A constant pressure model for the warm absorber in Mrk 509

Context. We present the analysis of 900 ks high-resolution RGS XMM-Newton observations of the nearby Seyfert galaxy Mrk 509 with the use of a self-consistent warm absorber (WA) model. We took a physically motivated approach to the modeling of the WA as a stratified medium in a constant total pressure (CTP) regime. Aims. Powerful outflows are fundamental ingredients of any active galactic nucleus (AGN) structure. They can significantly affect the cosmological environment of their host galaxy. High-resolution X-ray data are best suited for outflow’s studies, and the observed absorption lines on heavy elements are evidence of the physical properties of an absorbing gas. Our models allow us to fit continuum shapes bounded together with the line profiles, which gives additional constraints on the gas structure of WA in this source. In this work, we benchmark and test the CTP model on the soft X-ray spectrum of Mrk 509. Methods. A grid of synthetic absorbed spectra was computed with the photoionization code TITAN assuming that the system was under CTP. As an illuminating spectral energy distribution (SED), we used the most actual multiwavelength observations available for Mrk 509. We applied these models to the high-resolution spectrum of the WA in the Mrk 509, taking into account cold, warm and hot Galactic absorption on the way to the observer. Results. The constant total pressure gas with log ξ0 ∼ 1.9, defined on the cloud surface, fits the data well. A higher ionization component is needed for Ne X absorption. The best-fit model is optically thin with log NH = 20.456 ± 0.016. The lines are non-saturated, and the CTP spectral fit aligns with previous analyses of Mrk 509 with a constant density WA. The model constrains the gas density, placing the WA cloud at 0.02 pc, consistent with the inner broad line region and the thickening region of the accretion disk.