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Polarization and wavelength are the bits of information attached to every photon that reveal the most about its formation and subsequent history. The E-ELT will, for the foreseeable future, be the most powerful optical light-collecting machine ever built. The strength of its combination, spectropolarimetry with the E-ELT, is the anchorage in physics of astronomical observations. I present a strawman design of a spectropolarimeter for its intermediate focus.
We study the global evolution of the magnetic field and interstellar medium (ISM) of the barred and ringed galaxies in the presence of non-axisymmetric components of the potential, i.e. the bar and/or the oval perturbations. The magnetohydrodynamical dynamo is driven by cosmic rays (CR), which are continuously supplied to the disk by supernova (SN) remnants. Additionally, weak, dipolar and randomly oriented magnetic field is injected to the galactic disk during SN explosions. To compare our results directly with the observed properties of galaxies we construct realistic maps of high-frequency polarized radio emission. The main result is that CR driven dynamo can amplify weak magnetic fields up to few μG within few Gyr in barred and ringed galaxies. What is more, the modelled magnetic field configuration resembles maps of the polarized intensity observed in barred and ringed galaxies.
Relationships between the X-ray and radio behavior of black hole X-ray binaries during outbursts have established a fundamental coupling between the accretion disks and radio jets in these systems. I begin by reviewing the prevailing paradigm for this disk-jet coupling, also highlighting what we know about similarities and differences with neutron star and white dwarf binaries. Until recently, this paradigm had not been directly tested with dedicated high-angular resolution radio imaging over entire outbursts. Moreover, such high-resolution monitoring campaigns had not previously targetted outbursts in which the compact object was either a neutron star or a white dwarf. To address this issue, we have embarked on the Jet Acceleration and Collimation Probe Of Transient X-Ray Binaries (JACPOT XRB) project, which aims to use high angular resolution observations to compare disk-jet coupling across the stellar mass scale, with the goal of probing the importance of the depth of the gravitational potential well, the stellar surface and the stellar magnetic field, on jet formation. Our team has recently concluded its first monitoring series, including (E)VLA, VLBA, X-ray, optical, and near-infrared observations of entire outbursts of the black hole candidate H 1743-322, the neutron star system Aquila X-1, and the white dwarf system SS Cyg. Here I present preliminary results from this work, largely confirming the current paradigm, but highlighting some intriguing new behavior, and suggesting a possible difference in the jet formation process between neutron star and black hole systems.
In recent analyses of numerical simulation and solar wind dataset, the idea that the magnetic discontinuities may be related to intermittent structures that appear spontaneously in MHD turbulence has been explored in details. These studies are consistent with the hypothesis that discontinuity events founds in the solar wind might be of local origin as well, i.e. a by-product of the turbulent evolution of magnetic fluctuations.
Using simulations of 2D MHD turbulence, we are exploring a possible link between tangential discontinuities and magnetic reconnection. The goal is to develop numerical algorithms that may be useful for solar wind applications.
A characteristic feature of fluid theories concerns the difficulty of uniquely defining consistent closure conditions for the fluid equations. In fact it is well known that fluid theories cannot generally provide a closed system of equations for the fluid fields. This feature is typical of collisionless plasmas where, in contrast to collisional plasmas, asymptotic closure conditions do not follow as a consequence of an H-theorem This issue is of particular relevance in astrophysics where fluid approaches are usually adopted. On the other hand, it is well known that the determination of the closure conditions is in principle achievable in the context of kinetic theory. In the case of multi-species thermal magnetoplasmas this requires the determination of the species tensor pressure and of the corresponding heat fluxes. In this paper we investigate this problem in the framework of the Vlasov-Maxwell description for collisionless axisymmetric magnetoplasmas arising in astrophysics, with particular reference to accretion discs around compact objects (like black holes and neutron stars). The dynamics of collisionless plasmas in these environments is determined by the simultaneous presence of gravitational and magnetic fields, where the latter may be both externally produced and self-generated by the plasma currents. Our starting point here is the construction of a solution for the stationary distribution function describing slowly-varying gyrokinetic equilibria. The treatment is applicable to non-relativistic axisymmetric systems characterized by temperature anisotropy and differential rotation flows. It is shown that the kinetic formalism allows one to solve the closure problem and to consistently compute the relevant fluid fields with the inclusion of finite Larmor-radius effects. The main features of the theory and relevant applications are discussed.
