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Local conformal symmetry introduces the conformal curvature (Weyl tensor) that gets split into its (gravito-) electric and magnetic (tensor) parts. Newtonian tidal forces are expected from the gravitoelectric field, whereas general-relativistic frame-dragging effects emerge from the gravitomagnetic field. The symmetric, traceless gravitoelectric and gravitomagnetic tensor fields can be visualized by their eigenvectors and eigenvalues. In this paper, we depict the gravitoelectric and gravitomagnetic fields around a slowly rotating black hole. This suggests that the phenomenon of ultra-fast outflows observed at the centers of active galaxies may give evidence for the gravitomagnetic fields of spinning supermassive black holes. We also question whether the current issues in our contemporary observations might be resolved by the inclusion of gravitomagnetism on large scales in a perturbed FLRW model. [ABSTRACT FROM AUTHOR]

Large scale magnetic field can be easily dragged from galactic scales toward AGN along with accreting gas. There, it can contribute to both the formation of AGN “torus” and help to remove angular momentum from the gas which fuels AGN accretion disk. However the dynamics of such gas is also strongly influenced by the radiative feedback from the inner accretion disk. Here we present results from the three-dimensional simulations of pc-scale accretion which is exposed to intense X-ray heating. [ABSTRACT FROM AUTHOR]

In this paper, we present a complete work on steady state spherically symmetric Bondi type accretion flow in the presence of cosmological constant (Λ) in both Schwarzschild-de Sitter (SDS) and Schwarzschild anti-de Sitter (SADS) backgrounds considering an isolated supermassive black hole (SMBH), with the inclusion of a simple radiative transfer scheme, in the pseudo-general relativistic paradigm. We do an extensive analysis on the transonic behavior of the Bondi type accretion flow onto the cosmological BHs including a complete analysis of the global parameter space and the stability of flow, and do a complete study of the global family of solutions for a generic polytropic flow. Bondi type accretion flow in SADS background renders multiplicity in its transonic behavior with inner "saddle" type and outer "center" type sonic points, with the transonic solutions forming closed loops or contours. There is always a limiting value for ∣Λ∣ up to which we obtain valid stationary transonic solutions, which correspond to both SDS and SADS geometries; this limiting value moderately increases with the increasing radiative efficiency of the flow, especially correspond to Bondi type accretion flow in SADS background. Repulsive Λ suppresses the Bondi accretion rate by an order of magnitude for relativistic Bondi type accretion flow for a certain range in temperature, and with a marginal increase in the Bondi accretion rate if the corresponding accretion flow occurs in SADS background. However, for a strongly radiative Bondi type accretion flow with high mass accretion rate, the presence of cosmological constant do not much influence the corresponding Bondi accretion rate of the flow. Our analysis show that the relic cosmological constant has a substantial effect on Bondi type accretion flow onto isolated SMBHs and their transonic solutions beyond length-scale of kiloparsecs, especially if the Bondi type accretion occurs onto the host supergiant ellipticals or central dominant (CD) galaxies directly from ambient intercluster medium (ICM). However, for high mass accretion rate, the influence of cosmological constant on Bondi accretion dynamics, generically, diminishes. As active galactic nuclei (AGN)/ICM feedback can be advertently linked to Bondi type spherical accretion, any proper modeling of AGN feedback or megaparsecs-scale jet dynamics or accretion flow from ICM onto the central regions of host galaxies should take into account the relevant information of repulsive Λ, especially in context to supergiant elliptical galaxies or CD galaxies present in rich galaxy clusters. This could also explore the feasibility to limit the value of Λ, from the kinematics in local galactic-scales. [ABSTRACT FROM AUTHOR]

We provide a description of the latest status and performance of the Planck satellite, focusing on the final predicted sensitivity of Planck. The optimization of the observational strategy for the additional surveys following the nominal 15 months of integration (about two surveys) originally allocated and the limitation represented by astrophysical foreground emissions are presented. An outline of early and intermediate astrophysical results from the Planck Collaboration is provided. A concise view of some fundamental cosmological results that will be achieved by exploiting Planck's full set of temperature and polarization data are presented. Finally, the perspectives opened by Planck in answering some key questions in fundamental physics, with particular attention to parity symmetry analyses, are described. [ABSTRACT FROM AUTHOR]

