Spectral model polcap for different magnetic field strengths. The magnetic field strengths are varied for cyclotron energies between 50–80 keV in the NS frame. The X-ray spectra are shown in the observer’s frame. The colored dashed lines indicate the cyclotron energy in the observer’s frame. The green line shows the NuSTAR effective area for a source region with 30″ diameter and 1′ off-axis angle.