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I present new results from time-resolved X-ray spectroscopy of bright obscured AGNs, showing column density variability on short time-scale (from hours to a few weeks). A simple analysis of these variations shows that the circumnuclear absorber must be made of clouds with densities of the order of 1010–1011 cm-3, located at distances of the order of 104 gravitational radii from the center. This strongly suggests an identification between the X-ray absorber and the BLR clouds. [ABSTRACT FROM AUTHOR]

We constrain the number density and evolution of Compton-thick Active Galactic Nuclei (AGN), and their contribution to the extragalactic X-ray background. In the local Universe we use the wide area surveys from the Swift and INTEGRAL satellites, while for high redshifts we explore candidate selections based on mid-IR parameters. We present the properties of a sample of 211 heavily-obscured AGN candidates in the Extended Chandra Deep Field-South (ECDF-S) selecting objects with f24μm/fR>1000 and R-K>4.5. The X-ray to mid-IR ratios for these sources are significantly larger than that of star-forming galaxies and ∼2 orders of magnitude smaller than for the general AGN population, suggesting column densities of NH>5×1024 cm-2. The space density of CT AGN at z∼2 derived from these observations is ∼10-5 Mpc-3, finding a strong evolution in the number of LX>1044 erg/s sources from z = 1.5 to 2.5. [ABSTRACT FROM AUTHOR]

Discovering and studying obscured AGN at z>=1–3 is important not only to complete the AGN census, but also because they can pinpoint galaxies where nuclear accretion and star-formation are coeval, and mark the onset of AGN feedback. We present the latest results on the characterization of z = 1–3 galaxies selected for their high mid-infrared to optical flux ratio, showing that they are massive and strongly star-forming galaxies, and that many do host highly obscured AGN. We present a pilot program to push the search of moderately obscured AGN up to z = 5–6 and discuss the perspectives of this line of research. [ABSTRACT FROM AUTHOR]

The INTEGRAL mission provides a large data set for studying the hard X-ray properties of AGN and allows to test the unified scheme for AGN. We present results based on the analysis of 199 AGN. A difference between the Seyfert types is detected in slightly flatter spectra with higher cut-off energies and lower luminosities for the type 2 AGN. When applying a Compton reflection model, the underlying continua (Γ≃1.95) appear the same in Seyfert 1 and 2, and the reflection strength is R≃1 in both cases, with differences in the inclination angle only. More luminous objects appear to be more massive and there is also a general trend for the absorbed sources and type 2 AGN to have lower Eddington ratios. The number counts are consistent with no evolution of the observed AGN. The unified model for Seyfert galaxies seems to hold, showing in hard X-rays that the central engine is the same in Seyfert 1 and 2 galaxies, seen under different inclination angle and absorption. [ABSTRACT FROM AUTHOR]

There exists a population of broad-line z∼2 QSOs which have heavily absorbed X-ray spectra. These objects constitute ∼10% of the population at luminosities and redshifts characteristic of the main producers of QSO luminosity in the Universe. Our follow up observations in the submm show that these QSOs are often embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. The radically different star formation properties between the absorbed and unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus invoked in AGN unification schemes. Instead, these results suggest that the objects represent a transitional phase in an evolutionary sequence relating massive black holes and the formation of galaxies. The most puzzling question about these objects has always been the nature of the X-ray absorber. We present our study of the X-ray absorbers based on deep (50–100 ks) XMM-Newton spectroscopy. We show that the absorption is most likely due to a dense ionised wind driven by the QSO. This wind could be the mechanism by which the QSO terminates the star formation in the host galaxy, and ends the supply of accretion material, to produce the present day black hole/spheroid mass ratio. [ABSTRACT FROM AUTHOR]