We present a detailed statistical analysis of the alignment of polarizations of radio sources at high redshift. This study is motivated by the puzzling signal of alignment of polarizations from distant quasars at optical frequencies. We use a coordinate invariant measure of dispersion to test for alignment of polarizations of widely separated sources. The data from JVAS/CLASS 8.4 GHz surveys are used for our study. We find that the data set with polarization flux greater than 1 mJy shows a significant signal of alignment at distance scales of order 150 Mpc. The significance of alignment decreases as we go to larger distances. In contrast the data set with polarization flux less than 1 mJy does not show significant alignment at short distances. However this set, as well as the full data sample, shows a very significant signal at large distances of order 500-850 Mpc. Due to the presence of relatively large error in the low polarization sample, this signal needs to be tested further with more refined data. We also study the signal by imposing a cut on the error in polarization. We find that the significance of alignment increases with decrease in fractional error. We are unable to attribute our results to known sources of bias. We discuss a possible physical explanation of our results. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the astrophysical results and the related cosmological implications derived from recent microwave surveys, with emphasis to those coming from the Planck mission. We critically discuss the impact of systematic effects and the role of methods to separate the cosmic microwave background (CMB) signal from the astrophysical emissions and each different astrophysical component from the others. We then review the state-of-the-art diffuse emissions, extragalactic sources, cosmic infrared background and galaxy clusters, addressing the information they provide to our global view of the cosmic structure evolution and for some crucial physical parameters, as the neutrino mass. Finally, we present three different kinds of scientific perspectives for fundamental physics and cosmology offered by the analysis of on-going and future CMB projects at different angular scales dedicated to anisotropies in total intensity and polarization and to absolute temperature. [ABSTRACT FROM AUTHOR]

We have compared the parsec-scale jet linear polarization properties of the Fermi LAT-detected and non-detected sources in the complete flux-density-limited (MOJAVE-1) sample of highly beamed AGN. Of the 123 MOJAVE sources, 30 were detected by the LAT during its first three months of operation. We find that during the era since the launch of Fermi, the unresolved core components of the LAT-detected jets have significantly higher median fractional polarization at 15 GHz. This complements our previous findings that these LAT sources have higher apparent jet speeds, brightness temperatures and Doppler factors, and are preferentially found in higher activity states. [ABSTRACT FROM AUTHOR]

We have performed the first 3.5 mm polarimetric survey of radio loud active galactic nuclei (AGN) with the IRAM 30 m Telescope. Unlike radio wavelengths, millimeter observations allow us to measure the intrinsic linearly polarized emission from AGN, thanks to the marginal effect of Faraday rotation and depolarization at mm wavelengths. The sample contains 145 sources, and it essentially consists of all flat-spectrum AGN with declinations accessible to the 30 m Telescope (Dec. (J2000.0) > -30°), and with 3 mm flux density ≳ 1 Jy, as measured from 1978 to 1994. LBAS quasars in our sample show larger luminosity than non-LBAS ones, which is consistent with previous work claiming larger Doppler factors for brighter γ-ray blazars. This effect cannot be claimed for BL Lacertae objects in our sample, which suggests that only quasars contribute to distribute LBAS blazars towards larger luminosities. We find a systematic 3.5 mm linear polarization degree excess by a factor of ~ 2 with regard to the one at 2 cm for all optical and γ-ray classes of sources considered here. Our sample shows a significant trend to increase the luminosity of their jets for decreasing linear polarization fraction. Unlike previous studies in the radio spectral range, we do not find a clear relation between the linear polarization angle and the jet structural position angle of any source class in our sample. This is interpreted as a markedly non-axisymmetric character of the 3 mm emitting region of radio loud AGN jets. [ABSTRACT FROM AUTHOR]

