Cyclotron lines in Vela X-1

The model in use is the Negative Positive EXponential (NPEX) model (with Gamma_2_ always fixed to -2, Mihara, 1995, Ph.D. Thesis, Riken, Tokyo) modified by photoelectric absorption, an additive iron line at ~6.4keV, and none, one, or two cyclotron resonant scattering features (CRSF)s at ~25 and ~50keV. The phase bins for the 2000 observation are: - rise, center, and fall of the main pulse - rise part 1, rise part 2, center, and fall of the secondary pulse - the two inter pulse phases The phase bins for the 1998 observation are: - rise and fall of the main pulse - rise and fall of the secondary pulse - the two inter pulse phases