We present the angular correlation function of the X-ray population of 1063 XMM-Newton observations at high Galactic latitudes, comprising up to ∼30000 sources over a sky area of ∼125 sq. degrees in the energy bands: soft (0.5–2 keV) and hard (2–10 keV). This is the largest sample of serendipitous X-ray sources ever used for clustering analysis purposes to date and the results have been determined with unprecedented accuracy. We detect significant clustering signals in the soft and hard bands (∼10σ and ∼5σ, respectively). We deproject the angular correlation function via Limber’s equation and calculate the typical spatial lengths. We infer that AGN at redshifts ∼1 are embedded in dark matter halos with typical masses of logM∼12.6 h-1 M⊙ and lifetimes in the range ∼3–5×108 years, which indicates that AGN activity is a transient phase in the life of galaxies. [ABSTRACT FROM AUTHOR]

We present initial results from a new 440-ks Chandra HETG GTO observation of the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together with Chandra’s superb spatial and spectral resolution, allow an unprecedented view of its nucleus and circumnuclear NLR. We perform the first spatially resolved high-resolution X-ray spectroscopy of the ‘ionization cone’ in any AGN, and use the sensitive line diagnostics offered by the HETG to measure the ionization state, density, and temperature at discrete points along the ionized NLR. We argue that the NLR takes the form of outflowing photoionized gas, rather than gas that has been collisionally ionized by the small-scale radio jet in NGC 1068. We investigate evidence for any velocity gradients in the outflow, and describe our next steps in modeling the spatially resolved spectra as a function of distance from the nucleus. [ABSTRACT FROM AUTHOR]

I discuss the synergies between Simbol-X and three among the major astronomical facilities that, in the next decade, will be operative in the infrared-millimeter spectral range, namely JWST, Herschel and ALMA. I first provide a brief overview of the main features and observing capabilities offered by these facilities. Then I will discuss a few research fields (mostly extragalactic) that will geatly benefit of the joint exploitation of Simbol-X and these IR-mm observatories. [ABSTRACT FROM AUTHOR]

We present preliminary results of an ongoing project devoted to the study of the continuum and Fe K band variability in a sample of bright AGNs. These kind of studies may break the spectral degeneracy between the different absorption/emission models, allowing “safe” measurements of the disc and black hole properties from the broad line shapes. In fact, the Fe K band, alone, allows a first separation between the different components. Here we show the case of NGC 3783 which shows both a constant and a variable reflection component as well as strong ionized absorption. We show that a fundamental contribution will be given by Simbol-X that will allow to simultaneously measure not only the Fe K variability, but also the connected reflection hump variations. [ABSTRACT FROM AUTHOR]

We present simultaneous optical (BVRI) and X-ray (RXTE PCA) data on the quasar 3C279 from the day of the recent VHE detection by MAGIC and discuss the implications of the snap-shot spectral energy distribution (SED) for leptonic jet models of blazars. A one-zone synchrotron-self-Compton origin of the SED up to VHE γ-rays can be ruled out. The VHE emission could, in principle, be interpreted as Compton upscattering of external radiation (e.g., from the broad-line regions) in a one-zone leptonic model. However, such an interpretation would require either an unusually low magnetic field of B∼0.03 G, or (in order to achieve approximate equipartition between magnetic field at B∼0.25 G and relativistic electrons) an unrealistically high Doppler factor of Γ∼140. In addition, such a model fails to reproduce the observed X-ray flux. We therefore conclude that a simple one-zone, homogeneous leptonic jet model is not able to plausibly reproduce the SED of 3C279 including the recently detected VHE γ-ray emission. This as well as the lag of correlated variability in the optical with the VHE γ-ray emission suggests a multi-zone model in which the optical emission is produced in a different region than the VHE γ-ray emission. Alternatively, also a hadronic origin of the VHE γ-rays seems plausible. [ABSTRACT FROM AUTHOR]

