The rise and decline of a transient obscuration event in a moderately distant type-I quasar

Outflows of ionised material, often dubbed warm absorbers (WAs), are common in nearby Seyferts but sparse in distant and more energetic quasars (QSOs). This paper presents multi‑epoch X‑ray and optical observations of the serendipitously identified type-I QSO 2MASS,J14302580+4159572 at a moderate redshift of z = 0.35, which trace the rare case of the rise and decline of a transient ionised absorber over a 22-year timescale. The discovery observations were carried out by between 2002 and 2005. The first two (2002 and 2003) show unremarkable X-ray spectra typical of unobscured type-I QSOs. The third observation in 2005, however, reveals a pronounced suppression of the X-ray spectrum at energies below sim3,̊m keV. Spectral analysis demonstrates that the 2005 event is produced by a moderately ionised absorber with column density N_H ,̊m cm^ and ionisation parameter ̊m log,ξ , . Corroborating this picture, the high-ionisation 22 -2 Simultaneous X-ray data analysis of νstar, and data over a 22‑year baseline indicates that the absorber remains stable for nearly 18 years before weakening in the 2023-2024 observations. Throughout this period, the intrinsic 3--10,keV continuum remains remarkably stable, confirming that the variability is driven by evolving line‑of‑sight ionised absorption rather than intrinsic luminosity fluctuations. We interpret the event as a thermally driven ionised outflow located outside the broad-line region (BLR) at sub‑parsec to parsec distances with an estimated density of about 10^ 6 cm^ -3 O,III łambda4363 line in the optical spectra vary in tandem with the X-ray absorption, suggesting that the outflow progressively modifies the ionisation state of the inner narrow-line region (NLR) on decadal timescales.