2026ApJ...999..133S

We report on our investigation of the NuSTAR and AstroSat observations along with simultaneous NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4-3658, obtained during its tenth outburst from 2022. The NuSTAR observation captured the source near the outburst peak, while AstroSat observed it during the decay phase. Coherent pulsations at ∼401 Hz were detected throughout the outburst, with the fundamental amplitude in the 3-30 keV range increasing from ∼4% near the peak to ∼6% during the decay. The pulsations display strong energy dependence and negative time lags of ∼0.2-0.3 ms, with harder photons leading softer ones. The broadband spectra in both epochs are well described by a soft thermal component and Comptonized continuum, together with a prominent relativistic reflection component. As the outburst evolved, the continuum softened (Γ increasing from ∼1.88 to ∼1.99) and the coronal electron temperature decreased (kT_e from ∼31 to ∼18 keV), consistent with enhanced Compton cooling at lower accretion rates. The ionization parameter declined ($\mathrm{log}\xi $ from ∼3.4 to ∼1.8) while the reflection fraction increased, suggesting a changing accretion geometry with a more compact corona and a larger disk covering fraction during the decay phase. The X-ray luminosity decreased by a factor of ∼3 between the two epochs. Our results suggest the coupled evolution of the corona, disk, and magnetosphere as the mass accretion rate declines.