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Context. The soft excess, a surplus of X-ray photons below 2 keV with respect to a power law, is a feature of debated physical origin found in the X-ray spectra of many type-1 active galactic nuclei (AGN). The eROSITA instrument aboard the Spectrum-Roentgen-Gamma (SRG) mission will provide an all-sky census of AGN. Spectral fitting of these sources can help identify the physical origin of the soft excess. Aims. The eROSITA Final Equatorial Depth Survey (eFEDS) field, designed to mimic the expected average equatorial depth of the all-sky survey, provides the ideal sample to test the power of eROSITA. The primary goal of this work is to test a variety of models for the soft X-ray emission of AGN (thermal emission, non-thermal emission, ionised absorption, or neutral partial covering absorption) to help identify the physical origin of the soft X-ray spectral complexity. Differences between these models are examined in the context of this sample to understand the physical properties. Methods. We used Bayesian X-ray analysis to fit a sample of 200 AGN from the eFEDS hard X-ray–selected sample with a variety of phenomenological and physically motivated models. Model selection is performed using the Bayes factor to compare the applicability of each model for individual sources as well as for the full sample, and source properties are compared and discussed. Black hole masses and Eddington ratios were estimated from optical spectroscopy. Results. We find that 29 sources have evidence for a soft excess at a confidence level > 97.5%, all of which are better modelled by an additional soft power-law, as opposed to thermal blackbody emission. Applying more physically motivated soft excess emission models, we find that 23 sources prefer a warm corona model, while only six sources are best fit with relativistic blurred reflection. Sources with a soft excess show a significantly higher Eddington ratio than the remainder of the sample. Of the remainder of the sample, many sources show evidence for complex absorption, with 29 preferring a warm absorber, and 25 a partial covering absorber. Many (18/26) sources that show significant neutral absorption when modelled with an absorbed power law, in fact show evidence that the absorber is ionised, which has important implications on the understanding of obscured AGN. In contrast to the soft excesses, warm absorber sources show significantly lower Eddington ratios than the remainder of the sample. We discuss the implications of these results for the physical processes in the central regions of AGN. Conclusions. Spectral fitting with Bayesian statistics is ideal for the identification of complex absorption and soft excesses in the X-ray spectra of AGN, and can allow one to distinguish between different physical interpretations. Applying the techniques from this work to the eROSITA all-sky survey will provide a more complete picture of the prevalence and origin of soft excesses and warm absorbers in type-1 AGN in the local Universe. [ABSTRACT FROM AUTHOR]

We selected sources with a steep soft-X-ray-band spectrum with a photon index of Γ > 2.5 – measured by eROSITA on board the Spectrum-Röntgen-Gamma (SRG) – from the eFEDS AGN catalogue as candidates of highly accreting supermassive black holes, and investigated their multi-wavelength properties. Among 601 bright AGN with 0.2−5 keV counts of greater than 100, 83 sources (≈14%) are classified as steep-spectrum sources. These sources have typical 0.5−2 keV luminosities of LSX ≈ 1044 erg s−1 and the majority of them are found at redshifts below z = 1. In comparison with sources with flatter spectra, these sources have, on average, a UV (or optical) to 2 keV luminosity ratio that is larger by ∼0.3 dex and bluer optical-to-UV continuum emission. They also appear to be radio quiet based on the detection rate in the FIRST and VLASS surveys. Their host galaxies – at least in the redshift range of z = 0.2 − 0.8, where the AGN–galaxy decomposition results from the Subaru Hyper Suprime-Cam imaging are available – tend to be late-type and have smaller stellar masses (M⋆ ∼ 1010.5 M⊙) than those of sources with flatter spectra. These properties are similar to those found in nearby narrow-line Seyfert 1 galaxies, in agreement with the picture that they are AGN with elevated accretion rates and are in the early growth phase of black hole and galaxy co-evolution. However, the steep-spectrum sources are not exclusively narrow-line Seyfert 1 galaxies; indeed many are broad-line Seyfert 1 galaxies, as found by a catalogue search. This suggests that these steep-spectrum sources may be black holes generally with high accretion rates but of a wide mass range, including a few objects emitting at LSX ≥ 1045 erg s−1, of which black hole masses can be close to 109 M⊙. [ABSTRACT FROM AUTHOR]

