χ²-contour-map (solid line: 68% confidence; dashed: 90%; dotted: 99%) between the fundamental CRSF energy, E_CRSF, 0, and its depth, τ_CRSF, 0, in epoch I (red) and epoch II (blue). The blue cross marks the best-fit values from epoch II with their respective uncertainties (see Table 1). The CRSF parameters found by Nakajima et al. (2006, Table 4; circles) and by Müller et al. (2013, Table 2; diamonds) are added for comparison. The filled symbols mark parameters obtained at a source luminosity similar to Epoch I and Epoch II.