In this work, we revisited the relationship between the subclasses of blazars (X–ray selected BL Lacertae objects (XBLs), radio selected BL Lacertae objects (RBLs), and flat spectrum radio quasars (FSRQs)) based on a sample of blazars. We found that the FSRQs–RBLs–XBLs relationship is clear in their bolometric luminosity, emission line luminosity and the accretion ratio with VFSRQs > VRBLs > VXBLs, where V stands for the three parameters. However, there is no clear difference amongst their central black hole masses. The bolometric luminosity is closely correlated with the emission line luminosity and the accretion ratio. [ABSTRACT FROM AUTHOR]

We investigate the spectral energy distribution (SED) of Centaurus A resulting from a steady compact acceleration region, located close to the central black hole, where both leptonic and hadronic relativistic populations arise. We present here results of such a model, where we have considered synchrotron radiation by primary electrons and protons, inverse Compton scattering, and gamma-ray emission originated by the inelastic hadronic interactions between relativistic protons and cold nuclei within the jets. Photo-meson production by relativistic hadrons were also taken into account, as well as the effects of secondary particles injected by all interactions. The internal and external absorption of gamma-rays is shown to be of great relevance to shape the observable SED, which was also recently constrained by the results of Fermi and HESS. [ABSTRACT FROM AUTHOR]

The recently characterized Cosmic Radio Background provides a unique perspective in which to study the nonthermal universe, including properties and cosmological evolution of active galaxies and their outflows. As much as 1/3 of the total intensity of the radio background can be due to emission resulting from classical jet processes in radio galaxies and radio quiet quasars. Furthermore, weak jet activity in Seyferts and ordinary star-forming galaxies may also be important. [ABSTRACT FROM AUTHOR]

We present a model of polarization swings in blazars from axially symmetric blobs propagating on curved trajectories. If the minimum inclination of the velocity vector to the line of sight is smaller than Γ-1, the polarization angle maximum rotation rate is simultaneous with the polarization degree minimum and a spike in the total flux. By measuring the maximum rotation rate and the moment of the polarization maximum, it is possible to estimate the distance covered by the blob and thus its approximate position. We apply this model to the recent polarization event in blazar 3C 279. [ABSTRACT FROM AUTHOR]

We present a sequence of 12 monthly polarimetric multi-frequency VLBA observations of the radio galaxy 3C 120. The motion of multiple superluminal components allows the mapping of the polarization structure along most of the jet and across its width, revealing a coherent in time Faraday screen and RM-corrected polarization angles. Gradients in Faraday rotation and degree of polarization across the jet are observed, together with a localized region of high rotation measure superposed on this structure. This is explained as produced by the presence of a helical magnetic field in a two-fluid jet model, consisting of an inner emitting jet and a sheath containing nonrelativistic electrons. Interaction of the jet with the external medium would explain the confined region of enhanced Faraday rotation. [ABSTRACT FROM AUTHOR]

The first three months of sky-survey operation with the Large Area Telescope (LAT) on board the Fermi satellite revealed 132 bright sources at |b| > 10° with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicated high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and four blazars with unknown classification. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs. Only 33 of the sources, plus two at |b| < 10°, were previously detected with EGRET, probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. Other spectral and variability blazar properties are discussed. Some prominent Fermi-detected radiogalaxies are presented. [ABSTRACT FROM AUTHOR]

Modeling implications of recent VERITAS discoveries of Intermediate BL Lac Objects (IBLs) are presented. Leptonic jet models for the IBLs W Comae (z = 0.102) and 3C 66A (z = 0.444) are, in principle, viable with only synchrotron and synchrotron self-Compton (SSC) components, but more plausible parameters can be achieved including an external infrared radiation field as source for Compton upscattering to produce the observed VHE gamma-ray emission. The unknown redshift of PKS 1424+240 makes a theoretical interpretation difficult. A pure SSC model seems to be sufficient to represent its SED, and modeling results favor a low redshift of z ≲ 0.1. [ABSTRACT FROM AUTHOR]

