We perform axisymmetric simulations of two-component jet acceleration using the special relativistic MHD code PLUTO (Mignone et al., 2007). The inner, thermally driven component constitutes a dilute relativistic plasma originating in a high enthalpy central corona. The second component is a Poynting-dominated wind driven by a global current system. Once a near-stationary state is reached, we solve the polarized Synchrotron radiation transport incorporating self-absorption and (internal) Faraday rotation. With this approach we obtain high-resolution radio maps and spectra that can help in the interpretation of observational data from nearby active galactic nuclei by predicting spine-sheath polarization structures and Faraday rotation gradients.

We apply large eddy simulation technique to carry out three-dimensional numerical simulation of compressible magnetohydrodynamic turbulence in conditions relevant local interstellar medium. According to large eddy simulation method, the large-scale part of the flow is computed directly and only small-scale structures of turbulence are modeled. The small-scale motion is eliminated from the initial system of equations of motion by filtering procedures and their effect is taken into account by special closures referred to as the subgrid-scale models. Establishment of weakly compressible limit with Kolmogorov-like density fluctuations spectrum is shown in present work. We use our computations results to study dynamics of the turbulent plasma beta and anisotropic properties of the magnetoplasma fluctuations in the local interstellar medium.

The effect of the Plume/Interplume Lane (PIPL) structure of the solar North Polar Coronal Hole (NPCH) on the ion-cyclotron resonance (ICR) process is investigated. The ICR process in the interplume lanes is much more effective than in the plumes, agreeing with the observations which show the source of fast solar wind is interplume lanes.

We present an extended scheme for the calculation of the profiles of emission lines from accretion disks around rotating black holes. The scheme includes disks with angular momenta which are parallel and antiparallel with respect to the black hole's angular momentum, as both configurations are assumed to be stable (King et al. 2005). Based on a Green's function approach, an arbitrary radius dependence of the disk emissivity and arbitrary limb darkening laws can be easily taken into account, while the amount of precomputed data is significantly reduced with respect to other available models. We discuss line shapes for such disks and present a code for modelling observational data with this scheme in X-ray data analysis programs. A detailed discussion will soon be presented in a forthcoming paper (Dauser et al. 2010).

Radio spectra, observed during solar flares, are usually very complex (many bursts and fine structures). We have developed a new method to separate them into individual bursts and analyze them separately. The method is used in the analysis of the 0.8–2.0 GHz radio spectrum of the April 11, 2001 event, which was rich in drifting pulsating structures (DPSs). Using this method we showed that the complex radio spectrum consists of at least four DPSs separated with respect to their different frequency drifts (−115, −36, −23, and −11 MHz s−1). These DPSs indicate a presence of at least four plasmoids expected to be formed in a flaring current sheet. These plasmoids produce the radio emission on close frequencies giving thus a mixture of superimposed DPSs observed in the radio spectrum.

Radio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

We present a lepto-hadronic model for the VHE emission from the relativistic jets of FR I radiogalaxies. We assume that protons and electrons are accelerated in a compact region near the base of the jet, and they cool emitting multiwavelength radiation as they propagate along the jet. The particle distributions are obtained using an inhomogeneous steady-state transport equation that accounts for the cooling processes as well as the convection of particles in the jet. The dominant processes that contribute to the photon SED are electron and proton synchrotron radiation, inverse Compton interactions, and the inelastic collisions pp and pγ. The accompanying neutrino output is obtained and the possibility of detection with Km3Net and IceCube is discussed for the cases of Cen A and M87.

A self-consistent nonlinear dynamo model is presented. The nonlinear behavior of the plasma at small scale is described by using a MHD shell model for fields fluctuations; this allow us to study the dynamo problem in a large parameter regime which characterizes the dynamo phenomenon in many natural systems and which is beyond the power of supercomputers at today. The model is able to reproduce dynamical situations in which the system can undergo transactions to different dynamo regimes. In one of these the large-scale magnetic field jumps between two states reproducing the magnetic polarity reversals. From the analysis of long time series of reversals we infer results about the statistics of persistence times, revealing the presence of hidden long-time correlations in the chaotic dynamo process.