Using 3D-MHD Eulerian-grid numerical simulations, we study the formation and evolution of rising magnetic towers propagating into an ambient medium. The towers are generated from a localized injection of pure magnetic energy. No rotation is imposed on the plasma. We compare the evolution of a radiatively cooling tower with an adiabatic one, and find that both bend due to pinch instabilities. Collimation is stronger in the radiative cooling case; the adiabatic tower tends to expand radially. Structural similarities are found between these towers and the millimeter scale magnetic towers produced in laboratory experiments.
We review the present results on the study of the propagation of relativistic collimated outflows characteristics of active galaxies and active stars. Magnetic fields, namely their azimuthal components, gives rise to current driven instabilities whose nonlinear development can actually be connected to the complex morphologies observed in astrophysical jets.
Correlations between the radio and X-ray bands in the hard state of black hole X-ray binaries (BHBs) have led to the discovery of the Fundamental Plane of black hole accretion, linking accretion-driven radiative attributes to black hole mass. Although this discovery has led to new constraints on radiative efficiencies, there is still significant degeneracy in terms of understanding the governing physics. I present several new results exploring the processes driving the Fundamental Plane over the black hole mass range. These include the first ever homogeneous fits of sources at approximately the same Eddington luminosity but millions of times different in mass, which I focus on for this proceeding article.
By making use of the MHD self-induction equation in general relativity (GR), recently derived by Clarkson and Marklund (2005), it is shown that when Friedmann universe possesses a spatial section whose Riemannian curvature is negative, the magnetic energy bounds computed by Nuñez (2002) also bounds the growth rate of the magnetic field given by the strain matrix of dynamo flow. Since in GR-MHD dynamo equation, the Ricci tensor couples with the universe magnetic field, only through diffusion, and most ages are highly conductive the interest is more theoretical here, and only very specific plasma astrophysical problems can be address such as in laboratory plasmas. Magnetic fields and the negative curvature of some isotropic cosmologies, contribute to enhence the amplification of the magnetic field. Ricci curvature energy is shown to add to strain matrix of the flow, to enhance dynamo action in the universe. Magnetic fluctuations of the Clarkson-Marklund equations for a constant magnetic field seed in highly conductive flat universes, leads to a magnetic contrast of ≈ 2, which is well within observational limits from extragalactic radiosources of ≈ 1.7. In the magnetic helicity fluctuations the magnetic contrast shows that the dynamo effects can be driven by these fluctuations.
We present discovery of a radio nebula associated with the ultraluminous X-ray source (ULX) IC 342 X-1 using the Very Large Array (VLA). Taking the surrounding nebula as a calorimeter, one can constrain the intrinsic power of the ULX source. We compare the obtained power that is needed to supply the radio nebula with the W50 nebula powered by the microquasar SS433 and with other ULXs. We find that the power required is at least two orders of magnitude greater than that needed to power radio emission from the W50 nebula associated with the microquasar SS433. In addition, we report the detection of a compact radio core at the location of the X-ray source.
We present a new model of emission from jets in microquasars, which implements elements from the study of jets in gamma-ray bursts to these objects. By assuming that electrons are accelerated once at the base of the jet to a power law distribution above a low energy Maxwellian, and are cooled by synchrotron emission and possible adiabatic energy losses along the jet, a wealth of spectra can be obtained. We show our theoretical results which can explain some of the key observations. In particular, we show that: (I) a flat radio spectrum, as is frequently seen, is a natural outcome of the model; (II) Strong magnetic field results in a flux decay in the optical/UV band as Fν ~ ν−1/2, irrespective of many of the uncertainties of the model. (III) An increase of the magnetic field above a critical value of ~105 G leads to a sharp decrease in the flux at the radio band, while the flux at higher frequencies saturates to a constant value. We conclude that scatter in the values of the magnetic field may provide a natural explanation to the observed scatter in the radio/X ray luminosity correlation seen in these objects.
