XRISM Spectroscopy of Variable Accretion-driven Disk Winds in NGC 4151 When, Where, and How Fast Outflows are Launched

X-ray observations probe the inner accretion flow within active galactic nuclei, revealing the highest gas column densities and fastest winds. The most diverse winds yet revealed with the Resolve calorimeter spectrometer aboard XRISM are found in NGC 4151, a nearby Seyfert 1 active galactic nucleus (AGN) that may qualify as a changing-look source (CLAGN). Herein, we report on wind variability in 14 XRISM observations of NGC 4151, summing to 0.9 Ms of exposure over a period of 395 days. We examined the dependence of key wind parameters on hardness and intensity selections, and as a function of time relative to flaring and dip events. The results suggest a globally organized but locally complex wind structure. Slow “warm absorber” components (WAs; v_out ∼ 100–1000 km s⁻¹) are always observed and likely represent failed winds at radii of 10⁴–10⁵GM/c² within the inner wall of the torus. In contrast, “very fast” and “ultrafast” outflows (VFOs and UFOs; v_out ∼ 10³–10⁴ km s⁻¹ and v_out ∼ 0.033–0.33c, respectively) are strongest 10 ks after the peak of flares and during periods with low flux. Ten kiloseconds is among the shortest flare–wind response timescales reported in an AGN, suggesting that the winds are observed close to the launching site. The absorption measure distribution (AMD) and the large outflow momentum rates suggest that the high-velocity flows visible in the Fe K band are magnetically driven, while locally clumpy, likely owing to radiation pressure; one or both of these mechanisms may be enhanced following a flare and be most visible during low-flux windows.