426 research outputs found
The amplifier of unipolar pulses of the short range radar system
The amplifier of videopulses intended for work as a source of a pulse feed of the Hannah diodes 3Π763Π-M of the short range radar system is described. Characteristics of the amplifier are: coefficient of amplification 16 dB; the maximal amplitude of output pulses - 6 V; the maximal current in a pulse - 2,5 A
Structure of the Radio Source 3C 120 at 8.4 GHz from VLBA+ Observations in 2002
Maps of the radio source 3C 120 obtained from VLBA+ observations at 8.4 GHz
at five epochs in January - September 2002 are presented. The images were
reconstructed using the maximum entropy method and the Pulkovo VLBImager
software package for VLBI mapping. Apparent superluminal motions of the
brightest jet knots have been estimated. The speeds of jet knots decreases with
distance from the core, changing from 5.40+-0.48c $ to 2.00+-0.48c over 10 mas
(where c is the speed of light) for a Hubble constant of 65 km/s/Mpc. This can
be explained by interaction of the jet with the medium through which it
propagates.Comment: 9 pages, 6 figures, 5 table
Opacity in compact extragalactic radio sources and its effect on radio-optical reference frame alignment
Accurate alignment of the radio and optical celestial reference frames
requires detailed understanding of physical factors that may cause offsets
between the positions of the same object measured in different spectral bands.
Opacity in compact extragalactic jets (due to synchrotron self-absorption and
external free-free absorption) is one of the key physical phenomena producing
such an offset, and this effect is well-known in radio astronomy ("core
shift"). We have measured the core shifts in a sample of 29 bright compact
extragalactic radio sources observed using very long baseline interferometry
(VLBI) at 2.3 and 8.6 GHz. We report the results of these measurements and
estimate that the average shift between radio and optical positions of distant
quasars would be of the order of 0.1-0.2 mas. This shift exceeds positional
accuracy of GAIA and SIM. We suggest two possible approaches to carefully
investigate and correct for this effect in order to align accurately the radio
and optical positions. Both approaches involve determining a Primary Reference
Sample of objects to be used for tying the radio and optical reference frames
together.Comment: 4 pages, 1 figure; to appear in IAU Symposium 248 Proceedings, "A
Giant Step: from Milli- to Micro-arcsecond Astrometry", eds. W.-J. Jin, I.
Platais, M. Perryma
Finite-sample and asymptotic sign-based tests for parameters of non-linear quantile regression with Markov noise
One of the most noticeable features of sign-based statistical procedures is an opportunity to build an exact test for simple hypothesis testing of parameters in a regression model. In this article, we expanded a sing-based approach to the nonlinear case with dependent noise. The examined model is a multi-quantile regression, which makes it possible to test hypothesis not only of regression parameters, but of noise parameters as well
The connection between the radio jet and the gamma-ray emission in the radio galaxy 3C 120
We present the analysis of the radio jet evolution of the radio galaxy 3C 120
during a period of prolonged gamma-ray activity detected by the Fermi satellite
between December 2012 and October 2014. We find a clear connection between the
gamma-ray and radio emission, such that every period of gamma-ray activity is
accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new
superluminal component. However, not all ejections of components are associated
with gamma-ray events detectable by Fermi. Clear gamma-ray detections are
obtained only when components are moving in a direction closer to our line of
sight.This suggests that the observed gamma-ray emission depends not only on
the interaction of moving components with the mm-VLBI core, but also on their
orientation with respect to the observer. Timing of the gamma-ray detections
and ejection of superluminal components locate the gamma-ray production to
within almost 0.13 pc from the mm-VLBI core, which was previously estimated to
lie about 0.24 pc from the central black hole. This corresponds to about twice
the estimated extension of the broad line region, limiting the external photon
field and therefore suggesting synchrotron self Compton as the most probable
mechanism for the production of the gamma-ray emission. Alternatively, the
interaction of components with the jet sheath can provide the necessary photon
field to produced the observed gamma-rays by Compton scattering.Comment: Already accepted for publication in The Astrophysical Journa
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