Flux Dependence of the 1,keV Soft X-ray Feature in SAX J1808.4-3658 with NICER
Systematic X-ray spectral analysis of SAX J1808.4-3658 during 2019 and 2022 outbursts showed that a long-standing ~1 keV spectral feature varies with source brightness, strongly correlating with continuum and blackbody flux. This coupling establishes the feature's direct link to the accretion process, suggesting it is driven by changes in the inner accretion environment's density.