The blazar Mrk421 was observed independently, but contemporaneously, in 2005 at TeV energies by MAGIC, the Whipple 10 m telescope, and by a single VERITAS telescope during the construction phase of operations. A comparison of the time averaged spectra, in what was a relatively quiescent state, demonstrates the level of agreement between instruments. In addition, the increased sensitivity of the new generation instruments, and ever decreasing energy thresholds, questions how best to compare new observational data with archival results. [ABSTRACT FROM AUTHOR]

There are different spectroscopic methods for direct diagnostics of emitting plasma in astrophysical objects, but these methods could not be used in the case of the Broad Line Region (BLR) of Active Galactic Nuclei (AGN). Here we combine the Boltzmann-plot (BP) method [1], [2] and calculations performed with the photoionization code CLOUDY [3] in order to find a simple tool that would only use the observed broad Balmer and helium lines (HeII λ4686 and HeI λ5876) for the temperature diagnostics of the BLR. [ABSTRACT FROM AUTHOR]

XMM-Newton data analysis of the bright galaxy 4U 1344-60 is presented. The observed X-ray spectrum is complex. The continuum emission can be described as a power law obscured by two neutral absorption components. Interestingly, 4U 1344-60 exhibits a broad and skewed iron line at 6.4 keV most likely originated in a few gravitational radius from the black hole. Optical spectral analysis was also presented. On the basis of its results, we propose to classify 4U 1344-60 as a Seyfert 1.5 galaxy located at z=0.012±0.001. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Giant radio sources (GRSs), defined to be those with a projected linear size >=1 Mpc, are the largest single objects in the Universe, and are useful for probing a number of astrophysical questions. The lobes of radio emission in these sources extend for hundreds of kpc from the initial acceleration regions, called hotspots, towards the nuclear regions of their parent galaxies. Spectral studies of the lobes, as well as comparisons of radiative lifetimes with times scales of transport of plasma, suggest several cases of in situ acceleration of the radiating particles. Such studies may also help constrain different processes responsible for re-acceleration such as collisionless reconnection and Fermi-type shock acceleration. Here we present the initial results of a multifrequency study of a sample of GRSs made with the Very Large Array and the Giant Metrewave Radio Telescope. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

With the advent of the present and future spatial X-ray missions, it becomes crucial to model correctly the line spectrum of X-ray emitting/absorbing media. We have built a photoionization code, TITAN, solving the transfer of a thousand lines and of the continuum with the “Accelerated Lambda Iteration” method (ALI), which is most reliable for line transfer. We give some details about this method and a justification for its use as a complement to usual approximations (e.g., escape probability or two-stream) made at present in other codes. We show that the escape probability approximation leads to a wrong estimation of the emitted X-ray line intensities, especially in the soft X-ray range. The errors can exceed one order of magnitude in the case of thick media (Thomson thickness of the order of unity). It also happens, but for different reasons, in the case of moderately thin media (Thomson thickness of 0.001 to 0.1), characteristic of the Warm Absorber in Seyfert 1 or of the X-ray emitting medium in Seyfert 2. Using TITAN, new diagnostics based on He-like ion lines of the n=2 complex are computed and some examples are presented here, concerning in particular the influence of the transfer method on the G ratio. We show also an example of the influence of the direction on the emission/absorption spectrum. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

At least half of all Active Galaxies show the presence of strong absorption features produced by highly ionized material. These features are blueshifted, implying outflowing winds. The location of these winds is of great importance to understanding the structure of quasars. Variability of the absorption features in response to flux variations of the central source is one of the best diagnostics to constrain the location and structure of AGN winds. Here we show that the opacity in the absorber in NGC 3783 clearly changes (at a level > 10σ) in a timescale of 31 days responding to a factor of ∼ 2 change in the ionizing continuum. There is also evidence for variability in the O VI K edge (at ∼ 3σ). The observed changes are consistent with the gas producing these absorption features being close to photoionization equilibrium. The observed change in opacity implies a density > 1 × 104 cm-3, and so locates the gas within 6 pc of the X-ray source. The scenario in which the gas is composed of a continuous radial range of ionization structures is ruled out, as in such scenario, no opacity variations are expected. Rather, the structure of the absorber is likely composed of heavily clumped gas. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present full set of model atmosphere equations corresponding to an accretion disk around a supermassive black hole illuminated by hard X-ray power-law. Model equations allow for multiple Compton scattering of radiation on free electrons, and for large relative photon-electron energy exchange. We present spectra in specific intensities integrated over disk surface. Outgoing intensity spectra show soft X-ray excess below 1 keV, and distinct Kα and Kβ fluorescent lines of iron. We demonstrate the existence of the Compton shoulder and claim that it can contribute to the asymmetry and equivalent widths of some observed lines in AGN. [ABSTRACT FROM AUTHOR]

