THE VELOCITY VARIATION OF INTERNAL SHOCK IN GRB

With the BATSE TTS model data, the work analyzed the sub-pulse width and the time lag between high and low energy band of GRB960113, which is in simple shape and good SNR. The result shows that the lags and widths increase and broaden monotonously with time. In the general views, the internal shock is produced by collision of shells with random Lorentz factors. Here, a special picture is considered, i.e., an extremely relativistic shell from the center catches up and collides with the outer slow shells successively, it produces the Gamma-ray emission, then the fast shell slow down. After collision, the Lorentz factor of the slow shell is basically in direct proportion to that of the quick one. Therefore, the variation of Gamma ray emission can reflect the change of the velocity of the fast shell. From the relation $\frac{\gamma_j}{\gamma_i}=\frac{\Delta t_i}{\Delta t_j}$（where γ_i is the Lorentz factor of pulse i, △t_i is the time lag of pulse i observed in the rest frame）, the decrease of γ necessarily induces the increase of △t. The variances in GRB960113 is consistent with such case. If the Gamma rays are produced with an internal shock, the result shows that there is velocity variation of internal shock. The work also calculates the time lag of every sub-pulse of 88 GRBs in TTS data. Majority is high-energy photons leading; the distribution has a peak around -25 ms. This paper has advanced a new idea in using the BATSE TTS data to produce light curves with 8 ms time resolution. This is as opposed to the usual 64 ms resolution used by all previous studies. This is an improvement that will substantially help with measuring the lags for the highest luminosity bursts which have lags shorter than 64 ms.