PHL 1092 is a z ∼ 0.4 high-luminosity counterpart of the class of Narrow–Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM–Newton observation. Its 2 keV flux density had dropped by a factor of ∼ 260 with respect to a previous observation performed 4.5 yr earlier. The UV flux remained almost constant, resulting in a significant steepening of the optical-to-X-ray slope αox from − 1.57 to − 2.51, making PHL 1092 one of the most extreme X-ray weak quasars with no observed broad absorption lines (BALs) in the UV. We have monitored the source since 2008 with three further XMM–Newton observations, producing a simultaneous UV and X-ray database spanning almost 10 yr in total in the activity of the source. We present here results from our monitoring campaign.

We present a resumé on the modified theory of gravity, called pseudo-complex General Relativity (pc-GR). It is the second in a series of papers, where the first one (Boller et al. 2019 ; referred to as Paper I) discussed the observational consequences of pc-GR. In this paper, we concentrate on the underlying theory. PC-GR involves an algebraic extension of the standard theory of GR and it depends on two phenomenological parameters. An element included in pc-GR that is not present in standard GR is the energy–momentum tensor corresponding to an anisotropic ideal fluid, which we call dark energy. The two parameters are related to the coupling of mass to the dark energy and its fall-off as a function of r. The consequences and predictions of this theory will be discussed in the context of the observational results of the Even Horizon Telescope, expected soon. Our main result is that due to the accumulation of dark energy near a large mass, the modified theory predicts a dark ring followed by a bright ring in the emission profile of the accretion disc. We also discuss the light ring in the equatorial plane. [ABSTRACT FROM AUTHOR]

A modified theory of gravity, avoiding singularities in the standard theory of gravitation, has been developed by Hess & Greiner, known as the pseudo-complex theory of gravitation. The pseudo-complex General Relativity (pc-GR) theory shows remarkable observational differences with respect to standard GR. The intensity profiles are significantly different between both theories, which is a rare phenomenon in astrophysics. This will allow robust tests of both theories using Event Horizon Telescope observations of the Galactic Centre. We also predict the time evolution of orbiting matter. In this paper we summarize the observational tests we have developed to date. The theory is described in the second paper of this series (referred to as paper II hereafter). [ABSTRACT FROM AUTHOR]

This work presents the catalogue of optical spectral properties for all X-ray selected SPIDERS active galactic nuclei (AGN) up to SDSS DR14. SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV programme that is currently conducting optical spectroscopy of the counterparts to the X-ray selected sources detected in the ROSAT all-sky survey and the XMM-Newton slew survey in the footprint of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The SPIDERS DR14 sample is the largest sample of X-ray selected AGN with optical spectroscopic follow-up to date. The catalogue presented here is based on a clean sample of 7344 2RXS (z¯ = 0.5 z ¯ = 0.5 $ \bar{z}=0.5 $) and 1157 XMM-Newton slew survey (z¯ = 0.4 z ¯ = 0.4 $ \bar{z}=0.4 $) type 1 AGN with spectroscopic coverage of the Hβ and/or MgII emission lines. Visual inspection results for each object in this sample are available from a combination of literature sources and the SPIDERS group, which provide both reliable redshifts and source classifications. The spectral regions around the Hβ and MgII emission lines have been fit in order to measure both line and continuum properties, estimate bolometric luminosities, and provide black hole mass estimates using the single-epoch (or photoionisation) method. The use of both Hβ and MgII allows black hole masses to be estimated up to z ≃ 2.5. A comparison is made between the spectral properties and black hole mass estimates derived from Hβ and MgII using the subsample of objects which have coverage of both lines in their spectrum. These results have been made publicly available as an SDSS-IV DR14 value added catalogue. [ABSTRACT FROM AUTHOR]