Fanaroff & Riley type II radio galaxies (FRII) are complex objects. In particular FRII Narrow Line Radio Galaxies (NLRG), optically classified as High Excitation Galaxies (HEG) show X-ray spectra very similar to their radio-quiet counterparts, the Seyfert 2 galaxies. They show 2–10 keV continua heavily obscured (NH∼1023–24 cm-2) and intense FeKα lines, typical cold matter reprocessing features. Moreover recent Chandra and XMM-Newton observations suggest that the soft X-ray emission of HEG and Seyfert 2 have a common origin from photoionized gas, reinforcing the idea that not only their nuclear engine but also the circumnuclear gas (at least the warm phase) are similar. On the contrary, our knowledge of NLRG HEG above 10 keV is very poor when compared to brighter Seyfert 2. As a consequence, the physical properties of the cold phase of the circumnuclear gas (possibly linked to a dusty torus) are largely unknown. Thanks to its high sensitivity up to 80 keV, Simbol-X will provide very accurate spectra and will allow a direct comparison between the NLRG and Seyfert 2 cold environments. [ABSTRACT FROM AUTHOR]

The MOJAVE sample is the first large radio-selected, VLBI-monitored AGN sample for which complete X-ray spectral information is being gathered. We report on the status of Swift survey observations which complement the available archival X-ray data at 0.3–10 keV and in the UV with its XRT and UVOT instruments. Many of these 133 radio-brightest AGN in the northern sky are now being observed for the first time at these energies. These and complementary other multi-wavelength observations provide a large statistical sample of radio-selected AGN whose spectral energy distributions are measured from radio to gamma-ray wavelengths, available at the beginning of GLAST operations in 2008. Here, we report the X-ray spectral characteristics of 36 of these previously unobserved MOJAVE sources. In addition, the number of MOJAVE sources detected by the BAT instrument in the hard X-ray band is growing: we report the detection of five new blazars with BAT. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present a study of the properties of obscured Active Galactic Nuclei (AGN) detected in the CDFS 1Ms observation and their host galaxies. We limited the analysis to the MUSIC area, for which deep K-band observations obtained with ISAAC@VLT are available, ensuring accurate identifications of the counterparts of the X-ray sources as well as reliable determination of photometric redshifts and galaxy parameters, such as stellar masses and star formation rates. Among other findings, we found that the X-ray selected AGN fraction increases with the stellar mass up to a value of 30% at z>1 and M*>3×1011 M. [ABSTRACT FROM AUTHOR]

We exploited the 2XMM catalog and archival products to investigate the properties of the Fe Kα line at different redshifts. Individual source spectra are stacked in different redshift and luminosity bins over the range 0

There is now mounting evidence that complexity in the obscuration of AGN may be the rule rather than the exception. We therefore propose to modify the Unification Model, adding to the torus the presence of two further absorbers/emitters. Their combination along the line of sight can reproduce all the observed phenomenology. [ABSTRACT FROM AUTHOR]

