Energy spectrum, dissipation and spatial structures in reduced Hall magnetohydrodynamic

We analyze the effect of the Hall term in the magnetohydrodynamic turbulence under a strong externally supported magnetic field, seeing how this changes the energy cascade, the characteristic scales of the flow and the dynamics of global magnitudes, with particular interest in the dissipation. Numerical simulations of freely evolving three-dimensional reduced magnetohydrodynamics (RHMHD) are performed, for different values of the Hall parameter (the ratio of the ion skin depth to the macroscopic scale of the turbulence) controlling the impact of the Hall term. The Hall effect modifies the transfer of energy across scales, slowing down the transfer of energy from the large scales up to the Hall scale (ion skin depth) and carrying faster the energy from the Hall scale to smaller scales. The final outcome is an effective shift of the dissipation scale to larger scales but also a development of smaller scales. Current sheets (fundamental structures for energy dissipation) are affected in two ways by increasing the Hall effect, with a widening but at the same time generating an internal structure within them. In the case where the Hall term is sufficiently intense, the current sheet is fully delocalized. The effect appears to reduce impulsive effects in the flow, making it less intermittent.Comment: 17 pages, 10 figure

Modeling the variability of the BL Lacertae object PKS 2155-304

The bright X-ray selected BL Lacertae object PKS 2155-304 has been the target of two intense multiwavelength campaigns, in November 1991 and in May 1994. Although the spectral energy distributions at both epochs were quite similar, the source exhibited two very distinct variability patterns that cannot be easily reconciled with homogeneous, one-zone jet models. During the first epoch the variability was almost achromatic in amplitude, with a time lag between X-rays and UV of $\approx 3$ h, while during the second epoch the variability amplitude increased as a function of wavelength, with the EUV flare peaking $\approx 1$ day after the X-ray flare. We model the source using a time-dependent inhomogeneous accelerating jet model. e reproduce the general characteristics of the different variability signatures by assuming that plasma disturbances with different physical properties propagate downstream in an underlying jet characterized by the same set of physical parameters at both epochs. A time delay of $\approx$ 1 day between the hardening of the UV spectral index and the UV flux, present at both epochs, is modeled with stochastic fluctuations in the particle acceleration manifested through small variations of the maximum energy of the injected electrons. We predict that similar time delays will be present in future observations, even in the absence of strong variability events. We stress the importance of observations at neighboring frequencies as a diagnostic tool for the structure of the quiescent jet in blazars, especially in the seemingly dull case when strong variability is absent.Comment: 8 pages, 5 figures. Accepted in ApJ Letter

Pilot3 D7.1 - Dissemination, communication and exploitation plan

This document is the Communication, Dissemination and Exploitation Plan (D7.1) of the Clean Sky 2 Innovation Action Pilot3. The document defines the communication and dissemination actions to be performed during the project, and the potential exploitation of the project results. A complete strategy of communication is presented, as well as the items and content already prepared for it

Ferromagnetic 0-pi Junctions as Classical Spins

The ground state of highly damped PdNi based 0-pi ferromagnetic Josephson junctions shows a spontaneous half quantum vortex, sustained by a supercurrent of undetermined sign. This supercurrent flows in the electrode of a Josephson junction used as a detector and produces a phi(0)/4 shift in its magnetic diffraction pattern. We have measured the statistics of the positive or negative sign shift occurring at the superconducting transition of such a junction. The randomness of the shift sign, the reproducibility of its magnitude and the possibility of achieving exact flux compensation upon field cooling: all these features show that 0-pi junctions behave as classical spins, just as magnetic nanoparticles with uniaxial anisotropy.Comment: 4 pages, 4 figure

Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345

We investigate whether a pc-scale jet of 3C345 is dominated by a normal plasma or an electron-positron plasma. We present a general condition that a jet component becomes optically thick for synchrotron self-absorption, by extending the method originally developed by Reynolds et al. The general condition gives a lower limit of the electron number density, with the aid of the surface brightness condition, which enables us to compute the magnetic field density. Comparing the lower limit with another independent constraint for the electron density that is deduced from the kinetic luminosity, we can distinguish the matter content. We apply the procedure to the five components of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes at the peak frequencies were obtainable from literature. Evaluating the representative values of Doppler beaming factors by their equipartition values, we find that all the five components are likely dominated by an electron-positron plasma. The conclusion does not depend on the lower cutoff energy of the power-law distribution of radiating particles.Comment: 17 page

Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate

We observe coherent spin oscillations in an antiferromagnetic spin-1 Bose-Einstein condensate of sodium. The variation of the spin oscillations with magnetic field shows a clear signature of nonlinearity, in agreement with theory, which also predicts anharmonic oscillations near a critical magnetic field. Measurements of the magnetic phase diagram agree with predictions made in the approximation of a single spatial mode. The oscillation period yields the best measurement to date of the sodium spin-dependent interaction coefficient, determining that the difference between the sodium spin-dependent s-wave scattering lengths $a_{f=2}-a_{f=0}$ is $2.47\pm0.27$ Bohr radii.Comment: 5 pages, 2 figures. Changes: added reference, minor correction

The Origin of Complex Behavior of Linearly Polarized Components in Parsec-Scale Jets

Evidence that the magnetic fields of extragalactic jets have a significant fraction of their energy in a random component is briefly summarized, and a detailed model of evolving, jet polarization structures is constructed, based on this picture. The evolving magnetic field structure of an oblique shock complex that forms in a relativistic jet simulation is explored by using velocity data from the hydrodynamical simulation to advect an initially random magnetic field distribution. Radiative transfer calculations reveal that emission from a propagating region of magnetic field, `ordered' by the shock, and lying approximately transverse to the flow direction, merges with that from an evolving sheared region at the flow periphery. If such a flow were barely resolved, observation would suggest evolution from a somewhat oblique, to a more longitudinal, magnetic field structure with respect to the flow axis, while higher resolution observations would infer a component following a non-linear trajectory, and with a magnetic field orientation that rotates during evolution. This result highlights the ambiguity in interpreting VLBP data, and illustrates the importance of simulations in providing a framework for proper interpretation of such data.Comment: Accepted for publication in ApJ (Part I). Low res. figures; originals may be obtained from the "Relativistic Flows" section of http://www.astro.lsa.umich.edu/users/hughes

Dispatcher3 D7.1 - Project communication, dissemination and exploitation plan

This document is the Communication, Dissemination and Exploitation Plan (D7.1) of the Clean Sky 2 Innovation Action Dispatcher3. The document defines the communication and dissemination actions to be performed during the project, and the potential exploitation of the project results. A complete strategy of communication is presented, as well as the items and content already prepared for it