Warm absorber and truncated accretion disc in IRAS 05078+1626

Aims. We present a method that allows us to estimate the distance from the continuum source located in the center of AGN to the highly ionized gas called warm absorber. Methods. We computed a set of constant total pressure photoionization models compatible with the warm absorber conditions, where a metal-rich gas is irradiated by a continuum in the form of a double power law. The first power law is hard up to 100 keV and represents radiation from an X-ray source, while the second power law extends up to several eVs and illustrates radiation from an accretion disk. Results. When the ionized continuum is dominated by the soft component, the warm absorber is heated by free-free absorption, instead of Comptonization, and the transmitted spectra show different absorption line characteristics for different values of the hydrogen number density at the cloud illuminated surface. Conclusions. This fact results in the possibility of deriving the number density on the cloud illuminated side from observations and hence the distance to the warm absorber.

The recent observations of a highly ionized, X-ray absorbing gas in active galactic nuclei (AGN) suggest a new nuclear component, the so-called ‘warm absorber’. This gas is likely to be at a temperature of ~ 1–2 × 105 K and is most easily detected in the 0.5–10keV range, where several oxygen absorption edges are often observed.This review describes the properties of warm absorbers and the relation to other nuclear components, such as the broad-line emitting gas. The stability of the gas is a key issue and analysis shows that it is likely to be thermally stable, at the above mentioned temperature. When successful models are compared to the data, they can be used to infer the column density, composition and level of ionization of the X-ray absorbing gas. They also show that, on top of the strong continuum absorption, the gas must emit X-ray lines that are at the limit of detection by present day X-ray instruments.New calculations of X-ray emission lines emitted by ionized X-ray absorbers are shown and discussed. Various line equivalent widths are defined and examples are shown over a large range of column density and ionization parameter. The equivalent width of the strongest 0.5-5 keV lines is only a few tens of eV, but in cases of obscured X-ray source, like in Seyfert 2s, the lines are measured against the scattered and diffuse radiation with much larger equivalent widths. The X-ray absorbing and emitting gas is responsible also for a fraction of the observed flux of some UV emission lines. It is also the cause of the detection of several UV absorption lines. The calculations predict that some of those absorption lines, in particular 0 VI λ1035, are very sensitive warm-absorber tracers. Thus, analysis of the combined X-ray and UV properties is the best way to identify the location and properties of this gas.Understanding the origin and properties of warm X-ray absorbers is a major challenge of AGN research. Several new ideas are briefly discussed, trying to relate the location, mass, and motion of this gas to what is known about other observed nuclear components.

Results from the X-ray spectral analysis of the ASCA PV phase observation of the Seyfert 1 galaxy IC 4329A are presented. We find that the 0.4 - 10 keV spectrum of IC 4329A is best described by the sum of a steep ($\Gamma \sim 1.98$) power-law spectrum passing through a warm absorber plus a strong reflection component and associated Fe K line, confirming recent results (Madejski et al. 1995, Mushotsky et al. 1995). Further cold absorption in excess of the Galactic value and covering the entire source is also required by the data, consistent with the edge-on galactic disk and previous X-ray measurements. The effect of the warm absorber at soft X-ray energies is best parameterized by two absorption edges, one consistent with OVI, OVII or NVII, the other consistent with OVIII. A description of the soft excess in terms of blackbody emission, as observed in some other Seyfert 1 galaxies, is ruled out by the data. A large amount of reflection is detected in both the GIS and SIS detectors, at similar intensities. We find a strong correlation between the amount of reflection and the photon index, but argue that the best solution with the present data is that given by the best statistical fit. The model dependence of the Fe K line parameters is also discussed. Our best fit gives a slightly broad ($\sigma \simeq 0.11 \pm 0.08$ keV) and redshifted (E $\simeq 6.20 \pm 0.07$ keV) Fe K line, with equivalent width $\simeq$ 89 $\pm$ 33 eV. The presence of a weak Fe K line with a strong reflection can be reconciled if one assumes iron underabundances or ionized reflection. We also have modeled the line with a theoretical line profile produced by an accretion disk. This yields results in better agreement with the constraints obtained from the reflection component.