A time-dependent synchrotron self-Compton model (SSC) which is able to motivate the used electron spectra of many SSC models as a balance of acceleration and radiative losses is introduced. Using stochastic acceleration as well as Fermi-I processes even electron spectra with a rising part can be explained, which are mandatory to fit the low state spectral energy distribution (SED) of PKS 2155-304 as constrained from Fermi LAT observations. Due to the time resolution the outburst of PKS 2155-304 observed by H.E.S.S. in 2006 can be modelled self-consistently as fluctuations along the jet axis without introducing new sets of parameters. The model makes the time evolution of the SED also accessible, hence giving new insights into the flaring behavior of blazars. [ABSTRACT FROM AUTHOR]

The current very high energy (VHE; E > 100 GeV) experiments have tremendously increased the number of detected extragalactic sources. We present a synchrotron self-Compton modeling tour of the active galactic nuclei currently established as VHE emitters so far, and investigate possible correlations among the intrinsic and derived parameters. [ABSTRACT FROM AUTHOR]

The leptonic model has become the standard method of fitting the multiwavelength spectra of blazars. In what follows we review the basic premises of the model, giving emphasis on the evolution of its key ideas and assumptions. [ABSTRACT FROM AUTHOR]

All galaxies beyond the Magellanic clouds with detected H2O maser emission so far are investigated and their X-ray observations are collected in detail to probe the X-ray properties of this special kind of galaxies. The soft excess and the strong iron emission line are commonly presented in their X-ray spectrum. Similar to the spectra of normal Seyfert 2 galaxies, the X-ray soft components are usually explained well by two alternative models or their combination: the absorbed power law model and the thermal emission model. The hard X-ray continua are usually flat, which should be caused by the increase of the reflection component, with the increase of the absorbing material density. Modeling their X-ray spectra shows that high absorbing column density is prevalent in our H2O megamaser host AGNs. Further, we investigate a possible relation between the iron line emission and the nuclear X-ray emission. It shows no significant correlation between the equivalent width (EW) of the neutral FeKα emission line (~ 6.4 keV) and the intrinsic nuclear X-ray luminosity. However, one trend appears clearly — the EW of the iron line decreases with the increase of the observed X-ray luminosity for our H2O maser galaxies. We also estimate the accretion rate of H2O maser host AGNs and the results show that maser galaxies may have a higher accretion rate than nonmaser Seyfert galaxies. In addition, possible relations between the EW of the iron line with the accretion rate and the central black hole mass are investigated and no significant trend of correlation can be found between them. [ABSTRACT FROM AUTHOR]

Spectral line profiles produced in an outflow near a neutron star or a black hole can be strongly influenced by gravitational redshifting and by Doppler shifting due to a global motion of plasma. We consider a scenario in which a resonant absorption in a spectral line takes place in the outflowing plasma within several tens of Schwarzschild radii from a compact object. The main goal of this work is to show that under certain conditions a combination of the gravitational redshifting and Doppler blue/redshifting may produce line profiles which can be considered as "fingerprints" of the gravitational field of the compact object, much as P-Cygni profiles are "fingerprints" of stellar winds. [ABSTRACT FROM AUTHOR]

We introduce the use of a well-known parameter, the Alfvén Radius, RA, as a new tool to discern whether an X-ray binary system may undergo a microquasar phase, i.e. ejecting relativistic particles orthogonal to the accretion disk. We study what we call the basic condition, RA/R* = 1 in its dependency on the magnetic field strength and the mass accretion rate. With this basic condition we establish under which combination of parameters any class of accreting neutron stars could become a microquasar instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for an X-ray pulsar. In the case of black-hole accreting binaries we equate the magnetic field pressure to the plasma pressure in the last stable orbit (i.e. RA/RLSO = 1) and we get upper limits for the magnetic field strength as a function of the mass accretion rate and the black hole mass. [ABSTRACT FROM AUTHOR]

