 15-150 keV and XRT data in the band 0.2-10 keV within the "fireshell" model. We can fit the source, for a total energy of the dyadosphere of 3.80 x 10^53 ergs, with a gravitational collapse to a ˜ 20 solar mass black hole. Possible solutions for such an e+e- black holes ranges from Mu = 1-50 solar masses for values of xi ranging from 0.15 to 0.88. Among these different Mu and xi we select one with Mu = 20 solar masses, and the corresponding xi = 0.233. We obtain an initial Lorentz gamma factor of 960 and a CBM average density in the range n = 10^-1 particles/cm^3 up to size of 10^18 cm, that corresponds to 1 light year. The conclusions are that this collapse occurred from a star by an almost complete gravitational collapse without any remnant up to a size of 1 light year. This is very different from all the other GRBs observed at smaller z factor, where an agreement with binary neutron stars or neutron stars / white dwarfs is possible.

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