X-ray study of accretion flow in narrow-line Seyfert 1 galaxies

We present a detailed spectral analysis of XMM-Newton and NuSTAR observations of the accreting transient black hole GRS 1739−278 during a very faint low hard state at ∼0.02% of the Eddington luminosity (for a distance of 8.5 kpc and a mass of 10 ). The broadband X-ray spectrum between 0.5 and 60 keV can be well-described by a power-law continuum with an exponential cutoff. The continuum is unusually hard for such a low luminosity, with a photon index of Γ = 1.39 ± 0.04. We find evidence for an additional reflection component from an optically thick accretion disk at the 98% likelihood level. The reflection fraction is low, with . In combination with measurements of the spin and inclination parameters made with NuSTAR during a brighter hard state by Miller et al., we seek to constrain the accretion disk geometry. Depending on the assumed emissivity profile of the accretion disk, we find a truncation radius of 15–35 (5–12 ) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.

We observed Circinus X-1 twice during a newly reached low-flux phase near zero orbital phase using the High-Energy Transmission Grating Spectrometer (HETGS) onboard Chandra. In both observations the source did not show the P Cygni lines we observed during the high-flux phases of the source in 2000 and 2001. During pre-zero phase the source did not exhibit significant variability and exhibited an emission-line spectrum rich in H- and He-like lines from high Z elements such as Si, S, Ar, and Ca. We analyzed all high resolution X-ray spectra by fitting photoionization and absorption models from the most recent version of the XSTAR code. The pre-zero phase spectrum could be fully modeled with a very hot photoionized plasma with an ionization parameter of log xi = 3.0. Post-zero phase episodes feature absorbers with variable high columns, ionization parameter, and luminosity. While cold absorption remains at levels quite similar to the one observed in previous years, the new observations show unprecedented levels of variable warm absorption. The line emissivities also indicate that the observed low source luminosity is inconsistent with a static hot accretion disk corona (ADC), an effect that seems common to other near edge-on ADC sources as well. We conclude that unless there exists some means of coronal heating other than X-rays, the true source luminosity is likely much higher and we observe obscuration in analogy to the extragalactic Seyfert II sources. We discuss possible consequences and relate cold, luke-warm, warm, and hot absorbers to dynamic accretion scenarios.

Large flux change due to the intervening cold absorbers in NGC 3516

We report on the first observation of a radio-quiet active galactic nucleus (AGN) in polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source was pointed at with the Imaging X-ray Polarimetry Explorer (IXPE) starting on 2022 May 14 for a net observing time of 486 ks, simultaneously with XMM-Newton (58 ks) and NuSTAR (83 ks). A polarization degree Π smaller than 4.7 per cent (at the 99 per cent confidence level) is derived in the 2–8 keV energy range, where emission is dominated by the primary component ascribed to the hot corona. The broad-band spectrum, inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is well reproduced by a power law with photon index Γ = 1.85 ± 0.01 and a high-energy cutoff EC = 120 ± 15 keV. A comparison with Monte Carlo simulations shows that a lamp-post and a conical geometry of the corona are consistent with the observed upper limit, a slab geometry is allowed only if the inclination angle of the system is less than 50°.

We present a long (100 ks) Suzaku observation of one of the X-ray brightest AGN, MCG+8-11-11. These data were complemented with the 54-month Swift BAT spectrum, allowing us to perform a broad-band fit in the 0.6-150 keV range. The fits performed in the 0.6-10 keV band give consistent results with respect to a previous XMM-Newton observation, i.e. the lack of a soft excess, warm absorption along the line of sight, a large Compton reflection component (R~1) and the absence of a relativistic component of the neutral iron K$\alpha$ emission line. However, when the PIN and Swift BAT data are included, the reflection amount drops significantly (R~0.2-0.3), and a relativistic iron line is required, the latter confirmed by a phenomenological analysis in a restricted energy band (3-10 keV). When a self-consistent model is applied to the whole broadband data, the observed reflection component appears to be all associated to the relativistic component of the iron K$\alpha$ line. The resulting scenario, though strongly model-dependent, requires that all the reprocessing spectral components from Compton-thick material must be associated to the accretion disc, and no evidence for the classical pc-scale torus is found. The narrow core of the neutral iron K$\alpha$ line is therefore produced in a Compton-thin material, like the BLR, similarly to what found in another Seyfert galaxy, NGC7213, but with the notable difference that MCG+8-11-11 presents spectral signatures from an accretion disc. The very low accretion rate of NGC7213 could explain the lack of relativistic signatures in its spectrum, but the absence of the torus in both sources is more difficult to explain, since their luminosities are comparable, and their accretion rates are completely different.

