The thermal instability of the warm absorber in NGC 3783

Abstract

We model the observed X-ray spectral continuum shape, ionic column densities, and absorption measure distribution (AMD) of the warm absorber in the Seyfert galaxy NGC 3783. We assume a photo-ionized medium with a uniform total (gas+radiation) pressure. The irradiation causes the wind to be radiation pressure compressed (RPC). We compare the observational characteristics derived from the 900 ksec Chandra observation to radiative transfer computations in pressure equilibrium using the radiative transfer code TITAN. We explore different values of the ionization parameter xi of the incident flux and adjust the hydrogen-equivalent column density, N_H0 of the warm absorber to match the observed soft X-ray continuum. We derive theoretical column densities for a broad range of ionic species of iron and neon and an AMD that we compare to the observations. We find an extension of the degeneracy between xi and N_H0 for the constant pressure models previously discussed for NGC 3783. Including the ionic column densities of iron and neon in the comparison between observations and data we conclude that a range of ionization parameters between 4000 and 8000 ergs cm/s is preferred. For the first time, we present theoretical AMD for a constant pressure wind in NGC 3783 that correctly reproduces the observed level and is in approximate agreement with the observational appearance of an instability region. Using a variety of observational indicators, we confirm that the X-ray outflow of NGC 3783 can be described as an RPC medium in pressure equilibrium. The observed AMD agrees with a uniformly hot or a uniformly cold thermal state. The measured ionic column densities suggest that the wind tends to the uniformly cold thermal state. The occurrence of thermal instability in the warm absorber model may depend on the computational method and the spatial scale on which the radiative transfer is solved.

accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (14)

• Chasing obscuration in type-I AGN: discovery of an eclipsing clumpy wind at the outer broad-line region of NGC 3783
• Thermally driven wind as the origin of warm absorbers in AGN
• Multiphase AGN winds from X-ray irradiated disk atmospheres
• Multi-wavelength campaign on NGC 7469: III. Spectral energy distribution and the AGN wind photoionisation modelling, plus detection of diffuse X-rays from the starburst with Chandra HETGS
• Photoionized emission and absorption features in the high-resolution X-ray spectra of NGC 3783
• Magnetized Disk-Winds in NGC 3783
• Evidence for Radiation Pressure Compression in the X-ray Narrow Line Region of Seyfert galaxies
• Spectral and polarization properties of reflected X-ray emission from black hole accretion discs
• What shapes the Absorption Measure Distribution in AGN outflows
• Warm Absorber Diagnostics of AGN Dynamics
• Time-dependent photoionization spectroscopy of the Seyfert galaxy NGC 3783
• Joint Fit of Warm Absorbers in COS & HETG Spectra of NGC 3783
• Active Galactic Nuclei and their demography through cosmic time
• A constant pressure model for the warm absorber in Mrk 509