Blazars are a small fraction of all extragalactic sources but, unlike other objects, they are strong emitters across the entire electromagnetic spectrum. Available data at microwave frequencies allow for systematic studies of blazars over large cosmological volumes. At these frequencies the contamination from radio extended components with steep spectra is no longer present and the emission from the accretion process is negligible. Moreover, in the first 3 months of scientific operations Fermi-LAT detected 106 bright, high-galactic latitude (|b|>10 deg) AGNs with high significance. In this study we investigate the possible relations between the microwave and the gamma-ray emissions for Fermi-LAT detected AGNs belonging to WMAP 5th year bright source catalog. [ABSTRACT FROM AUTHOR]

Galaxy environment is expected to play a role in triggering AGN activity. We present preliminary analysis on a sample of AGN selected to have an host galaxy stellar mass above 3×1010M⊙, and L(2–10 keV)>1043 erg/s in the Chandra-Cosmos survey. We study the AGN fraction versus environment. We find that the high density environment is suppressing AGN activity by z∼1.2. [ABSTRACT FROM AUTHOR]

We discuss the fueling of the central black hole in active galactic nuclei (AGN) in the framework of a clumpy accretion flow. Shocks between elements (clumps) forming the accretion flow are at the origin of the observed radiation. We expect a cascade of shocks, with optically thick shocks giving rise to optical/UV emission and optically thin shocks accounting for the X-ray emission. We associate the characteristic X-ray variability time scale derived within our model with the break time scale observed in the X-ray power spectral density (PSD). The predicted dependence of the variability time scale on black hole mass and accretion rate is in agreement with the observational relation obtained by McHardy et al. (2006). We further discuss X-ray spectral properties, in particular we compare the predicted hard X-ray power law slope with observations. Model results are able to reproduce the range of photon index typically measured in Seyfert galaxies and may account for the observed correlation between photon index and normalized accretion rate. [ABSTRACT FROM AUTHOR]

Outflows in Active Galactic Nuclei (AGN) play an important role in the evolution of their host galaxy and on the enrichment of the intergalactic medium. In the X-ray range, the outflows appear as a warm absorber (WA) gas displaying high bulk velocities. The Absorption Measure Distribution (AMD) method provides a new handle on constraining the physics of the WA. Here, we report on the theoretical interpretation of an AMD analysis of the Seyfert galaxy NGC 3783. Computations in constant total pressure performed with the transfer-photoionization code TITAN allow us to reproduce the WA gas ionic column-densities by adjusting some important plasma parameters, e.g., the ionization parameter (ξ), the total column density (NH) or the amount of micro-turbulence. Results from both the AMD method and the TITAN code suggest the presence of a region where thermal instabilities are observed. This is compatible with the hypothesis of the WA being a clumpy, two-phase medium with colder, dense clouds embedded in a hotter, diffuse gas. [ABSTRACT FROM AUTHOR]

We present results from observations of three type 2 quasar candidates with Suzaku and XMM-Newton. These are type 2 ULIRGs with quasar classification selected from the IRAS 1 Jy sample. We analyze their X-ray spectra to investigate the AGN power in these ULIRGs. The X-ray spectra are explained by a combination of unabsorbed and absorbed power-law components with Γ = 1.48–2.40. The best-fit NH for the absorbed component is in the range of (9.1–76)×1022 cm-2. The absorption-corrected L2-10 keV of AGNs are in the range for Seyferts ((4.3–24)×1042erg s-1). [ABSTRACT FROM AUTHOR]

We present a detailed X-ray spectral analysis of 401 bright sources in the Chandra-COSMOS catalogue with >80 net counts in the 0.5–7 keV band. For 294 sources, with available XMM-Newton spectra with >80 net counts, we performed an indipendent spectral fit of XMM-Newton data, in order to compare the results and look for variability of fit parameters. Finally we performed the simultaneous fit of Chandra and XMM-Newton spectra. The main results concern the distribution of photon index Γ, the nature of the population of sources classified as passive galaxies from the optical/IR SED, but hosting an obscured AGN, and the mismatch between Chandra and XMM-Newton determination of column density. [ABSTRACT FROM AUTHOR]