L. Izzo, R. Ruffini, A. V. Penacchioni, C. L. Bianco, L. Caito, S. K. Chakrabarti, Jorge A. Rueda, A. Nandi, B. Patricelli
The joint X and gamma-ray observations of GRB 090618 by a large number of
satellites offer an unprecedented possibility of testing crucial aspects of
theoretical models. In particular, it allows us to test (a) the formation of an
optically thick e+e- baryon plasma self-accelerating to Lorentz factors in the
range 200 < g < 3000; (b) its transparency condition with the emission of a
component of 10^{53-54} baryons in the TeV region and (c) the collision of
these baryons with the circumburst medium clouds, characterized by dimensions
of 10^{15-16} cm. In addition, these observations offer the possibility of
testing a new understanding of the thermal and power-law components in the
early phase of this GRB. We test the fireshell model of GRBs in one of the
closest (z = 0.54) and most energetic (Eiso = 2.90 x 10^{53} ergs) GRBs, namely
GRB 090618. We analyze its emission using several spectral models, with special
attention to the thermal and power-law components. We determine the fundamental
parameters of a canonical GRB within the context of the fireshell model. We
find evidences of the existence of two different episodes in GRB 090618. The
first episode lasts 50 s and is characterized by a spectrum consisting of
thermal component, which evolves between kT = 54 keV and kT = 12 keV. The
second episode, which lasts for \sim 100s, behaves as a canonical long GRB with
a Lorentz gamma factor at transparency of g = 495, a temperature at
transparency of 29.22 keV and with characteristic masses of the surrounding
clouds of \sim 10^{22-24} g. We support the recently proposed two-component
nature of GRB 090618 by using specific theoretical analysis and illustrate that
the episode 1 cannot be considered to be either a GRB or a part of a GRB event,
but it appears to be related to the progenitor of the collapsing bare core
leading to the formation of the black hole which we call a proto-black hole.
View original:
http://arxiv.org/abs/1202.4374
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