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We model the observed X-ray spectral continuum shape, ionic column densities,and absorption measure distribution (AMD) of the warm absorber in the Seyfertgalaxy NGC 3783. We assume a photo-ionized medium with a uniform total(gas+radiation) pressure. The irradiation causes the wind to be radiationpressure compressed (RPC). We compare the observational characteristics derivedfrom the 900 ksec Chandra observation to radiative transfer computations inpressure equilibrium using the radiative transfer code TITAN. We exploredifferent values of the ionization parameter xi of the incident flux and adjustthe hydrogen-equivalent column density, N_H0 of the warm absorber to match theobserved soft X-ray continuum. We derive theoretical column densities for abroad range of ionic species of iron and neon and an AMD that we compare to theobservations. We find an extension of the degeneracy between xi and N_H0 forthe constant pressure models previously discussed for NGC 3783. Including theionic column densities of iron and neon in the comparison between observationsand data we conclude that a range of ionization parameters between 4000 and8000 ergs cm/s is preferred. For the first time, we present theoretical AMD fora constant pressure wind in NGC 3783 that correctly reproduces the observedlevel and is in approximate agreement with the observational appearance of aninstability region. Using a variety of observational indicators, we confirmthat the X-ray outflow of NGC 3783 can be described as an RPC medium inpressure equilibrium. The observed AMD agrees with a uniformly hot or auniformly cold thermal state. The measured ionic column densities suggest thatthe wind tends to the uniformly cold thermal state. The occurrence of thermalinstability in the warm absorber model may depend on the computational methodand the spatial scale on which the radiative transfer is solved.

The thermal instability of the warm absorber in NGC 3783