B2 1144+35B, a giant low power radio galaxy with superluminal motion. Orientation and evidence for recurrent activity

The goal of this work is a detailed study of the nearby, low power radio galaxy B2 1144+35B. For this purpose, we performed new Very Long Baseline Array (VLBA) and Very Large Array (VLA) observations. This source has several properties (bright, nearby, large range of spatial structures, visible counterjet, etc.) that make it an excellent astrophysical laboratory for the study of the evolution of radio jets. Here we report the detection of motion in the counterjet at 0.23 $\pm$ 0.07 c, which allows us to estimate the orientation of the parsec-scale jet at 33$^\circ \pm 7^\circ$ from the line of sight, with an intrinsic velocity of (0.94$^{+0.06}_{-0.11}$)c. We also report on a brightening of the core at high frequencies which we suggest could be the result of a new component emerging from the core. High dynamic range VLBA observations at 5 GHz reveal, for the first time, extended emission connecting the core with the bright complex of emission that dominates the flux density of the parsec scale structure at frequencies below 20 GHz. The evolution of this bright complex is considered and its slow decline in flux density is interpreted as the result of an interaction with the interstellar medium of the host galaxy.Comment: 7 pages, 6 b&w figures. A&A in pres

Dynamical suppression of non-adiabatic modes

Recent analyses of the WMAP 5-year data constrain possible non-adiabatic contributions to the initial conditions of CMB anisotropies. Depending upon the early dynamics of the plasma, the amplitude of the entropic modes can experience a different suppression by the time of photon decoupling. Explicit examples of the latter observation are presented both analytically and numerically when the post-inflationary dynamics is dominated by a stiff contribution.Comment: 9 pages, four figure

Gorkov equations for a pseudo-gapped high temperature superconductor

A theory of superconductivity based on the two-body Cooperon propagator is presented. This theory takes the form of a modified Gorkov equation for the Green's function and allows one to model the effect of local superconducting correlations and long range phase fluctuations on the spectral properties of high temperature superconductors, both above and below Tc. A model is proposed for the Cooperon propagator, which provides a simple physical picture of the pseudo-gap phenomenon, as well as new insights into the doping dependence of the spectral properties. Numerical calculations of the density of states and spectral functions based on this model are also presented, and compared with the experimental STM and ARPES data. It is found, in particular, that the sharpness of the peaks in the density of states is related to the strength and the range of the superconducting correlations and that the apparent pseudo-gap in STM and ARPES can be different, although the underlying model is the same.Comment: REVTEX 3.1, 8 pages, 5 EPS figures, submitted to Phys. Rev.

High resolution imaging of the radio continuum and neutral gas in the inner kiloparsec of the radio galaxy 3C293

Using a combination of observations involving the VLA, MERLIN and global VLBI networks we have made a detailed study of the radio continuum and the neutral hydrogen (HI) kinematics and distribution within the central kiloparsec of the radio galaxy 3C293. These observations trace the complex jet structure and identify the position of the steeply inverted radio core at 1.3GHz. Strong HI absorption is detected against the majority of the inner kiloparsec of 3C293. This absorption is separated into two dynamically different and spatially resolved systems. Against the eastern part of the inner radio jet narrow HI absorption is detected and shown to have higher optical depths in areas co-spatial with a central dust lane. Against the western jet emission and core component, broad and complex HI absorption is detected. This broad and complex absorption structure is discussed in terms of two possible interpretations for the gas kinematics observed: that the gas is situated in two gas layers or that it is in a sub-kiloparsec disk rotating about the core. (Abridged)Comment: 14 pages, 8 figures, To be published in MNRAS. High resolution version is available at http://www.jb.man.ac.uk/~rbeswick/3c293-paper.htm

VLBI observations of nearby radio loud Active Galactic Nuclei

We present an update of the parsec scale properties of the Bologna Complete Sample consisting of 95 radio sources from the B2 Catalog of Radio Sources and the Third Cambridge Revised Catalog (3CR), with z < 0.1. Thanks to recent new data we have now parsec scale images for 76 sources of the sample. Most of them show a one-sided jet structure but we find a higher fraction of two-sided sources in comparison with previous flux-limited VLBI surveys. A few peculiar sources are presented and discussed in more detail.Comment: 6 pages, 7 figures, Proceedings for "The Universe under the Microscope" (AHAR 2008), April 2008, to be published in Journal of Physics: Conference Series by Institute of Physics Publishing; R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros ed

Response of VIRGO detectors to pre-big-bang gravitons

The sensitivity achievable by a pair of VIRGO detectors to stochastic and isotropic gravitational wave backgrounds produced in pre-big-bang models is discussed in view of the development of a second VIRGO interferometer. We describe a semi-analytical technique allowing to compute the signal-to-noise ratio for (monotonic or non-monotonic) logarithmic energy spectra of relic gravitons of arbitrary slope. We apply our results to the case of two correlated and coaligned VIRGO detectors and we compute their achievable sensitivities. We perform our calculations both for the usual case of minimal string cosmological scenario and in the case of a non-minimal scenario where a long dilaton dominated phase is present prior to the onset of the ordinary radiation dominated phase. In this framework, we investigate possible improvements of the achievable sensitivities by selective reduction of the thermal contributions (pendulum and pendulum's internal modes) to the noise power spectra of the detectors. Since a reduction of the shot noise does not increase significantly the expected sensitivity of a VIRGO pair (in spite of the relative spatial location of the two detectors) our findings support the experimental efforts directed towards a substantial reduction of thermal noise.Comment: 23 pages in Latex styl

Spin and rotational symmetries in unrestricted Hartree Fock states of quantum dots

Ground state energies are obtained using the unrestricted Hartree Fock method for up to four interacting electrons parabolically confined in a quantum dot subject to a magnetic field. Restoring spin and rotational symmetries we recover Hund first rule. With increasing magnetic field, crossovers between ground states with different quantum numbers are found for fixed electron number that are not reproduced by the unrestricted Hartree Fock approximation. These are consistent with the ones obtained with more refined techniques. We confirm the presence of a spin blockade due to a spin mismatch in the ground states of three and four electrons.Comment: 16 Pages, 2 figures, accepted for publication on New Journal of Physic