Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.Comment: 9 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

Extragalactic Relativistic Jets and Nuclear Regions in Galaxies

Past years have brought an increasingly wider recognition of the ubiquity of relativistic outflows (jets) in galactic nuclei, which has turned jets into an effective tool for investigating the physics of nuclear regions in galaxies. A brief summary is given here of recent results from studies of jets and nuclear regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B. Leibundgut (Springer: Heidelberg 2006

Neutrino spin rotation in dense matter and electromagnetic field

Exact solutions of the Dirac--Pauli equation for massive neutrino with anomalous magnetic moment interacting with dense matter and strong electromagnetic field are found. The complete system of neutrino wavefunctions, which show spin rotation properties are obtained and their possible applications are discussed.Comment: 11 pages, latex, misprints are correcte

Spin light of neutrino in gravitational fields

We predict a new mechanism for the spin light of neutrino ($SL\nu$) that can be emitted by a neutrino moving in gravitational fields. This effect is studied on the basis of the quasiclassical equation for the neutrino spin evolution in a gravitational field. It is shown that the gravitational field of a rotating object, in the weak-field limit, can be considered as an axial vector external field which induces the neutrino spin procession. The corresponding probability of the neutrino spin oscillations in the gravitational field has been derived for the first time. The considered in this paper $SL\nu$ can be produced in the neutrino spin-flip transitions in gravitational fields. It is shown that the total power of this radiation is proportional to the neutrino gamma factor to the fourth power, and the emitted photon energy, for the case of an ultra relativistic neutrino, could span up to gamma-rays. We investigate the $SL\nu$ caused by both gravitational and electromagnetic fields, also accounting for effects of arbitrary moving and polarized matter, in various astrophysical environments. In particular, we discuss the $SL\nu$ emitted by a neutrino moving in the vicinity of a rotating neutron star, black hole surrounded by dense matter, as well as by a neutrino propagating in the relativistic jet from a quasar.Comment: 14 pages in LaTex with 1 eps figure; derivation of the neutrino spin oscillations probability in gravitational fields and several clarifying notes are added, typos correcte

Essential spectra of difference operators on \sZ^n-periodic graphs

Let (\cX, \rho) be a discrete metric space. We suppose that the group \sZ^n acts freely on $X$ and that the number of orbits of $X$ with respect to this action is finite. Then we call $X$ a \sZ^n-periodic discrete metric space. We examine the Fredholm property and essential spectra of band-dominated operators on $l^p(X)$ where $X$ is a \sZ^n-periodic discrete metric space. Our approach is based on the theory of band-dominated operators on \sZ^n and their limit operators. In case $X$ is the set of vertices of a combinatorial graph, the graph structure defines a Schr\"{o}dinger operator on $l^p(X)$ in a natural way. We illustrate our approach by determining the essential spectra of Schr\"{o}dinger operators with slowly oscillating potential both on zig-zag and on hexagonal graphs, the latter being related to nano-structures

Large orders in strong-field QED

We address the issue of large-order expansions in strong-field QED. Our approach is based on the one-loop effective action encoded in the associated photon polarisation tensor. We concentrate on the simple case of crossed fields aiming at possible applications of high-power lasers to measure vacuum birefringence. A simple next-to-leading order derivative expansion reveals that the indices of refraction increase with frequency. This signals normal dispersion in the small-frequency regime where the derivative expansion makes sense. To gain information beyond that regime we determine the factorial growth of the derivative expansion coefficients evaluating the first 80 orders by means of computer algebra. From this we can infer a nonperturbative imaginary part for the indices of refraction indicating absorption (pair production) as soon as energy and intensity become (super)critical. These results compare favourably with an analytic evaluation of the polarisation tensor asymptotics. Kramers-Kronig relations finally allow for a nonperturbative definition of the real parts as well and show that absorption goes hand in hand with anomalous dispersion for sufficiently large frequencies and fields.Comment: 26 pages, 6 figure

The core shift effect in the blazar 3C 454.3

Opacity-driven shifts of the apparent VLBI core position with frequency (the "core shift" effect) probe physical conditions in the innermost parts of jets in active galactic nuclei. We present the first detailed investigation of this effect in the brightest gamma-ray blazar 3C454.3 using direct measurements from simultaneous 4.6-43 GHz VLBA observations, and a time lag analysis of 4.8-37 GHz lightcurves from the UMRAO, CrAO, and Metsahovi observations in 2007-2009. The results support the standard Konigl model of jet physics in the VLBI core region. The distance of the core from the jet origin r_c(nu), the core size W(nu), and the lightcurve time lag DT(nu) all depend on the observing frequency nu as r_c(nu)~W(nu)~ DT(nu)~nu^-1/k. The obtained range of k=0.6-0.8 is consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. The similar frequency dependence of r_c(nu) and W(nu) suggests that the external pressure gradient does not dictate the jet geometry in the cm-band core region. Assuming equipartition, the magnetic field strength scales with distance r as B = 0.4(r/1pc)^-0.8 G. The total kinetic power of electron/positron jet is about 10^44 ergs/s.Comment: Accepted for publication in MNRAS; 10 pages, 6 figure