Photometry and physical characterization of near-Earth asteroid 2025 FA22 from one apparition

We present comprehensive photometric characterisation of 2025 FA22, a Potentially Hazardous Asteroid (PHA) discovered on 29 March 2025 and observed during the seventh International Asteroid Warning Network (IAWN) coordinated campaign. The asteroid’s close approach at 2 lunar distances on 18 September 2025 provided an opportunity for rapid physical characterisation in a simulated virtual impactor scenario. Photometric observations were conducted from 17 September to 1 October 2025, during which 2025 FA22 traversed a 150○ arc and spanned solar phase angles from ∼20○ to ∼70○. This geometry enabled detailed physical characterisation, including determination of the spin axis and shape. Convex inversion yields a sidereal rotation period of Psid = 13.07366 ± 0.00076 h and a spin axis at ecliptic coordinates (λ, β) = (246○ ± 9○, 60○ ± 9○). The absolute magnitude was derived as HV = 21.39+0.07-0.08 mag (G1 = 0.8228, G2 = 0.0194), with colour indices B − V = 0.71 ± 0.05 mag, V − R = 0.39 ± 0.03 mag, and R − I = 0.39 ± 0.04 mag, consistent with X-complex classification in the Bus–DeMeo taxonomy. Assuming a geometric albedo of pᵥ = 0.15+0.05-0.04, representative of the moderate-albedo X-complex asteroids, we estimate Deff = 181⁺³¹₋₂₅ m, consistent with “China Compound Eye” radar dimensions of ∼100 × 320 m (Deff ∼ 186 m), which also reveal a contact-binary morphology consistent with the axis ratios a: b: c ∼ 2.68 : 1.96 : 1.00 derived from our photometric shape model. The bilobate morphology is consistent with YORP-driven spin-up and deformation during a previous YORP cycle, with the current slow rotation possibly explained by internal reconfiguration or tidal braking during close Earth encounters.