Double-hump spectrum, pulse profile dip, and pulsed fraction spectra from the low-accretion regime in the X-ray pulsar

Accreting X-ray pulsars (XRPs) undergo different physical regimes depending on different mass accretion rates, with related changes in the emitted X-ray spectral properties. Recent observations have shown a dramatic change in the emission properties of this class of sources observed at low luminosity. We explore the timing and spectral properties of the XRP observed in the low-luminosity regime (about 5, erg, s) to witness the corresponding spectral shape and pulse profiles. 33 -1 We employed recent and mathrm and νstar pointed observations of the X-ray activity during the low-luminosity stage. We explored several spectral models to fit the data and test theoretical expectations of the dramatic transition of the spectral shape compared to the higher luminosity regime. We studied the pulsating nature of the source and found a precise timing solution. We explored the energy-resolved pulse profiles and the derived energy dependence of different pulsed fraction estimators (mathrm PF_ minmax PF_ rms). We also obtained νstar pulsed fraction spectra (PFS) at different luminosity regimes. The spectrum is well fit by a double Comptonization model, in agreement with recent observational results and theoretical expectations that explain the observed spectrum as being composed of two distinct bumps, each dominated by different polarization modes. We measured a spin period of 1081. 86 remains steady at sim60%. The PFS obtained at high luminosity shows evidence of an iron Kα emission line but no indications of a cyclotron line. consistent with the source spinning up compared to previous observations, yielding an upper limit for the magnetic field strength of Błesssim9, G. The pulse profiles show a single broad peak interrupted by a sharp dip that coincides with an increase in the hardness ratio, and thus likely due to absorption. For the low-luminosity observation, the mathrm increases with energy up to sim100% in the 10-30 keV band, while the mathrm 13 PF_ minmax PF_ rms