Speaker
Description
Pulse profiles provide a powerful diagnostic of the emission geometry and radiative processes in accreting X-ray pulsars, but their observed shape is affected by instrumental properties. We demonstrate that the energy-dependent pulsed fraction can be used as a robust timing cross-calibration diagnostic to combine XMM-Newton/EPIC-pn and NuSTAR observations. Using a simultaneous observation of the accreting pulsar Vela X-1, we show that once instrumental effects such as deadtime, energy redistribution, and source and background region selection are accounted for, the pulsed fraction measured by the two instruments can be consistently superimposed in their common energy range. This enables a seamless combination of XMM-Newton and NuSTAR data covering the 0.5–70 keV band. Residual differences around the iron-line region are attributed to the different energy resolutions of the instruments. Modelling the pulsed fraction obtained from the combined dataset reveals localized broad dips likely associated with cyclotron scattering features and soft X-ray emission lines. We further show that during orbital phases of reduced absorption, timing signatures of emission lines become more pronounced when spectral features are weak. This demonstrates that timing analysis is sensitive to scattering processes not always evident in energy spectra, highlighting its role as a powerful complement to spectroscopy.
