Example of a spectral modeling for continuum plus cyclotron lines. Reproduction of Fig. 2 of Pottschmidt et al. (2005), showing the phase averaged spectrum of V 0332+53 as observed with RXTE for a Fermi–Dirac continuum and up to three cyclotron lines (modeled using the Gaussian optical depth profile gabs). Panel a: combined PCA/HEXTE spectrum (crosses), best-fit model (histogram), and unfolded spectrum (dotted and solid lines, right y-axis label), illustrating the cumulative effect of the CRSFs on the continuum. Panels b–f: residuals for models taking increasing numbers of CRSFs into account: panel b: no line; panel c: one line at 25.5 keV; panel d: two lines, at 25.6 keV and at 50 keV; panel e: two lines: the fundamental line modeled by two Gaussian components at 25.2 keV and 26.6 keV, and its harmonic at 49.9 keV; panel f: three lines, the fundamental modeled by two components at ∼25 keV and ∼27 keV and two harmonics at ∼51 keV and at ∼74 keV. For further explanation see Pottschmidt et al. (2005).