The connection between active galactic nuclei (AGN) and their hosts showed to be important for understanding the formation and evolution of active galaxies. Using X–ray and deep optical data, we study how morphology and colours are related to X–ray properties at redshifts z≤2.0 for a sample of > 300 X–ray detected AGN in the Subaru/XMM-Newton Deep Survey (SXDS; Furusawa et al. 2008) and Groth-Westphal Strip (GWS; Pović et al. 2009) fields. We performed our morphological classification using the galSVM code (Huertas-Company et al. 2008), which is a new method that is particularly suited when dealing with high-redshift sources. To separate objects between X–ray unobscured and obscured, we used X–ray hardness ratio HR(0.5-2 keV/2-4.5 keV). Colour-magnitude diagrams were studied in relationship to redshift, morphology, X–ray obscuration, and X–ray-to-optical flux ratio. Around 50% of X–ray detected AGN at z≤2.0 analysed in this work reside in spheroidal and bulge-dominated galaxies, while at least 18% have disk-dominated hosts. This suggests that different mechanisms may be responsible for triggering the nuclear activity. When analysing populations of X–ray detected AGN in both colour-magnitude (CMD) and colour-stellar mass diagrams (Figure 1), the highest number of sources is found to reside in the green valley at redshifts ≈ 0.5–1.5. For the first time we studied CMD of these AGN in relation to morphology and X–ray obscuration, finding that they can reside in both early- and late-type hosts, where both morphological types cover similar ranges of X–ray obscuration (Figure 1). Our findings appear to confirm some previous suggestions that X–ray selected AGN residing in the green valley represent a transitional population (e.g. Nandra et al. 2007, Silverman et al. 2008, Treister et al. 2009), quenching star formation by means of different AGN feedback mechanisms and evolving to red-sequence galaxies. More details on analysis and results presented here can be found in Pović et al. 2012.

We present the main results of statistical study of general properties of isolated AGN hosts and AGN hosts in pairs at z<0.05 as concerns with the environmental influence on the nuclear galaxy activity. With this aim we compiled the sample of 61 isolated AGNs selected from 2MIG Catalog and Catalog Veron+2010, and the sample of 109 AGNs in pairs selected from NED database.

We found a significant excess content of Sy 2 type galaxies in comparison with Sy 1 type galaxies in both samples (44% and 11% among isolated AGNs, 48% and 6% among AGNs in pairs, respectively). Isolated AGN hosts of all spectral types are located, in average, at the more far distances and have a more complicated structure than AGNs in pairs as well as they are mostly of late morphological types. Our statistical analysis shows that the observed nuclear activity of isolated 2MIG AGNs during last 3 billions years and more, first of all, is connected with the internal galaxy parameters (relative mass/size, dark/visible matter content, multi-wavelength properties of gas-dust medium in accretion disks, tor's structure, central black hole mass etc.).

Recent observations reveal that a cool disk may survive in the innermost stable circular orbit (ISCO) for some black hole X-ray binaries in the low/hard state. The spectrum is characterized by a power law with a photon index Γ ~ 1.5-2.1 in the range of 2-10 keV and a weak disk component with temperature of ~ 0.2 keV. The formation of such a cool disk in the most inner region of black hole X-ray binaries at the low/hard state is investigated within the framework of disk accretion fed by condensation of hot corona. We also calculate the emergent spectra of the inner disk and corona. It's found that our model can very well explain the spectral features of GX 339-4 and Cyg X-1, in which the thin disk may exist at ISCO in the low/hard state.

Over the past twenty-five years, the technique of Doppler tomography has produced many 2D images of the accretion structures and other gas flows in a range of systems containing compact and non-compact stars, including cataclysmic variables, polars, Algols, x-ray, and gamma-ray binaries. Recent 3D images derived from the Radio astronomical Approach (RA) have revealed prominent gas motions beyond the central plane, and display the usual characteristics found in 2D images, as well as new evidence of tilted or precessing accretion disks around the mass gainer, and magnetic loop prominences and coronal mass ejections associated with the donor star. In this work, we have compared new 3D images derived from the back projection tomography technique with those derived from the RA method. In general, back projection produces sharper and more distinctive images than the RA method, thereby permitting a more detailed study of the physical properties of the accretion sources.

