Speaker
Description
The spectral emission of accreting X-ray pulsars is complex due to their non-isotropic nature and the inclination of the line of sight with respect to the geometry of the system, which influences the observed phase variability at the spin frequency. Recently, Ferrigno et al. (2023) introduced a method to compute pulsed profiles with the energy resolution of the NuSTAR satellite, enabling detailed analysis of the Pulsed Fraction (PF) across different energy bands. This approach revealed Gaussian-like features in the PF, corresponding to well-known spectral signatures, such as the iron fluorescence line and cyclotron resonance scattering features (CRSFs), superimposed on an increasing trend of PF values with energy.
I applied the Ferrigno et al. method to four NuSTAR observations of the HMXB 4U 1901+03 during its 2019 Type II outburst. By analyzing the energy- and phase-resolved PF spectra, I explored the evolution of the pulsed fraction and harmonic content with the source's luminosity state. Observations near the outburst peak exhibit similar spectral properties, as do those taken during the descending phase, where the luminosity is significantly lower. The synergy between PF spectrum analysis, harmonic content, and phase-resolved spectra sheds light on the variability of the CRSF and its correlation with luminosity and phase.