On the physical processes which lie at the bases of time variability of GRBs

The relative-space-time-transformation (RSTT) paradigm and tire interpretat ion of the burst-structure (IBS) paradigm are applied to probe the origin o f the time variability of GRBs. Again GRB 991216 is used as a prototypical case, thanks to the precise data from the CGRO, RXTE: and Chandra satellite s. It is found that with the exception of the relatively. inconspicuous but scientifically very important signal originating from the initial "proper gamma ray burst" (P-GRB), all the other spikes and time variabilities call be explained by the interaction of the accelerated-baryonic-matter pulse wi th inhomogeneities in the interstellar matter. This call be demonstrated by using the RSTT paradigm as well as the IBS paradigm, to trace a typical sp ike observed in arrival time back to the corresponding one ill the laborato ry time. Using these paradigms, the identification of tire physical nature of the time variablity of the GRBs carl be made most convincingly. It is ma de explicit the dependence of a) the intensities of the afterglow, b) the s pikes amplitude and c) the actual time structure on the Lorentz gamma facto r of the accelerated-baryonic-matter pulse. In principle it is possible to read off from the spike structure the detailed density contrast of the inte rstellar medium in the host galaxy, even at very high redshift.