Light curve and hardness evolution. Top panels: observed 0.5–7.0 keV X-ray light curves in cgs units (blue points), starting at T = 20 s. We also plot the best-fit broken power-law or simple power-law model (red solid lines). The light curves contain five counts per bin. Bottom panels: hardness ratio evolution (the soft and hard energy bands are 0.5–2.0 keV and 2.0–7.0 keV, respectively), following the Bayesian method of Park et al. (2006). The red dashed line denotes a hardness ratio equal to zero. Here, T₀ = 0 s is defined as the time when the count rate is 3σ higher than the Poisson background level.