The high-frequency-peaked BL Lac PKS 2155-304 is one of the brightest and best-studied VHE gamma-ray sources in the southern hemisphere. Since 2002, the High Energy Stereoscopic System (H.E.S.S.) has monitored this source and found it to be in an unusually high state in July 2006. On the nights of 28 and 30 July, two major outbursts occurred, with peak fluxes ~ 80 times the usual values and well-resolved structures varying on time scales of ~ 200 s. Here, we report on spectral variability studies of VHE data of the first flare and show first results of the H.E.S.S. observations during the second flare night. [ABSTRACT FROM AUTHOR]

The quasar 3C 279 was the target of an extensive multiwavelength monitoring campaign from January through April 2006, including an optical-IR-radio Whole Earth Blazar Telescope (WEBT) campaign and Target of Opportunity X-ray and soft γ-ray observations with Chandra and INTEGRAL in mid-January 2006, with additional X-ray coverage by RXTE and Swift XRT as well as independent very-high-energy (VHE) γ-ray observations by MAGIC, which led to the first-ever reported tentative detection of a quasar at VHE γ-rays. In this paper we summarize the results of the WEBT campaign. The source exhibited substantial variability of optical flux and spectral shape, with a characteristic time scale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each other, while there was no obvious correlation between the optical and radio variability. In intriguing contrast to other (in particular, BL Lac type) blazars, we find a lag of shorter-wavelength behind longer-wavelength variability throughout the RVB wavelength ranges, with a time delay increasing with increasing frequency. Spectral hardening during flares appears delayed with respect to a rising optical flux. This, in combination with the very steep IR-optical continuum spectral index of αo ~ 1.5 – 2.0, may indicate a highly oblique magnetic field configuration near the base of the jet, leading to inefficient particle acceleration and a very steep electron injection spectrum. An alternative explanation through a slow (time scale of several days) acceleration mechanism would require an unusually low magnetic field of B < 0.2 G, about an order of magnitude lower than inferred from previous analyses of simultaneous SEDs of 3C 279 and other FSRQs with similar properties. [ABSTRACT FROM AUTHOR]

On the night of 29–30 July 2006, a major γ-ray outburst occurred from PKS 2155-304, which was observed simultaneously with H.E.S.S., Chandra and the Bronberg optical telescopes. An overall 6–8 hours of simultaneous uninterrupted coverage was obtained. Here we report the first preliminary results of this exceptional dataset. The source showed correlated variability between the X-ray and VHE bands, with no lags. The spectra evolve with similar patterns. Huge VHE variations (~ 22×) are accompanied only by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (LC/LS ~ 10), and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge all known "standard" scenarios for the blazar emission. [ABSTRACT FROM AUTHOR]

We present the results from multiwavelength campaigns of three powerful gamma-ray quasars, PKS 1510-089, RBS 315 and Swift J0746.3+2548, recently organized with Suzaku. The Suzaku observation provided one of the highest S/N X-ray spectra ever reported between 0.3 and 50 keV. For these quasars, the X-ray spectrum is well represented by an extremely hard power-law with photon index Γ ≃ 1.2, but is augmented by an additional soft component apparently below 1 keV for PKS 1510-089, whereas a strong deficit of soft photons is observed in RBS 315. We model the broadband spectra of these powerful quasars and argue that the power of the jet is dominated by protons but with the number of electrons/positrons exceeding the number of protons by a factor ≃ 10. We also argue that an extremely hard X-ray spectra may result from a double power-law form of the injected electrons, with the break energy γbr ≃ 1000 corresponding to the anticipated threshold of diffusive shock acceleration. [ABSTRACT FROM AUTHOR]