Radial Velocity (RV) plots of emission lines, including Hα, from non-magnetic Cataclysmic Variables (CV), are usually fit with a sin curve. This sin fit sometimes does not prove to be the best fit for some non-magnetic CVs with accretion discs. An analytical model is created based on our 3D Smoothed Particle Hydrodynamic (SPH) numerical code in order to simulate the RV curves. The observational target is WW And, a long period non-magnetic CV. The model takes into account disc ellipticity and inclination angle that provide good non-sinusoidal fits to the observed RV data.

We tested the origin of the nebular radiation in the symbiotic star AG Dra, during different levels of its activity. We modeled the broad wings of the OVI 1032, 1038 Å resonance lines and HeII 1640 Å line by the Thomson scattering process, and determined the electron-scattering optical depth, τe, of the symbiotic nebula. The increase of τe during active phases results from an increase in the accretion rate onto the white dwarf.

Gravitational microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disk structure in strongly lensed quasars. Some of the objects (like Einstein's cross) are reasonably consistent with the predictions of the standard accretion disk model. In other cases, the size of the emitting region is larger than predicted by the standard thin disk theory and practically independent on wavelength. This may be interpreted as an observational manifestation of an optically-thick scattering envelope possibly related to super-Eddington accretion with outflows.

We briefly summarize the method of simulating Sgr A* polarized sub-mm spectra from the accretion flow and fitting the observed spectrum. The dynamical flow model is based on three-dimensional general relativistic magneto hydrodynamic simulations. Fully self-consistent radiative transfer of polarized cyclo-synchrotron emission is performed. We compile a mean sub-mm spectrum of Sgr A* and fit it with the mean simulated spectra. We estimate the ranges of inclination angle θ=42°–75°, mass accretion rate Ṁ=(1.4-7.0)×10−8M⊙year−1, and electron temperature Te=(3–4)×1010K at 6M. We discuss multiple caveats in dynamical modeling, which must be resolved to make further progress.

Radiation of supersoft X-ray sources (SSS) dominates both the supersof X-ray and the far-UV domain, and can be detected also within the optical/near-IR wavelengths. To determine fundamental parameters of SSSs, a multiwavelength approach in modeling their spectra is essential. By this way, the basic physical parameters of a SSS (the temperature, radius, luminosity and column density of the neutral hydrogen) can be determined unambiguously. Here I demonstrate this case for the symbiotic X-ray binary RXJ0059.1-7505 (LIN 358) in the Small Magellanic Cloud (SMC).

We test observational consequences of primordial Kerr superspinars indicated by string theories. We demonstrate that Kerr superspinars can serve as ultra-high energy accelerators and explore specific optical phenomena related to accretion discs orbiting them.

Using known frequencies of the twin peak high-frequency quasiperiodic oscillations (HF QPOs) and known mass M of the central black hole, the black-hole dimensionless spin a can be determined assuming a concrete version of the resonance model. However, large range of observationally limited values of the black hole mass implies a low precision of the spin estimates. We discuss the possibility of higher precision of the black hole spin a measurements in the framework of multi-resonance model inspired by observations of more than two HF QPOs in some black hole sources. We determine the spin and mass dependence of the twin peak frequencies with a general rational ratio n:m assuming a non-linear resonance of oscillations with the epicyclic and Keplerian frequencies or their combinations. In the multi-resonant model, the twin peak resonances are combined properly to give the observed frequency set. We focus on the special case of duplex frequencies, when the top, bottom, or mixed frequency is common at two different radii where the resonances occur giving triple frequency sets.

We present a Resonant Switch (RS) model of twin peak high-frequency quasi-periodic oscillations (HF QPOs), assuming switch of twin oscillations at a resonant point, where frequencies of the upper and lower oscillations νU and νL become to be commensurable and the twin oscillations change from one pair of the oscillating modes (corresponding to a specific model of HF QPOs) to some other pair due to non-linear resonant phenomena. The RS model enables to determine range of allowed values of spin a and mass M of the neutron star located at the atoll source 4U 1636-53 where two resonant points are observed at frequency ratios νU : νL = 3:2, 5:4.