Systems of two very different sizescales are known to produce very high-energy (VHE) radiation in their jets: AGNs and microquasars. The produced VHE photons (Eγ ~ 1 TeV) can be absorbed by the intense environmental soft photon fields, coming from the companion star (in high mass binaries) or from the accreting material (disk+corona in AGNs), as these are the dominant sources at energies around ~(mec2)2/Eγ. Energetic pairs are created by the photon-photon annihilation, and, depending on how efficient are the competing cooling channels, the absorption can lead to a reprocessing by Inverse Compton pair-cascade development. A self-consistent modeling of these systems as gamma-ray sources should then include, along with the emission and absorption processes, a thorough treatment of the pair cascades. We discuss here on this issue, focusing on our (preliminary) results of numerical simulations devoted to a study case similar to the high-mass microquasar candidate LS 5039.

The standard magnetohydrodynamic (MHD) description of the plasma in the hot, magnetized gas of the intra-cluster (ICM) medium is not adequate because it is weakly collisional. In such collisionless magnetized gas, the microscopic velocity distribution of the particles is not isotropic, giving rise to kinetic effects on the dynamical scales. These kinetic effects could be important in understanding the turbulence as well as the amplification and maintenance of the magnetic fields in the ICM. It is possible to formulate fluid models for collisonless or weakly collisional gas by introducing modifications in the MHD equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD model based on the CGL-closure, which allows the adiabatic evolution of the two components of the pressure tensor (the parallel and perpendicular components with respect to the local magnetic field), we performed 3D numerical simulations of forced turbulence in order to study the amplification of an initially weak seed magnetic field. We found that the growth rate of the magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but the magnetic energy saturates in a level smaller than that of the MHD case. We also found that a necessary condition for the dynamo to operate is to impose constraints on the anisotropy of the pressure.

We present new insights about accretion and ejection physics based on joint RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the first time, with fast phase-resolved spectroscopy of the ρ state, we are able to show that changes in the broadband X-ray spectrum (RXTE) on timescales of seconds are associated with measurable changes in absorption lines (Chandra HETGS) from the accretion disk wind. Additionally, we make a direct detection of material evaporating from the radiation-pressure-dominated inner disk. Our X-ray data thus reveal the black hole as it ejects a portion of the inner accretion flow and then drives a wind from the outer disk, all in a bizarre cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that the accretion disk wind may be sufficiently massive to play an active role in GRS 1915+105, not only in quenching the jet on long timescales, but also in possibly producing or facilitating transitions between classes of X-ray variability.

The spatio-temporal dynamics of the solar magnetic field has been investigated by using NSO/Kitt Peak synoptic magnetic maps covering ~28 yr. For each heliographic latitude the field has been analyzed through the Empirical Mode Decomposition, in order to investigate the time evolution of the various characteristic oscillating frequencies. Preliminary results are discussed.

Over the 18 years since its discovery, GRS 1915+105 has continuously brightened in the X/γ-ray sky. It is considered the prototypical microquasar. Most of these are LMXBs that show sporadic ejection of matter at apparently superluminal velocities. In these the three basic ingredients of quasars are found: a black hole, an accretion disc and collimated jets of high energy particles, but in microquasars the black hole is only a few M⊙ instead of several × 106 M⊙; the accretion disc had mean thermal temperature of several × 106 K instead of several × 103 K, and the particles ejected at relativistic speeds travel distances of a few ly only, compared to few × 106 ly as in radio galaxies. However many open issues remain to be addressed.

We have begun a series of laboratory experiments focused on understanding how coronal mass ejections (CME) interact and evolve in the solar wind. The experiments make use of the Helicon-Cathode (HelCat) plasma facility, and the Plasma Bubble eXperiment (PBeX). PBeX can generate CME-like structures (sphereomak geometry) that propagate into the high-density, magnetized background plasma of the HelCat device. The goal of the current research is to compare CME evolution under conditions where there is sheared flow in the background plasma, versus without flow; observations suggest that CME evolution is strongly influenced by such sheared flow regions. Results of these studies will be used to validate numerical simulations of CME evolution, in particular the 3D BATS-R-US MHD code of the University of Michigan. Initial studies have characterized the plasma bubble as it evolves into the background field with and without plasma (no shear).