Multi-frequency (4.6, 5, 5.5, 8, 8.8, 13, 15, 22 & 43 GHz) polarization observations of six "blazars" were obtained on the American Very Long Baseline Array (VLBA) over a 24-hr period on 2 July 2006. Observing at several frequencies, separated by short and long intervals, enabled reliable determination of the distribution of Faraday rotation on a range of scales. In all cases the magnitude of the RM increases in the higher frequency observations, implying that the electron density and/or magnetic field strength is increasing as we get closer to the central engine. After correcting for Faraday rotation, the polarization orientation in the jet is either parallel or perpendicular to the jet direction. A transverse rotation measure (RM) gradient was detected in the jet of 0954+658, providing evidence for the presence of a helical magnetic field surrounding the jet. For three of the sources (0954+658, 1418+546, 2200+420), the sign of the RM in the core region changes in different frequency-intervals, indicating that the line-of-sight component of the magnetic field is changing with distance from the base of the jet. We suggest an explanation for this in terms of bends in a relativistic jet surrounded by a helical magnetic field; where there is no clear evidence for pc-scale bends, the same effect can be explained by an accelerating/decelerating jet. [ABSTRACT FROM AUTHOR]

The radio galaxy M87 has recently been found to be a rapidly variable TeV emitting source. We analyze the implications of the observed TeV characteristics and show that it proves challenging to account for them within conventional acceleration and emission models. We discuss a new pulsar-type scenario for the origin of variable, very high energy (VHE) emission close to the central supermassive black hole and show that magneto-centrifugally accelerated electrons could efficiently Compton upscatter sub-mm ADAF disk photons to the TeV regime, leading to VHE characteristics close to those observed. This suggests, conversely, that VHE observations of highly under-luminous AGNs could provide an important diagnostic tool for probing the conditions prevalent in the inner accretion disk of these sources. [ABSTRACT FROM AUTHOR]

M 87 is the first extragalactic source detected in the TeV γ-ray domain that is not a blazar, its large scale jet not being aligned to the line of sight. We present here a multi-blob synchrotron self-Compton model accounting explicitly for large viewing angles and moderate Lorentz factors as inferred from magnetohydrodynamic simulations of jet formation, motivated by the detection of M 87 at very high energies (VHE; E > 100 GeV). Predictions are presented for the very high-energy emission of active galactic nuclei with extended optical or X-ray jet, which could be misaligned blazars but still show some moderate beaming. We include predictions for 3C 273, Cen A and PKS 0521–36. [ABSTRACT FROM AUTHOR]

Photon breeding in relativistic jets involves multiplication of high-energy photons propagating from the jet into the external environment and back, with the conversion into electron-positron pairs. The exponential growth of the energy density of these photons is a supercritical process powered by the bulk energy of the jet. The efficient deceleration of the jet outer layers creates a structured jet morphology with a fast spine and slow sheath. In initially fast and high-power jets even the spine can be decelerated efficiently leading to very high radiative efficiencies of conversion of the jet bulk energy into radiation. The decelerating, structured jets have angular distribution of radiation significantly broader than that predicted by a simple blob model with a constant Lorentz factor. This reconciles the discrepancy between the high Doppler factors determined by the fits to the spectra of TeV blazars and the low apparent velocities observed at VLBI scales as well as the low jet Lorentz factors required by the observed statistics and luminosity ratio of Fanaroff-Riley I radio galaxies and BL Lac objects. Photon breeding produces a population of high-energy leptons in agreement with the constraints on the electron injection function required by spectral fits of the TeV blazars. Relativistic pairs created outside the jet and emitting gamma-rays by the inverse Compton process might explain the relatively high level of TeV emission from the misaligned jet in the radio galaxies. The mechanism reproduces basic spectral features observed in blazars including the blazar sequence (shift of the spectral peaks towards lower energies with increasing luminosity). The mechanism is very robust and can operate in various environments characterized by the high photon density. [ABSTRACT FROM AUTHOR]

In powerful cosmic nonthermal radiation sources with dominant magnetic-field self generation, the generation of magnetic fields at almost equipartition strength by relativistic plasma instabilities operates as fast as the acceleration or injection of ultra-high energy radiating electrons and hadrons in these sources. Consequently, the magnetic field strength becomes time-dependent and adjusts itself to the actual kinetic energy density of the radiating electrons in these sources. This coupling of the magnetic field and the magnetic field energy density to the kinetic energy of the radiating particles changes both the intrinsic temporal evolution of the relativistic particle energy spectrum after injection and the synchrotron and synchrotron self-Compton emissivities. [ABSTRACT FROM AUTHOR]

