  We study experimentally superradiant Rayleigh scattering from a Bose-Einstein
condensate (BEC) in a new parameter regime where pump depletion and the
exchange of photons between the endfire modes are important. Through
experiments and simulations we show that collective atom light coupling leads
to the self-organized formation of dynamic Bragg gratings within the sample.
These gratings lead to an efficient back-scattering of pump photons and optical
resonator structures within the BEC.
