tokens: is time independent. This is the case for GRB 160625B as presented in the right panel of Figure 8 . Moreover, typically is observed to increase over a pulse (Ryde Pe’er 2009 ); this is the case for most bursts in our sample, with two prominent cases of GRB 140329B and GRB 150330A. To derive the parameters in the rest frame, the selected bursts should have known redshift. A redshift measurement of 2.73 is found for GRB 140206B (Malesani et al. 2014 ), and 1.406 for GRB 160625B (Zhang et al. 2018 ). However, GRB 140329B and GRB 150330A are without known redshift. On the other hand, Iyyani et al. ( 2013 ) investigated how the different values of redshift affect the results and pointed out that, for different values of z , the estimated outflow parameters change within a factor, but the time evolution of the behavior of the parameters remains the same. We therefore assume an average value of GRBs (Bagoly et al. 2006 ), z = 2, for the calculation (see also Iyyani et al. 2013 ). 3.1.3. Lorentz Factor, Γ The coasting values of the Lorentz factor ( r ph > r s ) are derived by (see also Equation (4) in Pe’er et al. 2007 )where Y is the ratio of total fireball energy to the energy emitted in gamma-rays. As depicted in Figure 9 , temporal evolution of the Lorentz factor shows either an approximately constant (e.g., GRB 140206B) or a monotonic decay behavior (e.g., GRB 140329B exhibits a monotonic decline throughout the pulse), or both (initially approximately constant and then decaying faster, e.g., GRB 150330A, GRB 160625B). The best fitting gives power-law indices of 0.01 ± 0.07 for GRB 140206B and −0.51 ±0.03 for GRB 140329B. We fit GRB 150330A and GRB 160625B with a smoothly broken power-law function, which gives best-fitting power-law indices of 0.69 ± 0.52 (before the break) and −0.52 ± 1.44 (after the break) for GRB 150330A and 0.37 ± 0.27 (before the break) and −0.89 ± 0.33 (after the break) for GRB 160625B. Figure 9. Temporal evolution of the Lorentz factor, Γ. Color conventions are the same as in Figure 8 . GRB 140206B presents a constant behavior with best-fitting power-law index 0.01 ± 0.07, while GRB 140329B shows monotonic decay with index −0.51 ± 0.03. GRB 150330A and GRB 160625B exhibit a smoothly broken power-law decay feature, with power-law indices 0.69 ± 0.52 and −0.52 ± 1.44 before and after break for GRB 150330A and 0.37 ± 0.27 and −0.89 ± 0.33 before and after break for GRB 160625B. The global view on the evolution of the Lorentz factor decays with time from a few hundred Y 1/4 down to below 100 Y 1/4 (e.g., Fan Wei 2011 ; Peng et al. 2014 ). The decreasing Lorentz factor may have several implications (Iyyani et al. 2013 ). Since typically is observed to increase over a pulse, the decrease of the values of Γ = Γ( t ) is not surprising by realizing the fact that ; such a decrease must, therefore, be a common characteristic form over individual pulse structures in GRBs (Ryde Pe’er 2009 ). This is because, during the rising
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