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Register a new userThe origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?
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L. C. Gallo
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In some radio-quiet active galaxies (AGN), high-energy absorption features in the x-ray spectra have been interpreted as Ultrafast Outflows (UFOs) -- highly ionised material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic velocities. In some cases, these outflows can carry energy in excess of the binding energy of the host galaxy. Needless to say, these features demand our attention as they are strong signatures of AGN feedback and will influence galaxy evolution. For the same reason, alternative models need to be discussed and refuted or confirmed. Gallo & Fabian proposed that some of these features could arise from resonance absorption of the reflected spectrum in a layer of ionised material located above and corotating with the accretion disc. Therefore, the absorbing medium would be subjected to similar blurring effects as seen in the disc. A priori, the existence of such plasma above the disc is as plausible as a fast wind. In this work, we highlight the ambiguity by demonstrating that the absorption model can describe the ~7.6 keV absorption feature (and possibly other features) in the quasar PG 1211+143, an AGN that is often described as a classic example of an UFO. In this model, the 2-10 keV spectrum would be largely reflection dominated (as opposed to power law dominated in the wind models) and the resonance absorption would be originating in a layer between about 6 and 60 gravitational radii. The studies of such features constitutes a cornerstone for future X-ray observatories like Astro-H and Athena+. Should our model prove correct, or at least important in some cases, then absorption will provide another diagnostic tool with which to probe the inner accretion flow with future missions.
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We investigate the X-ray time lags of a recent ~630ks XMM-Newton observation of PG 1211+143. We find well-correlated variations across the XMM-Newton EPIC bandpass, with the first detection of a hard lag in this source with a mean time delay of up to ~3ks at the lowest frequencies. We find that the energy-dependence of the low-frequency hard lag scales approximately linearly with log(E) when averaged over all orbits, consistent with the propagating fluctuations model. However, we find that the low-frequency lag behaviour becomes more complex on timescales longer than a single orbit, suggestive of additional modes of variability. We also detect a high-frequency soft lag at ~10^{-4}Hz with the magnitude of the delay peaking at <0.8ks, consistent with previous observations, which we discuss in terms of small-scale reverberation.
The analysis of a series of seven observations of the nearby ($z=0.0809$) QSO, PG 1211+143, taken with the Reflection Grating Spectrometer (RGS) on-board XMM-Newton in 2014, are presented. The high resolution soft X-ray spectrum, with a total exposure exceeding 600 ks, shows a series of blue-shifted absorption lines, from the He and H-like transitions of N, O and Ne, as well as from L-shell Fe. The strongest absorption lines are all systematically blue-shifted by $-0.06c$, originating in two absorption zones, from low and high ionization gas. Both zones are variable on timescales of days, with the variations in absorber opacity effectively explained by either column density changes or by the absorber ionization responding directly to the continuum flux. We find that the soft X-ray absorbers probably exist in a two-phase wind, at a radial distance of $10^{17}-10^{18}$ cm from the black hole, with the lower ionization gas as denser clumps embedded within a higher ionization outflow. The overall mass outflow rate of the soft X-ray wind may be as high as $2{rm M}_{odot}$ yr$^{-1}$, close to the Eddington rate for PG 1211+143 and similar to that previously deduced from the Fe K absorption.
An extended XMM-Newton observation of the luminous narrow line Seyfert galaxy PG 1211+143 in 2014 has revealed a more complex high velocity wind, with components distinguished in velocity, ionization level, and column density. Here we report soft x-ray emission and absorption features from the ionized outflow, finding counterparts of both high velocity components, v ~ 0.129c and v ~ 0.066c, recently identified in the highly ionized Fe K absorption spectrum. The lower ionization of the co-moving soft x-ray absorbers imply a distribution of higher density clouds embedded in the main outflow, while much higher column densities for the same flow component in the hard x-ray spectra suggest differing sight lines to the continuum x-ray source.
We present the results from a monitoring campaign of the Narrow-Line Seyfert~1 galaxy PG 1211+143. The object was monitored with ground-based facilities (UBVRI photometry; from February to July, 2007) and with Swift (X-ray photometry/spectroscopy and UV/Optical photometry; between March and May, 2007). We found PG 1211+143 in a historical low X-ray flux state at the beginning of the Swift monitoring campaign in March 2007. It is seen from the light curves that while violently variable in X-rays, the quasar shows little variations in optical/UV bands. The X-ray spectrum in the low state is similar to other Narrow-Line Seyfert 1 galaxies during their low-states and can be explained by a strong partial covering absorber or by X-ray reflection onto the disk. With the current data set, however, it is not possible to distinguish between both scenarios. The interband cross-correlation functions indicate a possible reprocessing of the X-rays into the longer wavelengths, consistent with the idea of a thin accretion disk, powering the quasar. The time lags between the X-ray and the optical/UV light curves, ranging from ~2 to ~18 days for the different wavebands, scale approximately as ~lambda^(4/3), but appear to be somewhat larger than expected for this object, taking into account its accretion disk parameters. Possible implications for the location of the X-ray irradiating source are discussed.
We present a detailed X-ray spectral study of the quasar PG 1211+143 based on Chandra High Energy Transmission Grating Spectrometer (HETGS) observations collected in a multi-wavelength campaign with UV data using the Hubble Space Telescope Cosmic Origins Spectrograph (HST-COS) and radio bands using the Jansky Very Large Array (VLA). We constructed a multi-wavelength ionizing spectral energy distribution using these observations and archival infrared data to create XSTAR photoionization models specific to the PG 1211+143 flux behavior during the epoch of our observations. Our analysis of the Chandra-HETGS spectra yields complex absorption lines from H-like and He-like ions of Ne, Mg and Si which confirm the presence of an ultra-fast outflow (UFO) with a velocity ~ $-$17,300 km s$^{-1}$ (outflow redshift $z_{rm out}$ ~ $-$0.0561) in the rest frame of PG 1211+143. This absorber is well described by an ionization parameter $log xi$ ~ 2.9 erg s$^{-1}$ cm and column density $log N_{rm H}$ ~ 21.5 cm$^{-2}$. This corresponds to a stable region of the absorbers thermal stability curve, and furthermore its implied neutral hydrogen column is broadly consistent with a broad Ly$alpha$ absorption line at a mean outflow velocity of ~ $-$16,980 km s$^{-1}$ detected by our HST-COS observations. Our findings represent the first simultaneous detection of a UFO in both X-ray and UV observations. Our VLA observations provide evidence for an active jet in PG 1211+143, which may be connected to the X-ray and UV outflows; this possibility can be evaluated using very-long-baseline interferometric (VLBI) observations.
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