The excellent spatial resolution of the Chandra satellite allowed us to see a wide variety of new types of substructures in the intergalactic gas in clusters of galaxies. The most promising scenarios to explain at least some of the phenomenology in the clusters centers involve processes that result from the interaction of the central active galaxy and its surroundings. Here, we present preliminary results of a Chandra velocity analysis of the Centaurus cluster. The results suggest that some of the core features may be interacting with pre-existent bulk gas flows in the cluster.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

MRC B1221–423 is a powerful, nearby (z = 0.17) compact radio source, which lies within the envelope of a galaxy which is undergoing a tidal interaction with a companion. Broad-band optical/NIR colours show evidence of several distinct episodes of star formation. The evidence points to this being a radio source “caught in the act” of its first ignition.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We determine a location of a source of a main acceleration of relativistic particles during the flare on July 14, 2000, adopting that the time of acceleration coincides with a burst of the hard linear and continuum gamma-radiation. The process of this effective acceleration starts when one of flare ribbons reaches the large spot of the group, as it follows from the TRACE data. An estimation shows that the source of acceleration locates on the height of 15–20 thousands of km above the photosphere. Comparison these results with those for other large flares allows us to conclude that during almost 30 powerful events in the last three cycles an additional effective “accelerator” of a moderate scale turns on in diluted regions with large magnetic fields and their gradients.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the catalog of data for 27 gamma-ray flares detected above 500 keV by the gamma-ray spectrometer SONG (Solar Neutrons and Gamma-Rays) onboard the Russian CORONAS-F satellite. These gamma-ray flares were collected during the period from August 14, 2001 till November 31, 2003 covering the latter half of the 23rd solar sunspot cycle.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present new observations from Gemini-South for two unusual AGNs: the recently-discovered, largest-known FR I radio galaxy (>1.1 Mpc), and a FR I radio galaxy originating from a spiral host (the wrong kind of galaxy!). Both AGNs may represent missing classes of objects, not present in current surveys and samples.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The relaxation dynamics of a magnetized plasma system is a subject of fundamental importance in MHD – with applications ranging from laboratory plasma devices like the Toroidal Field Pinch and Spheromaks to astrophysical plasmas, stellar flaring activity and coronal heating. Taylor in 1974 proposed that the magnetic field in a plasma (of small but finite resistivity) relaxes to a minimum energy state, subject to the constraint that its total magnetic helicity is conserved (Woltjer 1958), such that the final magnetic field configuration is a constant $\alpha$ (linear) force-free field – where $\alpha$ is a quantity describing the twist in magnetic field lines. However, a clear signature of this mechanism in astrophysical plasmas remained undetected. Here we report observational detection of a relaxation process, similar to what Taylor (1974, 1986) envisaged, in the magnetic fields of flare-productive solar active regions. The implications of this result for magnetic reconnection and the coronal heating problem are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Studies in optical starlight have failed to reach a consensus on the importance of either galaxy interactions, bars, or nuclear spirals in triggering luminous active galactic nuclei (AGNs). Here, we present the first systematic imaging study of Seyfert (disk) galaxies in the 21-cm line of neutral atomic hydrogen (HI) gas. HI is the most sensitive and enduring tracer of galaxy interactions, and can reveal tidal features not otherwise visible in optical starlight. Our sample comprises all twenty-eight galaxies in the Véron-Cetty & Véron (1998) catalog with nuclear magnitudes −19 ≥ MB > −23 (including Seyfert, LINER, and HII galaxies) at 0.015 ≤ z ≤ 0.017 in the northern hemisphere, and a matched control sample of twenty-seven inactive galaxies at z≈0.008. We have detected nearly all the galaxies observed, and find a much higher incidence of tidal interactions — usually not seen in optical starlight — among the Seyfert galaxies by comparison with the matched control sample. Those Seyferts with uncertain or no clear tidal features show disturbed HI morphologies and/or kinematics, as well as HI companion galaxies, more frequently than the control sample. Our study suggests that the undisturbed optical appearence of active galaxies may be deceptive, and imply that galaxy-galaxy interactions trigger a significant fraction luminous AGNs at low redshifts. The majority of the Seyfert galaxies in our sample appear to be at a relatively early stage of an encounter rather than late in a merger.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have compared galaxies hosting an active nucleus with non-active galaxies in the SDSS by analyzing their stellar populations. We conclude that the Seyfert 2 phenomenon appears in galaxies of intermediate masses (∼2 × 1010 M$_\odot$), while low mass galaxies do not produce active nuclei, and high mass galaxies tend to produce a low level of non-stellar activity. We also compared the environment of active and non-active galaxies of similar masses and concluded that there is no excess of close neighbors among the Seyferts when compared with non-active galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The CORONAS-F satellite has been launched on 31 July 2001 (Oraevsky et al. 2002). To conduct measurements of the intensity of solar radiation in the EUV spectral region near the hydrogen line $L_{\alpha}(\lambda = 121.6$ nm) the spectrophotometer VUSS was installed onboard CORONAS-F. A vacuum photodiode was used as EUV detector in VUSS with the $CuJ$ cathode and $MgF_2$ entrance window.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Results of modern multi-wavelength observations of large solar non-stationary events are briefly summarized. Such events consist of a puls, an eruption (surge or CME) and a long-living system of giant arches.

