THE
COMPACTNESS PROBLEM IN GRBS
E. Lopez
Instituto
de Astronomia, Geofísica e Ciências Atmosféricas
Universidade
de São Paulo, Brasil
A generic scheme of a cosmological GRBs model
has emerged in the last few years. According to this scheme the observed
gamma-rays are emitted when an ultrarelativistic energy flow is converted into
radiation. Based in this interpretation
we review the problem of high opacity for the pairs e+e-, in both creation and
scattering processes. We show that the large opacity should be understood as a
natural consequence of the ultra-relativistic motion of the emitting plasma and
the beaming due to the special orientation of the jets pointing directly at us.
We show that the observed flux radiation in Blazars (GRBs) strongly depends on
the amount of relativistic beaming,as well as on the intrinsic properties of
the jet. Consequently, the required energy at the source for the gamma-burst
formation is of the order of the typical value for an galactic neutron star.
The analyze is carry out considering the observed flux density value of F ~
10^{-7} erg cm^{2} s^{-1}, the source position at an extragalactic distance and
the fact that the radiating plasma should be in laboratory frame optically
thin. On the other hand, we discuss briefly the controversial absorption
features observed by the Konus detector. Following the results that we have
derived previously in a radiation dispersion model for a relativistic moving
plasma, we have noted that the boosting on the resonance lines produced in the
emitting plasma which is aligned with the line of sight, can provide the
required shift on the resonance lines, so that their positions fall into the
observed frequencies in the range of ~ 20-60 keV.