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تسجيل مستخدم جديدThe warm absorber in NGC 5548: The lean years
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We study the variability of the warm absorber and the gas responsible for the emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the location and physical properties of these components. Using X-ray spectra taken with the textit{Chandra}$-$LETGS in 2002 and 2005, we study variability in the ionic column densities and line intensities. We find a lower ion{O}{vii} forbidden emission line flux in 2005, while the Fe K$alpha$ line flux stays constant. The warm absorber is less ionized in 2005, allowing us to constrain its location to within 7 pc of the central source. Using both the observed variability and the limit on the FWHM of the ion{O}{vii} f line, we have constrained the location of the narrow line region to a distance of 1 pc from the central source. The apparent lack of variability of the Fe K$ alpha$ line flux does not allow for a unique explanation.
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(Abridged) The archetypal Seyfert 1 galaxy NGC 5548 was observed in 2013-2014 in the context of an extensive multiwavelength campaign, which revealed the source to be in an extraordinary state of persistent heavy obscuration. We re-analyzed the archi
val grating spectra obtained by XMM-Newton and Chandra between 1999 and 2007 in order to characterize the classic warm absorber (WA) using consistent models and up-to-date photoionization codes and atomic physics databases and to construct a baseline model that can be used as a template for the WA in the 2013 observations. The WA in NGC 5548 is composed of 6 distinct ionization phases outflowing in 4 kinematic regimes in the form of a stratified wind with several layers intersected by our line of sight. If the changes in the WA are solely due to ionization or recombination processes in response to variations in the ionizing flux among the different observations, we are able to estimate lower limits on the density of the WA, finding that the farthest components are less dense and have a lower ionization. These limits are used to put stringent upper limits on the distance of the WA components from the central ionizing source, with the lowest ionization phases <50, <20, and <5 pc, respectively, while the intermediately ionized components lie at <3.6 and <2.2 pc from the center, respectively. The highest ionization component is located at ~0.6 pc or closer to the AGN central engine. The mass outflow rate summed over all WA components is ~0.3 Msun/yr, about six times the nominal accretion rate of the source. The total kinetic luminosity injected into the ISM is a small fraction (~0.03%) of the bolometric luminosity of the source. After adding the contribution of the UV absorbers, this value augments to ~0.2% of the bolometric luminosity, well below the minimum amount of energy required by current feedback models to regulate galaxy evolution.
We present the results from our 140 ks XMM-Newton and 500 ks Chandra observation of NGC 5548. The velocity structure of the X-ray absorber is consistent with the velocity structure measured in the simultaneous UV spectra. In the X-rays we can separat
e the highest outflow velocity component, -1040 km/s, from the other velocity components. This velocity component spans at least three orders of magnitude in ionization parameter, producing both highly ionized X-ray absorption lines (Mg XII, Si XIV) and UV absorption lines. A similar conclusion is very probable for the other four velocity components. We show that the lower ionized absorbers are not in pressure equilibrium with the rest of the absorbers. Instead, a model with a continuous distribution of column density versus ionization parameter gives an excellent fit to our data.
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e low energy absorbing column is significantly less than previously seen. Prominent O~vii and O~viii absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe~K$alpha$ emission line from cold material is present as well as a broad Fe~K$alpha$ line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low energy absorption. In addition to a highly ionized absorber with ionization parameter $U = 1.66$ and a total column density of $1.4 times 10^{22}~rm cm^{-2}$, adding a lower ionization absorber with $U = 0.32$ and a total column of $6.9 times 10^{21}~rm cm^{-2}$ significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to $< 160~rm km~s^{-1}$ at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.
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NGC 5548 was observed by BeppoSAX in a single long (8 day) observation from 0.2 to 200 keV. We find (1) the spectral variation of the source is produced by a change of the intrinsic power law slope; (2) a high energy cut-off at $E_c= 115^{+39}_{-27}$
keV with a hint of change of $E_c$ with flux; (3) OVII and OVIII absorption K edges, and a possible blended OVII-OVIII K$alpha,beta$ emission feature at $0.54^{+0.07}_{-0.06}$ keV, inconsistent with a purely photoionized gas in equilibrium. We propose that the temperature of the absorbing and emitting gas is $sim 10^6$ K so that both collisional ionization and photoionization contribute.
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