GRB: a luminous candle?
Few hundred (400) BATSE detected GRBs ordered by their fluence
values have been analysed in search of the signal from the Compton
echo. The signal has been detected on the sum of many GRB with a
statistical significance of 6 sigma.
The ratio of the prompt photons to reprocessed ones allows the
determination of the amount of material surrounding the central engine.
The time distribution of the Compton photons is linked to the
geometry of the reprocessing material. The prompt component
is exponentially attenuated by this material. Introducing a
correction for the attenuation the dispersion on the energetic of the
GRB is on average strongly reduced.
The experimental observation of the Compton echo is a new and important
step on the increasing evidence for a quite narrow dispersion on the
The possibility for future detectors to allow the attenuation
correction on the single GRB basis opens the prospective for exciting
observation of the cosmological relation luminosity versus red
shift in the region of z>1 where different cosmological models
show the strongest difference.