  The temporal structure of Gamma Ray Bursts can be interpreted assuming as a
inner engine a neutron star which undergoes a progressive compactification via
production of strangeness (hyperons and kaons) and quarks. We will propose a
tentative identification of various emission periods of the burst with specific
structural changes of the star. Each of these modifications of the composition
of the compact star takes place as a deflagration and not as a detonation, so
the energy released in the transition goes mainly into heat and not into a
mechanical wave. This is important in order to avoid an excessive baryonic
contamination of the region surrounding the compact star. In this way a
ultrarelativistic plasma of electron-positron pairs and of photons can be
obtained, powering the Gamma Ray Burst.