The radiation from the central regions of active galactic nuclei, including that from the accretion disk surrounding the black hole, is likely to peak in the extreme ultraviolet $\sim 13 -100$ eV. However, due to Galactic absorption, we are limited to constrain the physical properties, i.e. the black hole mass and the accretion rate, from what observations we have below $\sim 10$ eV or above $\sim 100$ eV. In this paper we predict the thermal and ionization states of warm absorbers as a function of the shape of the unobservable continuum. In particular we model an accretion disk at $kT_{in} \sim 10$ eV and a {\it soft excess} at $kT_{se} \sim 150$ eV. The warm absorber, which is the highly ionized gas along the line of sight to the continuum, shows signatures in the $\sim 0.3 - 2$ keV energy range consisting of numerous absorption lines and edges of various ions, some of the prominent ones being H- and He-like oxygen, neon, magnesium and silicon. We find that the properties of the warm absorber are significantly influenced by the changes in the temperature of the accretion disk, as well as by the strength of the {\it soft excess}, as they affect the optical depth particularly for iron and oxygen. These trends may help develop a method of characterising the shape of the unobservable continuum and the occurrence of warm absorbers.

We present results obtained from three BeppoSAX observations of the accretion-powered transient X-ray pulsar KS 1947+300 carried out during the declining phase of its 2000 November -- 2001 June outburst. A detailed spectral study of KS 1947+300 across a wide X-ray band (0.1--100.0 keV) is attempted for the first time here. Timing analysis of the data clearly shows a 18.7 s pulsation in the X-ray light curves in the above energy band. The pulse profile of KS 1947+300 is characterized by a broad peak with sharp rise followed by a narrow dip. The dip in the pulse profile shows a very strong energy dependence. Broad-band pulse-phase-averaged spectroscopy obtained with three of the BeppoSAX instruments shows that the energy spectrum in the 0.1--100 keV energy band has three components, a Comptonized component, a ~0.6 keV blackbody component, and a narrow and weak iron emission line at 6.7 keV with a low column density of material in the line of sight. We place an upper limit on the equivalent width of the iron K_\alpha line at 6.4 keV of ~13 eV (for a width of 100 eV). Assuming a spherical blackbody emitting region and the distance of the source to be 10 kpc, the radius of the emitting region is found to be in the range of 14--22 km, which rules out the inner accretion disk as the soft X-ray emitting region.

We present the results of two Chandra observations (separated by 1 yr) of the population of X-ray sources in the spiral galaxy M51 (NGC 5194 and NGC 5195). One hundred and thirteen X-ray sources have been detected in an 84 × 84 (20.4 × 20.4 kpc) region, and 84 and 12 of them project within the disks of NGC 5194 and NGC 5195, respectively. Nine and 28 sources have luminosities exceeding 1 × 1039 ergs s-1 (ultraluminous X-ray sources or ULXs) and 1 × 1038 ergs s-1 in the 0.5-8 keV band, respectively, assuming that they are associated with M51. The number of ULXs is much higher than found in most normal spiral and elliptical galaxies. Most of the X-ray sources and all seven of the ULXs in NGC 5194 are located in, or close to, a spiral arm, suggesting a connection with recent star formation. The cumulative luminosity function of the X-ray sources in NGC 5194 with L(0.5-8 keV) > 1038 ergs s-1 is well described by a power law, N[>L(0.5-8 keV)] ∝ L(0.5- 8 keV)-α with α = 0.91. The X-ray spectra of most of the detected sources are consistent with a power law with a photon index between 1 and 2, with a few sources showing harder or softer spectra. The spectra of most ULXs are consistent with both a power law and a multicolor disk blackbody (MCD) model, while a power-law model is preferable to an MCD model in two ULXs. One ULX (NGC 5194 source 69) shows drastic spectral steepening accompanied by a decline in luminosity by a factor of 3460 in the 2-10 keV band between the two observations. This source also exhibited a possible period of 2.1 hr in the 2000 observation. Another ULX (NGC 5194 source 26) shows strong emission lines from highly ionized species. The masses of the compact objects and mass accretion rates in ULXs and other X-ray sources are not well constrained by these observations. If we adopt an MCD interpretation, their MCD parameters imply that most of the X-ray sources are stellar mass (~5-10 M☉) black holes accreting near or above the Eddington rate, although other possibilities (intermediate-mass black holes and relativistically beamed emission) cannot be excluded. The power-law sources may instead represent Comptonized disk or nonthermal emission. Two ULXs have very soft spectra; MCD models require kT ≈ 0.1 keV. We discuss the possibility that this soft emission originates in an accretion disk around an intermediate-mass black hole. We also present a study of the nucleus of, and discrete sources (including two ULXs) in, the companion galaxy NGC 5195.