Supercriticality of the same kind as that in a nuclear pile can take place in high-energy astrophysical objects producing a number of impressive effects. For example, it could cause an explosive release of the energy of a cloud of ultrarelativistic protons into radiation. More certainly, supercriticality should be responsible for energy dissipation of very energetic relativistic fluids such as ultrarelativistic shocks in gamma-ray bursts and jets in active galactic nuclei (AGNs). In this case, the photon breeding process operates. It is a kind of converter mechanism with the high-energy photons and e+e- pairs converting into each other via pair production and inverse Compton scattering. Under certain conditions, which should be satisfied in powerful AGNs, the photon breeding mechanism becomes supercritical: the high-energy photons breed exponentially until their feedback on the fluid changes its velocity pattern. Then the system comes to a self-adjusting near-critical steady state. Monte-Carlo simulations with detailed treatment of particle propagation and interactions demonstrate that a jet with a Lorentz factor Γ ≈ 20 can radiate away up to a half of its total energy, and for Γ = 40 the radiation efficiency can be up to 80 per cent. Outer layers of the jet decelerate down to a moderate Lorentz factor 2–4, while the spine of the jet has a final Lorentz factor in the range 10–20 independent of the initial Γ. Such sharp deceleration under the impact of radiation must cause a number of interesting phenomena such as formation of internal shocks and an early generation of turbulence. [ABSTRACT FROM AUTHOR]

We consider some implications of the rapid X-ray and TeV variability observed in M87 and the TeV blazars. We outline a model for jet focusing and demonstrate that modest radiative cooling can lead to recollimation of a relativistic jet in a nozzle having a very small cross-sectional radius. Such a configuration can produce rapid variability at large distances from the central engine and may explain recent observations of the HST-1 knot in M87. Possible applications of this model to TeV blazars are discussed. We also discuss a scenario for the very rapid TeV flares observed with H.E.S.S. and MAGIC in some blazars, that accommodates the relatively small Doppler factors inferred from radio observations. [ABSTRACT FROM AUTHOR]

X-ray observations of Seyfert galaxies and quasars currently provide the most powerful way to study the environments of supermassive black holes. Our ability to probe these environments, some of the most extreme found in nature, is rapidly improving driven by dramatic advances in X-ray spectroscopic instrumentation. In addition to the well known 'hard X-ray power law' that is probably formed in a hot 'corona' above a cooler accretion disc, substantial spectral complexity has also been revealed. For example, soft X-ray excess emission above the power law is often seen at low X-ray energies, and this emission is thought to be associated with the inner disc. Atomic absorption/emission processes in nuclear gas flows are also observed to imprint characteristic features on X-ray spectra. Iron Kα emission lines from 6.40–6.97 keV are formed at least partially by fluorescence in the inner disc, and absorption edges seen mainly below 2 keV reveal major flows of ionized gas in the nucleus. Studies of the complex X-ray spectra of Seyferts and quasars have undergone a revolution wit the launches of Chandra in 1998 and XMM-Newton in 1999. The era of high-resolution X-ray spectroscopy has been initiated by the Chandra and XMM-Newton grating spectrometers. These detectors provide X-ray spectra with 6–100 times higher spectral resolution than those previously available, and they have dramatically enlarged the arsenal of diagnostics available for investigating Seyfert/quasar nuclei. The new generation of X-ray observatories is used to intensively address some of the leading questions about Seyfert/quasar X-ray emission. Some of the most important scientific issues for the next years are: — Matter under strong gravity: Why are relativistically blurred Fe K lines so rare? — What are the extreme X-ray spectral and variability properties of ultrasoft Narrow-Line Seyfert 1 galaxies telling us about Seyferts and quasars more generally? — What is the physical nature of the sharp spectral cut-off in Seyfert galaxies? While the advances expected from the new generation of X-ray observatories are so large and widespread that precise predictions are difficult, it is believed that particularly important progress will be made towards answering these central questions. Below is explained why the questions I have stated are fundamental and timely. [ABSTRACT FROM AUTHOR]