Luminosity dependence of the cyclotron line energy. The black circles and green diamond denote RXTE measurements from Caballero et al. (2007) and Terada et al. (2006), respectively, while the red crosses show the NuSTAR results. The continuum models used to measure the line energy are CutoffPL and PLCUT for Obs. I and Obs. II, respectively. For Obs. II, we used the result of the fit with the PLCUT model. The PLCUT and CutoffPL + Gauss models result in consistent values for E_CRSF; however, this value is better constrained in the PLCUT case (Figs. 6 and 7). Terada et al. (2006) and Caballero et al. (2007) used the NPEX and CutoffPL model, respectively.