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We present a detailed analysis of the Chandra High Energy Transmission Grating Spectrometer (HETGS) and XMM-Newton high-resolution spectra of the bright Seyfert 1 galaxy, Mrk 290.

The Chandra HETGS spectra reveal complex absorption features that can be best described by a combination of three ionized absorbers. The outflow velocities of these warm absorbers are about 450 km/s, consistent with the three absorption components found in a previous far-UV study. The ionizing continuum of Mrk 290 fluctuated by a factor of 1.4 during Chandra observations on a time-scale of 17 d. Using the response in opacity of the three absorbers to this fluctuation, we put a lower limit on the distance from the ionizing source of 0.9 pc for the medium ionized absorber and an upper limit on a distance of 2.5 pc for the lowest ionized absorber. The three ionization components lie on the stable branch of the thermal equilibrium curve, indicating roughly the same gas pressure. Therefore, the thermal wind from the torus is most likely the origin of warm absorbing gas in Mrk 290.

During the XMM-Newton observation, the ionizing luminosity was 50 per cent lower compared to that in the Chandra observation. The Reflection Grating Spectrometer spectrum is well fitted by a two-phase warm absorber, with several additional absorption lines attributed to a Galactic high-velocity cloud, complex C. Neither the ionization parameter ξ nor the column density N_H of the two absorbing components varied significantly, compared to the results from Chandra observations. The outflow velocities of both components were 1260 km/s. We suggest that an entirely new warm absorber from the torus passed through our line of sight.

Assuming the torus wind model, the estimated mass outflow rate is ∼ 0.1 M_☉ per year while the nuclear accretion rate is ∼ 0.04 M_☉ per year. The O VII and Ne IX forbidden lines are the most prominent soft X-ray emission lines, with a mean redshift of 700 km/s relative to the systematic velocity. There seems to be no relation between emission lines and warm absorbers.