Top panel: Fermi-LAT light-curve of the flare phase with 3 hr binning. Flaring peaks were fitted by the F function (in Equation (5) for nine structures. Fits were performed in the MJD 56815.625–56835.130 time range. The thin color lines correspond to the contribution of single peaks in the total fit, which is represented by the thick black line. The dashed brown line is the fitted constant baseline, which also contributes to the total fit. Six major peaks were labeled for more detailed studies. The red arrows indicate the arrival time of the three high-energy photons used to calculate the Doppler factor in Section 5, and whose energies are labeled in the bottom panel. Due to an instrumental problem, the MJD 56834.375 bin contains no data. Middle panel: photon spectral index (Γ) of the PL fits of data. Bottom panel: arrival time and energy of E > 10 GeV photons with three different significance levels of source association (2-, 3-, and 4-σ Gaussian equivalent). This panel is a zoom of the bottom panel of Figure 1. Vertical red dash lines indicate the two major flaring phases (I and II), and black dotted lines indicate Peaks 2, 3, 4, and 5.