Nominal fit to the candidate transit event of Proxima Centauri b. The observed flux is normalized by the predicted flux from GP regression. The best-fitted transit model (red solid line) yields T_C = 2,457,640.1990 ± 0.0017 HJD (the vertical red dashed line), T_d = 82.6 ± 5.3 minutes, and D = 5.2 ± 1.0 mmag for GP regression using the Matérn 3/2 kernel, while T_C = 2,457,640.1990 ± 0.0017 HJD, T_d = 82.7 ± 5.3 minutes, and D = 5.2 ± 1.0 mmag for GP regression using the Squared Exponential kernel. The dashed lines and dotted lines are the 1σ and 2σ confidence regions of the GP regressions, respectively.