We consider twin-peak quasi-periodic oscillations (QPOs) observed in the accreting low-mass neutron star (NS) binaries and explore restrictions to NS properties that are implied by various QPO models. For each model and each source, the consideration results in a specific relation between the NS mass M and the angular-momentum j rather than in their single preferred combination. Furthermore, the inferred restrictions on NS properties (or QPO models) are weaker for the low-frequency sources than for the high-frequency sources.

Type Ia supernovae (SNe Ia) are the best cosmological distance indicator, however, there is still no agreement on the nature of their progenitors. There are mainly two progenitor scenarios, i.e., the single degenerate (SD) and double degenerate (DD) scenarios. In this article, we introduced our binary evolution models of various progenitor scenarios. We also obtained many properties of the surviving companions from various SD systems, which may be helpful for identifying SN Ia progenitor model. At present, it seems likely that more than one progenitor model may be required to explain the observed diversity of SNe Ia.

We report the discovery of the first ‘X’-shaped double-double radio galaxy (DDRG), MRC0929+164 (J0932+1611), from FIRST radio survey. The intersection angle of the lines of two pairs of radio lobes is around 20.6° for this object, much larger than other DDRGs. This unusual morphology may be a hint that the growth of its central super-massive black hole suffered a violent galaxy merger once.

We use data on twin kHz QPOs and measured neutron star (NS) masses to test the relation between the lower (ν1) and upper (ν2) peak frequencies predicted with the MHD Alfvén wave oscillation model (AWOM) and the general relativistic precession model (GRPM). In the context of AWOM, the NS radius can be constrained from kHz QPO data and a measured NS mass.

With kilohertz quasi-periodic oscillation (kHz QPO) sources in neutron star low mass X-ray binaries (NS-LMXBs) published up to now, we analyze the centroid frequency (ν) distribution of twin kHz QPOs. We find that Atoll and Z sources show the similar distributions of ν1 and ν2, which indicate that twin kHz QPOs may be the common property of NS-LXMBs and have the similar physical origins. The mean values of ν1 and ν2 in Atoll sources are higher than those in Z sources, and we consider that this may because the QPO signals are sheltered by the thicken accretion disk or corona in Z sources. The maximums of ν2 in both Atoll and Z sources are the same order as the Keplerian orbital frequency of the NS surface, so kHz QPOs could occur near the NS surface.

We examine the innermost 100 parsec scale region of the Seyfert 2 galaxy NGC 1068 using a high spatial resolution X-ray image obtained with the Chandra X-ray Observatory, which allows comparison between X-ray emission clumps, optical narrow line ([OIII]) clouds and sub-arcsecond scale radio jet. Based on the combined X-ray, [OIII], and radio continuum morphology, we identify the locations of intense radio jet-cloud interaction. The [OIII] to soft X-ray ratios show that some of these clouds are strongly affected by shock heating. We estimate that the kinematic luminosity of the jet-driven shocks is 6 × 1038 erg s−1.

It is known that the Z and atoll sources are two typical types of neutron-star sources in low mass X-ray binaries (LMXBs), which present very different Q-ν relations of lower kHz QPOs. We propose that the Z and atoll sources are two different phases in the evolutionary track of neutron star in LMXBs, instead of two types of distinct sources.

Cyclotron resonance scattering features (CRSF) are the direct observational evidence for the strongly magnetized neutron stars. Since the first detection of the absorption line in the X-ray source Her X-1 thirty years ago, more than ten sources are indentified as the strongly magnetized neutron stars through detecting CRSFs. INTEGRAL is the new X-ray/gamma-ray mission with good angular resolution, high sensitivity and spectral resolution in the range of 18 C 200 keV, so that it provides us a good chance to detect the CRSFs in neutron star systems. INTEGRAL has confirmed the line features in 5 previous known sources and discovered 4 new candidates. Physical mechanism of CRSFs and accretion physics can be probed with detailed spectral analysis.