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Register a new user1H0419-577: A two-state soft X-ray Seyfert galaxy
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M.Guainazzi
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In this paper we report on the first simultaneous optical and X-ray (Beppo-SAX) observations of the radio-quiet AGN 1H0419-577. The optical spectrum clearly leads us to classify this source as a Seyfert 1. The X-ray spectrum is, however, somewhat at odds with this classification: a simple flat (Gamma ~ 1.55) and featureless power--law is a good description of the whole 1.8-40 keV spectrum, even if the upper limit to a broad iron line is not very tight. An analysis of a still unpublished ROSAT observation of the same target reveals that the soft X-ray spectrum has undergone a transition from a steep (Gamma ~ 2.5) to a flat (Gamma ~ 1.55) state, at least in the 0.7-2 keV band. If this difference is due to a remarkably variable soft excess, it is unlikely that a single component is responsible for the optical/UV/soft X-ray spectral distribution. The hypothesis that the difference is due to a change in the primary X-ray continuum and its implications for current Comptonization models are discussed.
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The preliminary results of the BeppoSAX observation of the radio-quiet AGN 1H0419-577 are presented. Despite its broad line optical spectrum, the intermediate X-ray spectrum (i.e. 2--10 keV) is flatter than typically observed in Seyfert 1s and no iron line is significantly detected. Even more intriguingly, a 1992 ROSAT pointed observation suggests a dramatic (~ 1) change in the spectral shape for E < 2 keV. Such behavior is briefly discussed in the framework of our current understanding of Comptonization scenarios in the nuclear regions of radio-quiet AGN.
We report results obtained from six XMM-Newton observations of the Seyfert galaxy 1H 0419-577. Here we show that the X-ray spectrum and variability are well described by a two-component model comprising a power law with constant spectral shape and variable normalisation and a much more constant ionised reflection component from the inner accretion. One of the observations was performed when the source was in a particularly low flux state in which the X-ray spectrum is rather peculiar and exhibits a very flat hard spectrum with broad residuals below 6.6 keV and a steep soft excess below about 1 keV. We interpret the spectrum as being reflection-dominated by X-ray reprocessed emission from the inner accretion disc. The primary continuum is almost completely unobserved possibly because of strong light bending towards the central black hole. The ionised reflection model simultaneously accounts for the broad residuals and hard flat spectrum and for the soft excess. The same model provides an excellent description of the data at all the other flux levels, the most important difference being a variation in the power law normalisation. Our results imply that most of the X-ray emission in this source originates from within few gravitational radii from the central black hole and requires that the compact object is an almost maximally spinning Kerr black hole. (abridged)
In this paper we present the longest exposure (97 ks) XMM-Newton EPIC-pn spectrum ever obtained for the Seyfert 1.5 galaxy 1H 0419-577. With the aim of explaining the broadband emission of this source, we took advantage of the simultaneous coverage in the optical/UV that was provided in the present case by the XMM-Newton Optical Monitor and by a HST-COS observation. Archival FUSE flux measurements in the FUV were also used for the present analysis. We successfully modeled the X-ray spectrum together with the optical/UV fluxes data points using a Comptonization model. We found that a blackbody temperature of $T sim 56$ eV accounts for the optical/UV emission originating in the accretion disk. This temperature serves as input for the Comptonized components that model the X-ray continuum. Both a warm ($T_{rm wc} sim 0.7 $ keV, $tau_{rm wc} sim 7 $) and a hot corona ($T_{rm hc} sim 160 $ keV, $tau_{rm hc} sim 0.5$) intervene to upscatter the disk photons to X-ray wavelengths. With the addition of a partially covering ($C_vsim50%$) cold absorber with a variable opacity ($ {it N}_{rm H}sim [10^{19}- 10^{22}] ,rm cm^{-2}$), this model can well explain also the historical spectral variability of this source, with the present dataset presenting the lowest one (${it N}_{rm H}sim 10^{19} , rm cm^{-2} $). We discuss a scenario where the variable absorber, getting ionized in response to the variations of the X-ray continuum, becomes less opaque in the highest flux states. The lower limit for the absorber density derived in this scenario is typical for the broad line region clouds. Finally, we critically compare this scenario with all the different models (e.g. disk reflection) that have been used in the past to explain the variability of this source
We present detailed broadband UV/optical to X-ray spectral variability of the Seyfert 1 galaxy 1H 0419-577 using six XMM-Newton observations performed during 2002-2003. These observations covered a large amplitude variability event in which the soft X-ray (0.3-2 keV) count rate increased by a factor of ~4 in six months. The X-ray spectra during the variability are well described by a model consisting of a primary power law, blurred and distant reflection. The 2-10 keV power-law flux varied by a factor ~7 while the 0.3-2 keV soft X-ray excess flux derived from the blurred reflection component varied only by a factor of ~2. The variability event was also observed in the optical and UV bands but the variability amplitudes were only at the 6-10% level. The variations in the optical and UV bands appear to follow the variations in the X-ray band. During the rising phase, the optical bands appear to lag behind the UV band but during the declining phase, the optical bands appear to lead the UV band. Such behavior is not expected in the reprocessing models where the optical/UV emission is the result of reprocessing of X-ray emission in the accretion disc. The delayed contribution of the broad emission lines in the UV band or the changes in the accretion disc/corona geometry combined with X-ray reprocessing may give rise to the observed behavior of the variations.
In this paper we present a temporal and spectral analysis of X-ray data from the XMM and Chandra observations of the ultrasoft and variable Seyfert galaxy RX J1301.9+2747. In both observations the source clearly displays two distinct states in the X-ray band, a long quiescent state and a short flare (or eruptive) state which differs in count rates by a factor of 5--7. The transition from quiescent to flare state occurs in 1--2 ks. We have observed that the quiescent state spectrum is unprecedentedly steep with a photon index Gamma~7.1, and the spectrum of the flare state is flatter with Gamma~4.4. X-rays above 2 keV were not significantly detected in either state. In the quiescent state, the spectrum appears to be dominated by a black body component of temperature about ~30--40 eV, which is comparable to the expected maximum effective temperature from the inner accretion disk. The quiescent state however, requires an additional steep power-law, presumably arising from the Comptonization by transient heated electrons. Optical spectrum from the Sloan Digital Sky Survey shows Seyfert-like narrow lines for RX J1301.9+2747, while the HST imaging reveals a central point source for the object. In order to precisely determine the hard X-ray component, future longer X-ray observations are required. This will help constrain the accretion disk model for RX J1301.9+2747, and shed new light into the characteristics of the corona and accretion flows around black holes.
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