1. Lecture 4:
Light extinction:
Compton scattering
Gamma-Ray Bursts

2. GRBs are brief flashes of soft -ray radiation (100 keV), discovered in the 1970’s, the origin of which was not known
until 1997
CGRO-BATSE

3. Compton thick sources
In Seyfert 2 galaxies there is evidence of cold material around the nucleus and of absorption caused by this material in excess of the Galactic one. The local column density of this material is optically thick to Compton scattering
Bassani et al. 1999, ApJS, 121, 473
Matt et al. 1999, New Astronomy, 4, 191

4. Compton-thick sources

5. CGRO spectrum of a GRB

6. relativistic conditions are implied: Lorentz factor 
CGRO-BATSE (Fishman & Meegan 1995)
Light curves of GRBs
Fluence ~
if cosmological
relativistic conditions
are implied:
Lorentz factor 

7. The GRB distribution is isotropic