We have updated and improved the source catalog obtained from the ROSAT all-sky survey. In this new version of the source catalog (Second ROSAT all-sky survey, 2RXS), we have made a number of improvements, paying particular care to reduce spurious sources. The final catalog contains about 135,000 X-ray sources, thereby providing the deepest and cleanest all-sky survey to date. For each source, new data products, including spectra and light curves, were created, allowing to take full advantage of this catalog for new scientific explorations. [ABSTRACT FROM AUTHOR]

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is a Sloan Digital Sky Survey IV (SDSS-IV) survey running in parallel to the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected active galactic nuclei (AGN) and galaxy cluster members detected in wide-area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM-Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour- magnitude information from the Wide-field Infrared Survey Explorer survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright welllocalized X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ~12 000 ROSAT and ~1500 XMM-Newton Slew survey sources that have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS programme, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ~7500 deg2 for >85 per cent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17 < r < 22.5, producing a large and highly complete sample of bright X-ray-selected AGN suitable for statistical studies of AGN evolution and clustering. [ABSTRACT FROM AUTHOR]

ABSTRACT PHL 1092 is a z ∼ 0.4 high-luminosity counterpart of the class of Narrow-Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM-Newton observation. Its 2 keV flux density had dropped by a factor of ∼260 with respect to a previous observation performed 4.5 yr earlier. The ultraviolet (UV) flux remained almost constant, resulting in a significant steepening of the optical-to-X-ray slope αox from −1.57 to −2.51, making PHL 1092 one of the most extreme X-ray weak quasars with no observed broad absorption lines (BALs) in the UV. We have monitored the source since 2008 with three further XMM-Newton observations, producing a simultaneous UV and X-ray data base spanning almost 10 yr in total in the activity of the source. Our monitoring programme demonstrates that the αox variability in PHL 1092 is entirely driven by long-term X-ray flux changes. We apply a series of physically motivated models with the goal of explaining the UV-to-X-ray spectral energy distribution and the extreme X-ray and αox variability. We consider three possible models. (i) A breathing corona scenario in which the size of the X-ray-emitting corona is correlated with the X-ray flux. In this case, the lowest X-ray flux states of PHL 1092 are associated with an almost complete collapse of the X-ray corona down to the marginal stable orbit. (ii) An absorption scenario in which the X-ray flux variability is entirely due to intervening absorption. If so, PHL 1092 is a quasar with standard X-ray output for its optical luminosity, appearing as X-ray weak at times due to absorption. (iii) A disc-reflection-dominated scenario in which the X-ray-emitting corona is confined within a few gravitational radii from the black hole at all times. In this case, the intrinsic variability of PHL 1092 only needs to be a factor of ∼10 rather than the observed factor of ∼260. We discuss these scenarios in the context of non-BAL X-ray weak quasars. [ABSTRACT FROM AUTHOR]

A fragment of DNA (pBTBX) from the genome of Sinorhizobium fredii USDA257 was sequenced by shotgun strategy to identify the potential genes which enabled the Rhizobium species NGR234 to fix nitrogen on soybean, Glycine max (L.) Merr cv. Peking. The total length of the cosmid is 32,824 base pairs with a GC content of 61%. A 29 open reading frames (ORF) were identified representing 71.8% (23,574 bp) of the cosmid. Out of these ORF, 96.5% (22,749 bp) were identical and similar to reported and hypothetical genes and proteins. The remaining 3.5% (825 bp) had no apparent similarity to any genes in the data base. Gene and gene products found on the DNA fragment include those involved in the synthesis of FeMo component of nitrogenase, regulation of nitrogen fixation, transport of amino acids and sugars, chemotaxis and transcriptional regulation. [ABSTRACT FROM AUTHOR]

We present optical and X-ray data for a sample of serendipitous XMM–Newton sources that are selected to have 0.5–2 versus 2–4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2–4.5 keV X-ray flux , and in this paper we examine a subsample of 42 optically bright sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association rather than the correct identification of the X-ray source. The X-ray spectra of all the sources are consistent with heavily absorbed power laws , and all of them, including the two sources with 2–10 keV intrinsic luminosities of , appear to be absorbed active galactic nuclei (AGN). The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type 2 AGN. Three sources have 2–10 keV luminosities of , and two of these sources have optical spectra which are dominated by narrow emission lines, that is, are type 2 QSOs. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have . This implies that ratios of X-ray absorption to optical/ultraviolet extinction equivalent to times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few per cent of the population), and may be restricted to broad absorption line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law; all seven are narrow emission-line objects with and 2–10 keV intrinsic luminosities . We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that per cent of broad-line AGN (BLAGN) have ionized absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray-absorbed BLAGN in our sample the X-ray spectrum requires an ionized absorber, consistent with this picture. [ABSTRACT FROM AUTHOR]

