Thursday, 11 March 2004 - h. 15:00 

Auditorium B. Touschek


G. Barbiellini

(Trieste Univ.)

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 GRB energetic.
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.


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MCD, 19/2/2004