This paper reports the discovery and presents the results of a first analysis of the observed morphology of a candidate external irradiated circumstellar disk/jet system found in the deep core of Trumpler 14, a cluster an order of magnitude more massive than the only cluster where bona-fide proplyds have been found, the Trapezium cluster in the Orion Nebula.

We obtained the first spectral predictions from a simulation of the Galactic Center to include radiative processes internally. We performed simulations with and without cooling, with and without spin, and for different initial configurations of the magnetic field, in order to test the effect on jet launching and inner accretion disk characteristics. By exploring parameter space, we will attempt to place new constraints on the controversial question about the presence or not of a jet from Sgr A*, as well as study jet launching in general. We have shown that, as expected, the spin of the BH affects the structure of the jet. The presence of cooling also strongly influences the inner structure of the accretion disk and therefore affects jet launching. These results show that radiative cooling is not negligible, as is usually assumed for the very underluminous supermassive BH, Sgr A*. On the contrary, the inclusion of cooling has a very visible influence on the accretion disk. Furthermore it creates an important difference in the resulting spectra.

We show one of possible directions of general relativistic MHD (GRMHD) calculations of astrophysical relativistic jet formation. This was motivated by observations of radio knot ejections associated with high energy flares of an AGN in M87 and micro-quasars. We introduce a modified version of a solar flare model for the phenomenon. In the model, we have to consider a process beyond the ideal GRMHD. Especially, we focus on the special features of general relativistic plasmas around rotating black holes.

Blazars are radio-loud active galactic nuclei (AGN) dominated by relativistic jets seen at small angles to the line-of-sight. They exhibit dramatic flux variations across the electromagnetic spectrum. The fastest variations are observed in the X-ray and γ-ray bands on time-scales of hours or even minutes. Currently, a substantial part of the blazar literature has been based on the study of these temporal variations through the use of structure function (SF) analysis, the results of which are believed to put great constrains on the jet-physics.

The SF is often invoked in the framework of shot-noise models to determine the temporal properties of individual shots within the jet as well as their geometrical sizes. We argue, that for blazar variability studies, the SF-results are sometimes erroneously interpreted leading to misconceptions about the actual source properties. Based on extensive simulations we caution that spurious breaks will appear in the SFs of almost all light-curves, even though these light-curves may contain no intrinsic characteristic time-scale.

Finally, it is also commonly thought that SFs are immune to the sampling problems, such as data-gaps, which affects the estimators of the underlying power spectra density function such as the periodogram. However, we show that SFs are also troubled by gaps which can induce artefacts.

We present an extension of the Unno-Rachkovsky solution that provides the theoretical profiles coming out of a Milne-Eddington atmosphere imbedded in a magnetic field, to the additional taking into account of a vertical velocity gradient. Thus, the theoretical profiles may display asymmetries as do the observed profiles, which facilitates the inversion based on the Unno-Rachkovsky theory, and leads to the additional determination of the vertical velocity gradient. We present UNNOFIT inversion on spectropolarimetric data performed on an active region of the Sun with the french-italian telescope THEMIS operated by CNRS and CNR on the island of Tenerife.

Both types of long and short gamma ray bursts involve a stage of a hyper-Eddington accretion of hot and dense plasma torus onto a newly born black hole. The prompt gamma ray emission originates in jets at some distance from this ‘central engine’ and in most events is rapidly variable, having a form of sipkes and subpulses. This indicates at the variable nature of the engine itself, for which a plausible mechanism is an internal instability in the accreting flow. We solve numerically the structure and evolution of the neutrino-cooled torus. We take into account the detailed treatment of the microphysics in the nuclear equation of state that includes the neutrino trapping effect. The models are calculated for both Schwarzschild and Kerr black holes. We find that for sufficiently large accretion rates (>~10M⊙ s−1 for non-rotating black hole, and >~1M⊙ s−1 for rotating black hole, depending on its spin), the inner regions of the disk become opaque, while the helium nuclei are being photodissociated. The sudden change of pressure in this region leads to the development of a viscous and thermal instability, and the neutrino pressure acts similarly to the radiation pressure in sub-Eddington disks. In the case of rapidly rotating black holes, the instability is enhanced and appears for much lower accretion rates. We also find the important and possibly further destabilizing role of the energy transfer from the rotating black hole to the torus via the magnetic coupling.