We present a spectral analysis of the narrow-line Seyfert 1 galaxy I Zwicky 1, focusing on the characteristics of the ionized absorbers as observed with XMM–Newton in 2005. The soft X-ray spectrum shows absorption by two components of ionized gas with a similar column density and ionization parameters and 2.5. Comparing this observation with a 2002 XMM–Newton data set, we see a clear anticorrelation between the X-ray ionization parameter and the 0.1–10 keV luminosity. Viable explanations for this effect include transient clouds or filaments crossing the line of sight in a complex geometry or a gas observed in non-equilibrium. The outflow velocity of the X-ray low-ionization absorber is consistent with the outflow of the ultraviolet (UV) absorber detected in a past Hubble Space Telescope observation. In addition, the ionic column densities of C iv and N v derived from the X-ray model are consistent with the UV values. This suggests that the low-ionization outflowing gas may survive for many years, despite large changes in flux, and that there is a tight connection between the X-ray and UV absorbers that can only be confirmed with a simultaneous UV and X-ray observation. [ABSTRACT FROM AUTHOR]

An investigation of the spectral energy distribution (SED) of the compact steep-spectrum (CSS) source and possible radio-loud narrow-line Seyfert 1 galaxy (NLS1), PKS 2004–447, is presented. Five out of six well-studied radio-loud NLS1 share this dual classification [optically defined as an NLS1 with radio definition of a CSS or gigahertz-peaked spectrum (GPS) source], suggesting that the connection could have a physical origin. The SED is created from simultaneous observations (within 24 h) at radio (from Australia Telescope Compact Array), optical/near-infrared (NIR) (from Siding Spring) and UV/X-ray (from XMM–Newton) wavelengths. The X-ray data show evidence of short-term variability (primarily a ∼30 per cent increase in the final 4 ks of the observation), a possible soft excess and negligible absorption. Together with the rest of the SED, the X-ray emission is excessive in comparison to synchrotron plus synchrotron self-Compton (SSC) models. The SED can be described with a two-component model consisting of extended synchrotron/SSC emission with Comptonization in the X-rays, though SSC models with a very high electron-to-magnetic energy density ratio cannot be excluded either. The peak emission in the SED appears to be in the NIR, which can be attributed to thermal emission ( T≈ 1000 K) from a dusty torus. Analysis of a non-contemporaneous, low-resolution optical spectrum suggests that the narrow-line region (NLR) is much more reddened than the X-ray emitting region suggesting that the gas-to-dust ratio in PKS 2004–447 may be very different than in our own Galaxy. This could be achieved if the radio jets in PKS 2004–447 deposits material from the nucleus into the NLR. Long-term radio monitoring of PKS 2004–447 shows a rather constant light curve over nearly a six-month period with the exception of one outburst when the 6.65-GHz flux increased by ∼35 per cent over 19 d. It is not possible to differentiate between intrinsic or extrinsic (i.e. interstellar scintillation) origins for this outburst, but the detection of the rare event demonstrates the importance of intensive monitoring campaigns. In comparison to general samples of GPS sources, which appear to be X-ray weak, NLS1-CSS/GPS sources possess stronger X-ray emission relative to radio (comparable to normal radio-loud AGN). In addition, NLS1-CSS/GPS sources also exhibit lower intrinsic absorption than GPS sources of similar X-ray luminosity. This is consistent with the additional X-ray component required for PKS 2004–447, but larger samples of NLS1-CSS/GPS are needed before any conclusive remarks can be made. [ABSTRACT FROM AUTHOR]