We describe a CME event, occurred in NOAA 11059 on April 3 2010, using STEREO and MDI/SOHO data. We analyze the CME evolution using data provided by SECCHI-EUVI and COR1 onboard STEREO satellites, and we perform a 3D reconstruction of the CME using the LCT-TP method. Using MDI/SOHO line-of-sight magnetograms we analyze the magnetic configuration of NOAA 11059 and we determine the magnetic helicity trend.
The theory of strong MHD turbulence with cross-helicity has been a subject of many recent studies. In this paper we focused our attention on low-imbalance limit and performed high-resolution 3D simulations. The results suggest that in this limit both w+=v+b and w−=v−b are cascaded strongly. The model for imbalance based on so-called “dynamic alignment” strongly contradicts numerical evidence.
Understanding the variable emission of blazars observed with gamma-ray telescopes and Fermi has become a major challenge for theoretical models of particle acceleration. Here, we introduce a novel time-dependent emission model in which the maximum energy of particles is determined from a balance between Fermi type I and II acceleration energy gains and radiative energy losses, allowing for an explanation of both the characteristic spectral energy distribution of blazars and their intrinsic sub-hour variability. Additionally, we can determine the physical condition of the emitting plasma concerning its turbulence and typical shock speeds.
The recent years witnessed a dramatic improvement in our knowledge of the phenomenology and physics of Gamma Ray Bursts (GRBs). However, our “pillars of knowledge” remain a few, while many aspects remain obscure and not understood. There is no general agreement on the radiation mechanism of the prompt emission, nor on the process able to convert the bulk motion of the fireball into random energy of the emitting leptons. The afterglow phase can now be studied at very early phases, showing an unforeseen phenomenology, still to be understood. In this context, the detection of ~GeV emission from ~10% of GRBs, made possible by the Fermi satellite, can hopefully shed light on some controversial issues.
In this study, we present the results from 3D simulations in which a side-streaming motion pushes the post-bow shock into direct contact with the jet beam. This is a possible mechanism for modeling well collimated molecular jets as an atomic/ionic flow which entrains molecules initially present only in the surrounding environment.
It is pointed out that the standard model for pulsar electrodynamics is based on a false premise, related to neglecting the displacement current, and the associated need for current screening. Wave dispersion in the standard model is reviewed, and its relation to the interpretation of pulsar radio emission and its polarization is discussed. Inclusion of the displacement current results in large-amplitude oscillations; some of the implications of these oscillations on the interpretation of the radio emission are discussed.
The 16m quasar 3C 345 is one of the best examples of an AGN showing structural and flux variability on parsec scales around a compact unresolved radio core. It has been observed from radio to γ-ray wavebands with a special focus on Very Long Baseline Interferometry (VLBI) observations in the range 1-100 GHz that cover a period of over 30 years. The complex pc-scale jet of 3C 345 exemplifies an archetypal “superluminal” jet with helical substructure. Existing VLBI observations of 3C 345 form an unprecedented database enabling a unique insight into the long-term evolution of the pc-scale radio emission. Here we present the latest results from our ongoing long-term VLBI monitoring of 3C 345, focusing on the morphological, kinematic, and spectral evolution of the pc-scale jet. Special attention will be given to the recent onset of a new period of high activity in the source that has been manifesting itself since 2008 from radio through γ-rays. Recent VLBI and high energy observations to study the relation between the radio emission and the production of high energy photons in 3C 345 are combined.
Discovery of soft X-ray radiation from comet Hyakutake C/1996 B2 by space telescope ROSAT in March 1996 as well as establishing the regularity of the phenomenon for comets in general opened a new area of research for the plasma astrophysics. The first soft X-ray observations have been motivated by the results of a theoretical investigation on the efficiency of production of energetic photons, in the energy range 0.1-1 keV, by hot plasma clumps generated in dusty comets via high velocity collision with interplanetary dust at small heliocentric distances. Moreover, the soft X-ray luminosities measured significantly exceeded the value predicted. A short review of proposed theoretical models and mechanisms for explaining X-ray emission from comets as well as some prospects for the future X ray observations of comets are presented.
The origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We observed M87 with PACS and SPIRE as part of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data with a synchrotron model based on infrared, submm and radio data to investigate the origin of the far-infrared emission. We find that both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87.