Abstract
(Abridged) We present a two month Suzaku X-ray monitoring of the Seyfert 1 galaxy NGC 5548. The campaign consists of 7 observations. We analyze the response in the opacity of the gas that forms the ionized absorber to ionizing flux variations. Despite variations by a factor of 4 in the impinging continuum, the soft X-ray spectra of the source show little spectral variations, suggesting no response from the ionized absorber. A detailed time modeling confirms the lack of opacity variations for an absorbing component with high ionization. Instead, the models tentatively suggest that the ionization parameter of a low ionization absorbing component might be changing with the ionizing flux, as expected for gas in photoionization equilibrium. Using the lack of variations, we set an upper limit of n_e <2.0E7 cm-3 for the electron density of the gas forming the high ionization, high velocity component. This implies a large distance from the continuum source (R > 0.033 pc). If the variations in the low ionization component are real, they imply n_e >9.8E4 cm-3 and R < 3 pc. We discuss our results in terms of two different scenarios: a large scale outflow originating in the inner parts of the accretion disk, or a thermally driven wind originating much farther out. Given the large distance of the wind, the implied mass outflow rate is also large (Mw > 0.08 Maccr). The associated total kinetic energy deployed by the wind in the host galaxy (>1.2E56 erg) can be enough to disrupt the interstellar medium, possibly regulating large scale star formation. The total mass and energy ejected by the wind is still lower than the one required for cosmic feedback, even when extrapolated to quasar luminosities. Such feedback would require that we are observing the wind before it is fully accelerated.
Highlights
The neutral, photoionized iron K emission line commonly found in the X-ray spectra of active galactic nuclei (AGNs) can be decomposed into a narrow core around 6.4 keV and a broad redshifted component, though sometimes only one of them is present (Fabian et al 2000; Yaqoob et al 2001; Nandra et al 1997, 2007)
A broad-line region (BLR) origin is supported by the quasi-simultaneous optical spectroscopic observation with Chandra observation of NGC 7213 (Bianchi et al 2008), which shows consistent Fe K and Hβ line widths, and by the rapid NH changes seen in several AGNs (Elvis et al 2004; Puccetti et al 2007; Risaliti et al 2002), which require a BLR-like radius for the NH 1023 cm−2 absorbers
Due to the weak reflection component in NGC 5548 (e.g., Pounds et al 2003), if we simultaneously fit the continua in the X-ray Imaging Spectrometer (XIS) and PIN spectra of each observation using the pexrav model instead of the power-law model, the intensity of the Fe K line will systematically decrease by 10% for each observation
Summary
The neutral, photoionized iron K emission line commonly found in the X-ray spectra of active galactic nuclei (AGNs) can be decomposed into a narrow core around 6.4 keV and a broad redshifted component, though sometimes only one of them is present (Fabian et al 2000; Yaqoob et al 2001; Nandra et al 1997, 2007). A BLR origin is supported by the quasi-simultaneous optical spectroscopic observation with Chandra observation of NGC 7213 (Bianchi et al 2008), which shows consistent Fe K and Hβ line widths, and by the rapid NH changes seen in several AGNs (Elvis et al 2004; Puccetti et al 2007; Risaliti et al 2002), which require a BLR-like radius for the NH 1023 cm−2 absorbers. Seen from another angle, these absorbers must reemit in Fe K.
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