We present a sample of 21 ROSAT bright active galactic nuclei (AGNs), representing a range of spectral classes, and selected for follow-up snapshot observations with XMM–Newton. The typical exposure was between 5 and 10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a ‘soft’sample. One of the main outcomes from the XMM–Newton observations was that all of the AGN, including 11 type 1.8–2 objects, required low levels of intrinsic absorption . The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the low-ionization nuclear emission regions (LINERs) NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at ∼ 5.8 keV. [ABSTRACT FROM AUTHOR]

Two short X-ray exposures (<3600 s each) of the radio-quiet Seyfert 1.2 galaxy UGC 3973 (Mrk 79) were conducted with XMM–Newton as part of an active galactic nucleus snapshot survey. In this paper we concentrate on the significance and possible origin of a narrow 8-keV (rest frame) line-like emission feature detected with the pn instrument during the second observation. Simulations show that the feature is significant at 96.0–98.4 per cent confidence, depending on what a priori assumptions are made. The feature cannot be attributed to background contamination and appears to be variable (or transient) because it was not detected in the first observation of UGC 3973 six months earlier. However, a constant feature cannot be completely dismissed, based on the 90 per cent upper limit on the flux from the first observation. There is some indication that the feature is variable over the duration of the second observation as well. We discuss various models (e.g. Ni emission, recombination edges, outflows, disc lines) which could potentially produce an emission feature at such energies. [ABSTRACT FROM AUTHOR]

We investigate the use of relativistically blurred photoionized disc models on an XMM–Newton observation of the narrow-line Seyfert 1 galaxy PG 1404+226. The model is designed to reproduce the radiation from the inner accretion disc around a Kerr black hole, and is more successful at fitting the spectrum than models based on a thermal soft excess. The source varies strongly over the course of the observation, and the disc model works over all observed flux states. We conclude that it is a useful tool in the study of certain quasars. [ABSTRACT FROM AUTHOR]

TheXMM–Newtonobservation of the narrow-line quasar NAB 0205+024 reveals three striking differences since it was last observed in X-rays withASCA. First, the 2–10 keV power law is notably steeper. Secondly, a hard X-ray flare is detected, very similar to that seen in I Zw 1. Thirdly, a strong and broad emission feature is detected with the bulk of its emission redward of 6.4 keV, and extending down to∼5 keV in the rest frame. The most likely explanation for the broad feature is neutral iron emission emitted from a narrow annulus of an accretion disc close to the black hole. The hard X-ray flare could be the mechanism that illuminates this region of the disc, allowing for the emission line to be detected. The combination of effects can be understood in terms of the‘thunder-cloud’ model proposed by Merloni&Fabian. [ABSTRACT FROM AUTHOR]

We apply a reflection-dominated model to the second XMM-Newton observation of the narrowline Seyfert 1 galaxy 1H 0707-495. As in the first XMM-Newton observation, a sharp spectral drop is detected with energy that has shifted from 7 to 7.5 kev in two years. The drop is interpreted in terms of relativistically blurred ionized reflection from the accretion disc, while the energy shift can be accounted for by changes in the ionization state and, more importantly, emissivity profile on the disc. A flatter emissivity profile during the second higher flux observation reduces gravitational redshift effects, therefore shifting the edge to higher energy. Remarkably, ionized disc reflection and the associated power-law continuum provide a reasonable description of the broad-band spectrum, including the soft excess. Considering both observations, the spectral variability in 1H 0707-495 appears to be a result of the interplay between these two spectral components. The reflection component in the second observation is significantly less variable than the power law. Changes of the emissivity profile, spectral shape and variability properties (such as the rms spectrum) within the two observations are all consistent with a recently proposed model in which relativistic effects in the very inner regions of the nucleus play a major role. [ABSTRACT FROM AUTHOR]