Observations demonstrate often that the pulse arises as a result of “avalanche” of interaction of small-scale magnetic elements, while the dynamic system transforms into a state of self-organizing criticality (SOC) on the post-eruptive phase. We developed new code for the avalanche model where it is possible to consider a transition of the active region as a dynamic system in a state of SOC. Derived solutions show, firstly, that the avalanche is naturally developed nearby spots during the pulse. Secondly, during long-duration events, occuring along the neutral line of the longitudinal magnetic field, behaviour of the large-scale coronal magnetic field is characterized by a state of SOC.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study AGN jet formation by means of exact solutions of the relativistic magnetohydrodynamic equations. This is an original extension in Schwarzchild's metric of previous meridionally self-similar models. The outflow is mainly thermally driven to high asymptotic speeds from the central region where the escape speed is also high. The jet solutions are magnetically collimated on the sub-parsec scale.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The paper is devoted to the coronal bright points. We carried out the analysis of the simultaneous observations in IR He $\lambda$10830 Å and microwaves at 5.2 and 1.76 cm. It was obtained that microwave sources correspond to the dark points in IR He $\lambda$10830 Å with line-of-sight velocities directed from a observer. The possible mechanism of the energy transport within the bright points are suggested.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present completed results of a high resolution radio imaging survey of the Palomar Spectroscopic Sample of all (∼470) nearby bright northern galaxies. Almost half the Palomar sample's galaxies have nuclei with emission-lines characteristic of AGN but with LHα ≤ 1040 erg s−1. These are referred to as low-luminosity AGNs or LLAGNs. The power source of such LLAGNs has been long debated. High resolution radio surveys of the sample – with the VLA at 15 GHz (150 mas resolution), and the VLBA at 5 GHz (2 mas resolution) – have now revealed a high incidence of pc-scale radio cores with implied brightness temperatures [gsim ]108K, and sub-parsec scale jets. The results support the presence of accreting black holes in ≥50% of all LLAGNs; there is no evidence against all LLAGNs being mini-AGNs. The detected parsec-scale radio nuclei are preferentially found in massive ellipticals and in type 1 nuclei (i.e. nuclei with broad Hα emission). These nuclei follow the usual correlations between radio and emission-line gas properties found in more powerful AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs extends three orders of magnitude below, and is continuous with, that of ‘classical’ AGNs. We find marginal evidence for a low-power turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of accretion in the local universe. Low accretion rates (≤10−2−10−3 of the Eddington rate) are implied in both advection- and jet-type models. Within the context of jet models, the accretion energy output is dominated by the energy in the observed jets rather than the radiated bolometric luminosity. These jets would be able to dump sufficient energy into the innermost parsecs to significantly slow the accretion inflow. Detailed results can be found in Nagar et al. (2002, 2004) and references therein.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Coronagraphic spectral observations carried out with UVCS on SoHO above polar coronal holes have shown that the velocity distribution is highly anisotropic. Here we examine the influence of the density stratification on the interpretation of such observations. In particular, we investigate the profiles of O VI spectral lines emitted in polar coronal holes. We find that at distances greater than $1~R_{\odot}$ from the solar surface the widths of the emitted lines are significantly affected by the details of the adopted electron density profiles. In particular, the densities deduced by Doyle et al. (1999) from SoHO data result in O VI profiles whose widths and intensity ratio are relatively close to the values observed by UVCS although only isotropic velocity distributions are employed. Hence we expect that the magnitude of the anisotropy of the velocity distribution deduced from UVCS data depends strongly on the adopted density profile.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Global three-dimensional (3D) magneto-hydrodynamical (MHD) simulations of accretion flow have been extensively performed recently. We calculate the emergent spectra from 3D MHD flows by the Monte Carlo radiative transfer simulations, and examine to what extent simulated MHD flows can account for the observed spectrum of Sagittarius A* (Sgr A*). It is found that the emergent spectrum from the inner part of the MHD flow (r<10rs) is consistent with the observations in the X-ray flaring state of Sgr A*, where rs is the Schwarzschild radius. However, the MHD flow can not reproduce the spectrum in the quiescent state.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using N-body numerical simulations, we investigate the stability of a nuclear disk of a few pc characteristic radius, around a supermassive black hole (SBH), and embedded in a galactic bulge. We find that with an SBH of a suitable range of mass, placed at its center, the nuclear disk is subject to one-armed (m=1) natural instabilities. We propose a feedback cycle for this mode, based on waves between corotation and OLR, and where the “indirect term”, and the massive bulge play a fundamental role. Nuclear disks formed from accreted gas could be the precursors of this type of structure and may be common in central regions of galaxies. Density waves could be an efficient mechanism of fueling the gas in the central few tens of parsecs in galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report on a novel investigation of the complex magnetism of the quiet Sun which is based on a realistic three-dimensional modeling of the Hanle effect.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We compare the circumnuclear stellar population and environmental properies of Seyfert and Composite (Seyfert + Starburst) nuclei with those of LINERs and LINER/HII transition galaxies (TOs), and discuss evidence for evolution from Seyfert/Composite to LINER/TO nuclei.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar corona is believed to be generally low beta. In a low-beta plasma, energy is mainly stored as magnetic energy or current. To dissipate the stored magnetic energy in the highly conductive corona, anomalous resistivity is needed. Activities of outer layers of X-ray loops in solar flares have been interpreted as the result of reconnection of magnetic field due to anomalous resistivity in a current sheet located above the flaring loop.

