Work

Kinematically Resolving the Fe K Complex in Her X-1: The Accretion Disk and Ionized Wind across X-Ray Eclipses

Year: 2026

Type: article

Abstract: We present the XRISM/Resolve spectroscopy of Her X-1 across three X-ray eclipses observed in 2024 September, resolving its iron K complex through the ingress, mid-eclipse, and egress phases. The 5 eV high energy resolution of Resolve enabled us to disentangle and detect all the primary components of the iron K complex: neutral iron fluorescence (Fe K α and K β ) and highly ionized emission lines (Fe XXV He α and Fe XXVI Ly α ). The neutral Fe K α emission is not significantly detected during mid-eclipse, indicating a compact origin near the neutron star. At ingress and egress, the line centroid exhibits red- and blueshifts of ∼200 km s −1 after correcting for the systemic velocity and the neutron star’s orbital motion. This residual shift corresponds to Keplerian rotation at a characteristic radius of r disk ∼ 6.6 × 10 6 km, suggesting an association with the outer accretion disk. In contrast, the highly ionized Fe XXV He α and Fe XXVI Ly α lines remain visible during eclipses, indicating an extended origin. Photoionization modeling (SPEX pion model) yields log 10 ( ξ / erg cm s − 1 ) ∼ 3.4 and N H ∼ 3.1 × 10 22 cm −2 , consistent with the ionized disk wind of Her X-1. Flux-ratio diagnostics constrain the geometric inner boundary of the clumpy disk wind to R in = 3 − 2 + 5 × 1 0 10 cm (1 σ ), consistent with the Compton-heated thermal winds. The inferred mass outflow rate is M ̇ out ≈ 3.2 × 1 0 − 9 M ⊙ yr − 1 (half the supplied mass), consistent with absorption line measurements of the disk wind obtained out of eclipse.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/ae96a7