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Register a new userEvidence for ionized reprocessing in the X-ray spectrum of the Seyfert 1 Galaxy 1E1615+061
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M.Guainazzi
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The Seyfert 1 galaxy 1E1615+061 was observed to display a very steep and intense soft X-ray spectrum during a HEAO-1 A2 observation in the 1978. Such an exceptionally soft X-ray state has never been observed subsequently, but the source has continued to exhibit a large (up to a factor 6) range of X-ray intensity variability. The overall UV/X-ray spectrum of this source, observed during a multiwavelength campaign in 1991-1992, can be well fit with a self-consistent, low-m-dot accretion disk model. In this model, the soft X-rays result were suggested to arise from reflection of the nuclear emission by mildly ionized material in the inner regions of the disk. In this Paper we report the results of an ASCA observation in 1995 August, which give a direct confirmation of such a scenario. The spectrum may be modeled as a power-law with a photon index of 1.8, together with absorption consistent with the galactic line of sight value, substantial reflection from ionized material and an iron fluorescent K-alpha emission line. The centroid energy (~6.6--6.8 keV) implies a ionization stage >Fe XIX. The line profile is consistent with that expected from a kinematically and gravitationally distorted line around a black hole. These results provide the first direct evidence for the existence of considerable amount of ionized material around the nucleus of a broad Seyfert 1 galaxy.
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Beginning in 1999 January, the bright, strongly variable Narrow-Line Seyfert 1 (NLS1) galaxy Akn 564 has been observed by RXTE once every ~4.3 days. It was also monitored every ~3.2 hr throughout 2000 July. These evenly-sampled observations have allowed the first quantitative comparison of long and short time-scale X-ray variability in an NLS1 and the derivation of an X-ray Power Density Spectrum (PDS). The variability amplitude in the short time-scale light curve is very similar to that in the long time-scale light curve, in marked contrast to the stronger variability on longer time-scales which is characteristic of normal broad-line Seyfert 1s (BLS1s). Furthermore, the Akn 564 PDS power law cuts off at a frequency of 8.7x10^-7 Hz corresponding to a timescale of ~13 d, significantly shorter than that seen in the PDS of NGC 3516, a BLS1 of comparable luminosity. This result is consistent with NLS1s showing faster (as opposed to larger amplitude) variations than BLS1s, providing further evidence that NLS1s harbour lower mass black holes than BLS1s of similar luminosity, accreting at a correspondingly higher relative rate.
There is growing evidence for the presence of blueshifted Fe K absorption lines in a number of radio-quiet AGNs and QSOs. These may be fundamental to probe flow dynamics near supermassive black holes. Here we aim at verifying and better characterising the existence of such Fe K absorption at ~8-10 keV in the luminous Seyfert 1 galaxy Mrk509, one of the most promising target for these studies. We present a comprehensive spectral analysis of the six XMM-Newton observations of the source (for a total of ~200 ks), focusing on the detailed and systematic search for absorption features in the high-energy data. We detect several absorption features at rest-frame energies ~8-8.5 keV and ~9.7 keV. The lines are consistent with being produced by H-like iron Ka and Kb shell absorptions associated with an outflow with mildly relativistic velocity of ~0.14-0.2 c. The lines are found to be variable in energy and, marginally in intensity, implying that variations in either the column density, geometry and/or ionization structure of the outflow are common in this source.
Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$alpha$ emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K$alpha$ line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall 9 and show that a face-on toroidal X-ray reprocessor model involving only nonrelativistic and mundane physics provides an excellent fit to the data. The Fe K$alpha$ line emission and Compton reflection continuum are calculated self-consistently, the iron abundance is solar, and an equatorial column density of $sim 10^{24} rm cm^{-2}$ is inferred. In this scenario, neither the Fe K$alpha$ line, nor the Compton-reflection continuum provide any information on the black-hole spin. Whereas previous analyses have assumed an infinite column density for the distant-matter reprocessor, the shape of the reflection spectrum from matter with a finite column density eliminates the need for a relativistically broadened Fe K$alpha$ line. We find a 90 per cent confidence range in the Fe K$alpha$ line FWHM of $1895$-$6205 rm km s^{-1}$, corresponding to a distance of $sim 3100$ to $33,380$ gravitational radii from the black hole, or $0.015$-$0.49$ pc for a black-hole mass of $sim 1-3 times 10^{8} M_{odot}$.
A model for the inner regions of accretion flows is presented where, due to disc instabilities, cold and dense material is clumped into deep sheets or rings. Surrounding these density enhancements is hot, tenuous gas where coronal dissipation processes occur. We expect this situation to be most relevant when the accretion rate is close to Eddington and the disc is radiation-pressure dominated, and so may apply to Narrow-Line Seyfert~1 (NLS1) galaxies. In this scenario, the hard X-ray source is obscured for most observers, and so the detected X-ray emission would be dominated by reflection off the walls of the sheets. A simple Comptonization calculation shows that the large photon-indices characteristic of NLS1s would be a natural outcome of two reprocessors closely surrounding the hard X-ray source. We test this model by fitting the XMM-Newton spectrum of the NLS1 1H 0707-495 between 0.5 and 11 keV with reflection dominated ionized disc models. A very good fit is found with three different reflectors each subject to the same Gamma=2.35 power-law. An iron overabundance is still required to fit the sharp drop in the spectrum at around 7 keV. We note that even a small corrugation of the accretion disc may result in Gamma > 2 and a strong reflection component in the observed spectrum. Therefore, this model may also explain the strength and the variability characteristics of the MCG-6-30-15 Fe K line. The idea needs to be tested with further broadband XMM-Newton observations of NLS1s.
We have characterized the energy-dependent X-ray variability properties of the Seyfert~1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-ray Timing Explorer data. The high-frequency fluctuation power spectral density function (PSD) slope is consistent with flattening towards higher energies. Light curve cross correlation functions yield no significant lags, but peak coefficients generally decrease as energy separation of the bands increases on both short and long timescales. We have measured the coherence between various X-ray bands over the temporal frequency range of 6e-8 to 1e-4 Hz; this range includes the temporal frequency of the low-frequency power spectral density function (PSD) break tentatively detected by Markowitz et al. and includes the lowest temporal frequency over which coherence has been measured in any AGN to date. Coherence is generally near unity at these temporal frequencies, though it decreases slightly as energy separation of the bands increases. Temporal frequency-dependent phase lags are detected on short time scales; phase lags are consistent with increasing as energy separation increases or as temporal frequency decreases. All of these results are similar to those obtained previously for several Seyfert galaxies and stellar-mass black hole systems. Qualitatively, these results are consistent with the variability models of Kotov et al. and Lyubarskii, wherein the X-ray variability is due to inwardly propagating variations in the local mass accretion rate.
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