Surprising Evolution of the Parsec-scale Faraday Rotation Gradients in the Jet of the BL Lac Object B1803+784

Several multi-frequency polarization studies have shown the presence of systematic Faraday Rotation gradients across the parsec-scale jets of Active Galactic Nuclei (AGN), taken to be due to the systematic variation of the line-of-sight component of a helical magnetic (B) field across the jet. Other studies have confirmed the presence and sense of these gradients in several sources, thus providing evidence that these gradients persist over time and over large distances from the core. However, we find surprising new evidence for a reversal in the direction of the Faraday Rotation gradient across the jet of B1803+784, for which multi-frequency polarization observations are available at four epochs. At our three epochs and the epoch of Zavala & Taylor (2003), we observe transverse Rotation Measure (RM) gradients across the jet, consistent with the presence of a helical magnetic field wrapped around the jet. However, we also observe a "flip" in the direction of the gradient between June 2000 and August 2002. Although the origins of this phenomena are not entirely clear, possibly explanations include (i) the sense of rotation of the central supermassive black hole and accretion disc has remained the same, but the dominant magnetic pole facing the Earth has changed from North to South; (ii) a change in the direction of the azimuthal B field component as a result of torsional oscillations of the jet; and (iii) a change in the relative contributions to the observed rotation measures of the "inner" and "outer" helical fields in a magnetic-tower model. Although we cannot entirely rule out the possibility that the observed changes in the RM distribution are associated instead with changes in the thermal-electron distribution in the vicinity of the jet, we argue that this explanation is unlikely.Comment: 21 pages, 10 figures. Accepted for publication in MNRA

New ex-OH maser detections in the northern celestial hemisphere

Aims.Molecular masers, including methanol and hydroxyl masers, and in particular the ones in excited rotational states (ex-OHmasers), are one of the most informative tools for studying star-forming regions. So, the discovery, of new maser sources in theseregions is of great importance. Many studies and surveys of ex-OH maser sources have been carried out in the southern celestialhemisphere, but only a few have been done in the northern hemisphere. The specific aim of this work is to close this gap.Methods.The star-forming regions in the northern hemisphere with known active methanol masers were observed to search for newex-OH maser sources with the 32 m and 16 m radio telescopes of the Ventspils International Radio Astronomy Centre (VIRAC).Results.Three OH maser lines in the excited state at the 6035 MHz in three northern hemisphere star-forming regions are detected.The maser 189.030+0.783 was previously known, but we suggest this maser is a possible variable. We confirm recent detections ofthe ex-OH masers 85.41+0.00 and 90.92+1.49 by other authors. The magnetic field strength in the masering regions is estimated byusing right circular polarization (RCP) and left circular polarization (LCP) pair splitting. The high-velocity resolution provides uswith an estimation of a comparatively small magnetic field strength for the 189.030+0.783 and 90.92+1.49 star-forming regionsComment: 6 pages 1 figure 4 table

Mechatronic approach to the design of a triaxial antenna with backlash minimization by the control system

The features and advantages of the support-rotating platforms design for the antenna systems with three axes are analyzed in the paper. The expediency of using such systems for the satellite tracking without signal losses in the zenith area relative to the coordinate of the antenna system is reasoned. It is necessary in order to expand the antenna system functionality, improve the performance of the antenna device, and increase the control system efficiency and the information reliability from the spacecraft as a whole. The developed design of the 3-axial support-rotating platform is described. The platform is built on a modular principle using of modern autonomous rotary actuators, which are combined by a special design. This approach is proposed in order to ensure backlash sampling using special software algorithms of the support-rotating device control system

Methods to improve the accuracy of guidance of terrestrial antenna station

The analysis of factors influencing accuracy of guidance of terrestrial antenna complexes and ways of improvement of a signal reception quality are considered. The above considerations are the result of authors many years practical experience in the AS ground stations setting and monitoring

Multi-frequency polarization properties of ten quasars on deca-parsec scales at z > 3

Global VLBI (EVN+VLBA) polarization observations at 5 and 8.4 GHz of ten high redshift (z > 3) quasars are presented. The core and jet brightness temperatures are found through modelling the self-calibrated uv-data with Gaussian components, which provide reliable estimates of the flux density and size of individual components. The observed high core brightness temperatures (median $T_{\rm b,\,core}=4\times10^{11}$ K) are consistent with Doppler boosted emission from a relativistic jet orientated close to the line-of-sight. This can also explain the dramatic jet bends observed for some of our sources since small intrinsic bends can be significantly amplified due to projection effects in a highly beamed relativistic jet. We also model-fit the polarized emission and, by taking the minimum angle separation between the model-fitted polarization angles at 5 and 8.4 GHz, we calculate the minimum inferred Faraday rotation measure (RM$_{\rm min}$) for each component. We also calculate the minimum intrinsic RM in the rest frame of the AGN (RM$_{\rm min}^{\rm intr}$ = RM$_{\rm min} (1+z)^2$), first subtracting the integrated (presumed foreground) RM in those cases where we felt we could do this reliably. The resulting mean core $|$RM$_{\rm min}^{\rm intr}|$ is 5580 rad m$^{-2}$, with a standard deviation of 3390 rad m$^{-2}$, for four high-z quasars for which we believe we could reliably remove the foreground RM. We find relatively steep core and jet spectral index values, with a median core spectral index of -0.3 and a median jet spectral index of -1.0. Comparing our results with RM observations of more nearby Active Galactic Nuclei at similar emitted frequencies does not provide any significant evidence for dependence of the quasar nuclear environment with redshift.Comment: Published in MNRAS. 18 pages, 7 figures, 5 table

Comparison of different methods for evaluation of wind turbine power production based on wind measurements

Investigations of the wind shear up to the height of 200 (m) on the Latvian coast of the Baltic Sea have been carried out using a Pentalum SpiDAR laser measuring complex. Based on wind speeds measurements for three levels – 30, 40 and 50 (m), assessment of the operational efficiency of the wind turbines for heights 100, 140 and 180 (m) have been performed. For comparison, this analysis involves five different approaches: the Rayleigh frequency distribution, three different Weibull frequency distributions and method based on approximation of the cubic wind speed. Results are compared with measurements on the corresponding heights