We compare two XMM-Newton observations of the narrow-line Seyfert 1 galaxy 1H0707-495, separated by two years, and discuss the results in terms of the partial-covering phenomenon. The second longer observation once again displays a sharp (<200 eV) spectral drop above 7 keV; however, in comparison with the first observation, the edge depth and energy have changed significantly. In addition to changes in the edge parameters, the high-energy spectrum appears steeper. The changes in the high-energy continuum can be adequately explained in terms of a partial-covering absorber outflowing from the central region. The low-energy spectrum also shows significant long-term spectral variability, including a substantial increase in the disc temperature, detection of a ∼0.9-keV emission feature and the presence of warm absorption that was also detected during the ASCA mission, but not seen during the first XMM-Newton observation. The large increase in disc temperature, and more modest rise in luminosity, can be understood if we consider the slim-disc model for 1H 0707-495. In addition, the higher disc luminosity could be the driving force behind the outflow scenario and the reappearance of a warm medium during the second XMM-Newton observation. [ABSTRACT FROM AUTHOR]

We report on two XMM–Newton observations of the bright narrow-line Seyfert 1 galaxy Ark 564 taken 1 yr apart (2000 June and 2001 June). The 0.6–10 keV continuum is well described by a soft blackbody component plus a steep power law . No significant spectral changes are observed between the two observations, although the X-ray flux in the second observation is ≈40–50 per cent lower. In both observations, we detect a significant absorption edge at a rest-frame energy of ≈0.73 keV, corresponding to O vii. The presence of the absorption feature is confirmed by a simultaneous Chandra grating observation in 2000 June, although the best-fitting edge threshold is at a slightly lower energy in the Chandra data, possibly because of a different parametrization of the underlying X-ray continuum. We find tentative evidence for a broad iron emission line in the 2000 June observation. The results from an analysis of the power spectral density (PSD) function are also presented. The present XMM–Newton data support the idea that the PSD shows two breaks, although the location of the high-frequency break requires further constraints. [ABSTRACT FROM AUTHOR]

We report on the XMM–Newton timing properties of the most X-ray variable, radio-quiet, narrow-line type 1 Seyfert galaxy IRAS 13224–3809. IRAS 13224–3809 continues to display the extremely variable behaviour that was previously observed with ROSAT and ASCA; however, no giant, rapid flaring events are observed. We detect variations by a factor as high as ∼8 during the 64-ks observation and the variability is persistent throughout the light curve. Dividing the light curve into 9-min segments, we found almost all of the segments to be variable at >3σ. When the time-averaged cross-correlation function is calculated for the 0.3–0.8 keV band with the 3–10 keV band, the cross-correlation profile is skewed, indicating a possible smearing of the signal to longer times (the soft band leading the hard). A correlation between count rate and hardness ratio is detected in four energy bands. In three cases, the correlation is consistent with spectral hardening at lower count rates, which can be explained in terms of a partial-covering model. The other band displays the reverse effect, showing spectral hardening at higher count rates. We can explain this trend as a more variable power-law component compared with the soft component. We also detect a delay between the 0.3–1.5 keV count rate and the 0.8–1.5 to 0.3–0.8 keV hardness ratio, implying flux-induced spectral variability. Such delays and asymmetries in the cross-correlation functions could suggest reprocessing of soft and hard photons. In general, much of the timing behaviour can be attributed to erratic eclipsing behaviour associated with the partial covering phenomenon, in addition to intrinsic variability in the source. The variability behaviour of IRAS 13224–3809 suggests a complicated combination of effects which we have started to disentangle with this present analysis. [ABSTRACT FROM AUTHOR]

We present an XMM-Newton observation of the bright, narrow-line, ultrasoft type 1 Seyfert galaxy Ton S180. The 0.3-10 keV X-ray spectrum is steep and curved, showing a steep slope above 2.5 keV (Γ ∼ 2.3) and a smooth, featureless excess of emission at lower energies. The spectrum can be adequately parametrized using a simple double power-law model. The source is strongly variable over the course of the observation but shows only weak spectral variability, with the fractional variability amplitude remaining approximately constant over more than a decade in energy. The curved continuum shape and weak spectral variability are discussed in terms of various physical models for the soft X-ray excess emission, including reflection off the surface of an ionized accretion disc, inverse Compton scattering of soft disc photons by thermal electrons, and Comptonization by electrons with a hybrid thermal/non-thermal distribution. We emphasize the possibility that the strong soft excess may be produced by dissipation of accretion energy in the hot, upper atmosphere of the putative accretion disc. [ABSTRACT FROM AUTHOR]