Interpreting the time variable RM observed in the core region of the TeV blazar Mrk 421

In this work we interpret and discuss the time variable rotation measure (RM) found, for the first time over a 1-yr period, in the core region of a blazar. These results are based on a one-year, multi-frequency (15, 24, and 43 GHz) Very Long Baseline Array (VLBA) monitoring of the TeV blazar Markarian 421 (Mrk 421). We investigate the Faraday screen properties and its location with respect to the jet emitting region. Given that the 43 GHz radio core flux density and the RM time evolution suggest a similar trend, we explore the possible connection between the RM and the accretion rate. Among the various scenarios that we explore, the jet sheath is the most promising candidate for being the main source of Faraday rotation. During the one-year observing period the RM trend shows two sign reversals, which may be qualitatively interpreted within the context of the magnetic tower models. We invoke the presence of two nested helical magnetic fields in the relativistic jet with opposite helicities, whose relative contribution produce the observed RM values. The inner helical field has the poloidal component ($B_{\rm p}$) oriented in the observer's direction and produces a positive RM, while the outer helical field, with $B_{\rm p}$ in the opposite direction, produces a negative RM. We assume that the external helical field dominates the contribution to the observed RM, while the internal helical field dominates when a jet perturbation arises during the second observing epoch. Being the intrinsic polarization angle parallel to the jet axis, a pitch angle of the helical magnetic field $\phi\gtrsim 70^\circ$ is required. Additional scenarios are also considered to explain the observed RM sign reversals.Comment: 6 pages, 2 figures. Published on MNRA

Investigating the Effects of Finite Resolution on Observed Transverse Jet Profiles

Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic fields that thread them. Faraday Rotation gradients are a very important way of investigating these magnetic fields, and can provide information on the orientation and structure of the magnetic field in the immediate vicinity of the jet; for example, a toroidal or helical field component should give rise to a systematic gradient in the observed Faraday rotation across the jet, as well as characteristic intensity and polarization profiles. However, real observed radio images have finite resolution, usually expressed via convolution with a Gaussian beam whose size corresponds to the central lobe of the point source response function. This will tend to blur transverse structure in the jet profile, raising the question of how well resolved a jet must be in the transverse direction in order to reliably detect transverse structure associated with a helical jet magnetic field. We present results of simulated intensity, polarization and Faraday rotation images designed to directly and empirically investigate the effect of finite resolution on observed transverse jet structures

Multifrequency Polarimetry of the Nrao 140 Jet: Possible Detection of a Helical Magnetic Field and Constraints on its Pitch Angle

We present results from multifrequency polarimetry of NRAO 140 using the Very Long Baseline Array. These observations allow us to reveal the distributions of both the polarization position angle and the Faraday rotation measure (RM). These distributions are powerful tools to discern the projected and line-of-sight components of the magnetic field, respectively. We find a systematic gradient in the RM distribution, with its sign being opposite at either side of the jet with respect to the jet axis. The sign of the RM changes only with the direction of the magnetic field component along the line of sight, so this can be explained by the existence of helical magnetic components associated with the jet itself. We derive two constraints for the pitch angle of the helical magnetic field from the distributions of the RM and the projected magnetic field; the RM distribution indicates that the helical fields are tightly wound, while that of the projected magnetic field suggests they are loosely wound around the jet axis. This inconsistency may be explained if the Faraday rotator is not cospatial with theemitting region. Our results may point toward a physical picture in which an ultra-relativistic jet (spine) with a loosely wound helical magnetic field is surrounded by a sub-relativistic wind layer (sheath) with a tightly wound helical magnetic field.Comment: 12 pages, 4 figures, ApJ, in pres

Gravitational wave forms for a three-body system in Lagrange's orbit: parameter determinations and a binary source test

Continuing work initiated in an earlier publication [Torigoe et al. Phys. Rev. Lett. {\bf 102}, 251101 (2009)], gravitational wave forms for a three-body system in Lagrange's orbit are considered especially in an analytic method. First, we derive an expression of the three-body wave forms at the mass quadrupole, octupole and current quadrupole orders. By using the expressions, we solve a gravitational-wave {\it inverse} problem of determining the source parameters to this particular configuration (three masses, a distance of the source to an observer, and the orbital inclination angle to the line of sight) through observations of the gravitational wave forms alone. For this purpose, the chirp mass to a three-body system in the particular configuration is expressed in terms of only the mass ratios by deleting initial angle positions. We discuss also whether and how a binary source can be distinguished from a three-body system in Lagrange's orbit or others.Comment: 21 pages, 3 figures, 1 table; text improved, typos corrected; accepted for publication in PR

Fluctuations of the Lyapunov exponent in 2D disordered systems

We report a numerical investigation of the fluctuations of the Lyapunov exponent of a two dimensional non-interacting disordered system. While the ratio of the mean to the variance of the Lyapunov exponent is not constant, as it is in one dimension, its variation is consistent with the single parameter scaling hypothesis

Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction

The intriguing nano-structural properties of a ZnMnGaO4 film epitaxially grown on MgO (001) substrate have been investigated using synchrotron radiation-based x-ray diffraction. The ZnMnGaO4 film consisted of a self-assembled checkerboard (CB) structure with perfectly aligned and regularly spaced vertical nanorods. The lattice parameters of the orthorhombic and rotated tetragonal phases of the CB structure were analyzed using H-K, H-L, and K-L cross sections of the reciprocal space maps measured around various symmetric and asymmetric reflections of the spinel structure. We demonstrate that the symmetry of atomic displacements at the phases boundaries provides the means for coherent coexistence of two domains types within the volume of the film

Conductance of nano-systems with interactions coupled via conduction electrons: Effect of indirect exchange interactions

A nano-system in which electrons interact and in contact with Fermi leads gives rise to an effective one-body scattering which depends on the presence of other scatterers in the attached leads. This non local effect is a pure many-body effect that one neglects when one takes non interacting models for describing quantum transport. This enhances the non-local character of the quantum conductance by exchange interactions of a type similar to the RKKY-interaction between local magnetic moments. A theoretical study of this effect is given assuming the Hartree-Fock approximation for spinless fermions in an infinite chain embedding two scatterers separated by a segment of length L\_c. The fermions interact only inside the two scatterers. The dependence of one scatterer onto the other exhibits oscillations which decay as 1/L\_c and which are suppressed when L\_c exceeds the thermal length L\_T. The Hartree-Fock results are compared with exact numerical results obtained with the embedding method and the DMRG algorithm

Anderson transition in the three dimensional symplectic universality class

We study the Anderson transition in the SU(2) model and the Ando model. We report a new precise estimate of the critical exponent for the symplectic universality class of the Anderson transition. We also report numerical estimation of the $\beta$ function.Comment: 4 pages, 5 figure

Choreographic solution to the general relativistic three-body problem

We revisit the three-body problem in the framework of general relativity. The Newtonian N-body problem admits choreographic solutions, where a solution is called choreographic if every massive particles move periodically in a single closed orbit. One is a stable figure-eight orbit for a three-body system, which was found first by Moore (1993) and re-discovered with its existence proof by Chenciner and Montgomery (2000). In general relativity, however, the periastron shift prohibits a binary system from orbiting in a single closed curve. Therefore, it is unclear whether general relativistic effects admit a choreographic solution such as the figure eight. We carefully examine general relativistic corrections to initial conditions so that an orbit for a three-body system can be closed and a figure eight. This solution is still choreographic. This illustration suggests that the general relativistic N-body problem also may admit a certain class of choreographic solutions.Comment: 10 pages, 4 figures, text improved, accepted for publication in PR