Speaker
Description
Pulse profiles of X-ray pulsars are invaluable tools for understanding emission mechanisms, system geometry, and radiation transfer under extreme conditions. By extracting energy-dependent pulse profiles Ferrigno (2023) showed how the changes in the pulse shape at energies corresponding to the cyclotron resonance scattering features, provide a quantitative way of determining the feature main properties (e.g. position and spectral width) with the same relative uncertainty given by the usual tools of spectral analysis. In this contribution, I will show how the application of the same method to the accreting source V0332+53 yields surprising results regarding the shape of its broad cyclotron feature. We studied the pulsed fraction spectra for all the available NuSTAR observations, thus sampling source luminosities different by a factor more than 30. We found some common key characteristics: a two-hump continuum with a local minimum around 10 keV, a double-peaked feature at the fundamental cyclotron energy, and a clear lag discontinuity at the same energies. The interpretation of such results leads to new clues for the spectral modelling of cyclotron features by using physical models to better constrain the plasma conditions of the emergent cyclotron feature.