However, recent high-cadence EUV observations show many flares without opening up of magnetic field. This means that existence of current sheets above flaring loops is not a necessary element for flares. It is also found for many flares that low temperature prominence plasma are heated in the very early phase of lifting. These observational facts require a new solar flare scenario different from reconnection.

Recent multi-wavelength high-spatial and -temporal resolution observations show that flares originate in the lower atmosphere. We can expect high beta plasma and small curvature magnetic loops in the lower atmosphere. It is also observed high-velocity flows along magnetic loops associated with flares. Bounded motions of charged particles (both thermal motion and flow) along the magnetic lines of force create the centrifugal force. They exceed gravity force under certain conditions (small curvature and high velocity). They can even exceed magnetic tension force depending on beta values of the plasma in the loop.

In the case of the upward acceleration (centrifugal - gravity$>0$), the plasma is balanced by the magnetic tension force if the beta value is not large enough. This is a favorable condition for the interchange instability. Finite beta ($beta \sim 0.1$) plasma in a loop, whose ends are anchored at the photosphere, is unstable against the localized interchange (BALLOONING) mode. It can develop into non-linear phase and explosive phenomena are expected. This is called HIGH-BETA DISRUPTION. The high-beta disruption has many common characteristics to solar flares. Various phenomena related to solar flares such as, high-energy particle acceleration, plasma turbulence, plasma ejections, plasma heating, are interpred as the result of high-beta disruption. High spatial and temporal resolution observations of flares at various wavelengths are used to see the actual instability process. Shibasaki (2001)To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The observed properties of supermassive black holes suggest a fundamental link between their assembly and the formation of their host spheroids. We model the growth and activity of black holes in galaxies using ΛCDM cosmological hydrodynamic simulations. We study the evolution of the metal enrichment in quasar hosts and hence explore the relationship between star/spheroid formation and black hole growth/activity in galaxies. Using the simulations we approach the epoch of the first quasars and the first significant star formation activity. We show that the hosts of the rare bright quasars at z∼5−6 have star formation rates of several hundred $\rm\thinspace M_{\odot}\yr^{-1},$ and halo masses of order ∼1012$\rm\thinspace M_{\odot}$. Already at these redshifts they have supersolar ($Z/Z_{\odot} \sim 2-3$) central metallicities, with a mild dependence of metallicity on luminosity, consistent with observed trends.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html