We investigate accretion disc models for the X-ray emission of type 1 Seyfert galaxies and the hard state of black hole binaries. We concentrate on two hot accretion disc models: advectiondominated accretion flow (ADAF) and the recently found luminous hot accretion flow (LHAF). We solve for the global solution of both ADAF and LHAF to obtain the electron temperature, T e, and Thomson optical depth, τ ,a tthe radius where most of the radiation comes from. We adopt two kinds of electron energy equations. In one, only synchrotron and bremsstrahlung radiation and their Comptonization are considered. The other is parametrized by a constant Compton parameter to model the case in which thermal Comptonization of external soft photons is important. We compare the calculated T e and τ with the observational values obtained by fitting the average spectra of type 1 Seyfert galaxies and black hole binaries using the thermalComptonization model. We find that the most favoured model is an LHAF with a parametrized electron energy equation, with ADAFs predicting a too-high T e. Also, LHAF, but not ADAF, can explain the large luminosities in excess of 10 per cent of the Eddington luminosity seen in the hard state of transient black hole binaries. Ke yw ords: accretion, accretion discs ‐ black hole physics ‐ hydrodynamics ‐ radiation mechanisms: thermal ‐ galaxies: active ‐ galaxies: nuclei.

We investigated, using spectral-timing analysis, the characterization of highly ionized outflows in Seyfert galaxies, the so-called warm absorbers. Here, we present our results on the extensive ~ 600 ks of XMM-Newton archival observations of the bright and highly variable Seyfert 1 galaxy NGC 4051, whose spectrum has revealed a complex multicomponent wind. Making use of both RGS and EPIC-pn data, we performed a detailed analysis through a time-dependent photoionization code in combination with spectral and Fourier spectral-timing techniques. The source light curves and the warm absorber parameters obtained from the data were used to simulate the response of the gas due to variations in the ionizing flux of the central source. The resulting time variable spectra were employed to predict the effects of the warm absorber on the time lags and coherence of the energy dependent light curves. We have found that, in the absence of any other lag mechanisms, a warm absorber with the characteristics of the one observed in NGC 4051, is able to produce soft lags, up to 100 s, on timescales of ~ hours. The time delay is associated with the response of the gas to changes in the ionizing source, either by photoionization or radiative recombination, which is dependent on its density. The range of radial distances that, under our assumptions, yield longer time delays are comparable to the existing estimates of the location of the warm absorber in NGC 4051. For this reason, we suggest that it is likely that the observed X-ray time lags may carry a signature of the warm absorber response time, to changes in the ionizing continuum. These results highlight the importance of understanding the contribution of the warm absorber to the AGN X-ray time lags, since it is also vital information for interpreting the lags associated with propagation and reverberation effects in the inner emitting regions.

Context. PG 1535+547 is a bright Narrow Line Seyfert 1 galaxy, whose high-energy emission shows strong variability both in shape and flux. On the basis of ROSAT observations, it is classified as “soft X-ray weak quasi-stellar object (QSO)”, a class of objects whose X-ray-to-optical flux ratio is smaller than in typical QSOs. Their X-ray spectra are often characterized by highly-ionized, complex absorbers and/or reflection from the inner accretion disk, and the relative importance of the two is currently debated. Whatever the correct interpretation may be, the presence of such features implies that we are looking at matter located in the innermost regions of these AGN. Aims. We want to clarify the nature of the X-ray emission of PG 1535+547, and constrain the physical properties of its innermost regions, where this emission originates. Methods. We present new XMM-Newton observations of PG 1535+547 (90 ks exposure time, January 2006), from which we obtained two spectra European Photon Imaging Camera (EPIC) separated by about one week. We compare these spectra with those from a previous (November 2002) XMM-Newton observation. Results. These latest observations support the complex and variable nature of the X-ray emission of PG 1535+547. The broadband observed flux increases by a factor ∼2.3 in three years, and then decreases by a factor ∼1.3 in about one week. In the new spectra, strong absorption features at E < 3 keV and a complex spectral shape in the iron-line energy range are evident, coupled with a drop in the emission at higher energies. We describe all the different states in a consistent way, assuming either a warm absorber plus a relativistically-blurred ionized reflection, or a two-phase warm absorber partially covering the source with the addition of a scattered component. Conclusions. The observed variability can be ascribed mostly to warm absorbing gas in the innermost regions of PG 1535+547, which appears to vary in its physical properties on timescales of both years and days. In the blurred reflection scenario, all the analyzed states require a high fraction of reflection from the disk, calling for some mechanisms able to increase the reflection component with respect to the intrinsic continuum. Finally, the strong variability observed in the X-ray band opposed to a more constant emission at optical frequencies, changes the value of the X-ray-to-optical spectral index, implying that PG 1535+547 can not actually be classified as a soft X-ray weak active galactic nucleus (AGN).