scholarly journals Gaia science alerts and the observing facilities of the Serbian-Bulgarian mini-network telescopes

2014 ◽  
pp. 85-93 ◽  
Author(s):  
G. Damljanovic ◽  
O. Vince ◽  
S. Boeva
Keyword(s):  
Active Galactic Nuclei ◽  
Reference Frame ◽  
European Space Agency ◽  
Galactic Nuclei ◽  
Long Baseline ◽  
Space Agency ◽  
Optical Domain ◽  
Celestial Reference Frame ◽  
Astronomical Station

The astrometric European Space Agency (ESA) Gaia mission was launched in December 19, 2013. One of the tasks of the Gaia mission is production of an astrometric catalog of over one billion stars and more than 500000 extragalactic sources. The quasars (QSOs), as extragalactic sources and radio emitters, are active galactic nuclei objects (AGNs) whose coordinates are well determined via Very Long Baseline Interferometry (VLBI) technique and may reach sub-milliarcsecond accuracy. The QSOs are the defining sources of the quasi-inertial International Celestial Reference Frame (ICRF) because of their core radio morphology, negligible proper motions (until sub-milliarcsecond per year), and apparent point-like nature. Compact AGNs, visible in optical domain, are useful for a direct link of the future Gaia optical reference frame with the most accurate radio one. Apart from the above mentioned activities, Gaia has other goals such as follow-up of transient objects. One of the most important Gaia's requirements for photometric alerts is a fast observation and reduction response, that is, submition of observations within 24 hours. For this reason we have developed a pipeline. In line with possibilities of our new telescope (D(cm)/F(cm)=60/600) at the Astronomical Station Vidojevica (ASV, of the Astronomical Observatory in Belgrade), we joined the Gaia-Follow-Up Network for Transients Objects (Gaia-FUN-TO) for the photometric alerts. Moreover, in view of the cooperation with Bulgarian colleagues (in the frst place, SV), one of us (GD) initiated a local mini-network of Serbian { Bulgarian telescopes useful for the Gaia-FUN-TO and other astronomical purposes. During the next year we expect a new 1.4 m telescope at ASV site. The speed of data processing (from observation to calibration server) could be one day. Here, we present an overview of our activities in the Gaia-FUN-TO which includes establishing Serbian { Bulgarian mini-network (of five telescopes at three sites, ASV in Serbia, Belogradchik and Rozhen in Bulgaria), the Gaia-FUN-TO test observations, and some results.

Linking the optically bright Gaia frame to the third International Celestial Reference Frame

2021 ◽  
Author(s):  
Susanne Lunz ◽  
James Anderson ◽  
Ming H. Xu ◽  
Robert Heinkelmann ◽  
Oleg Titov ◽  
...  
Keyword(s):  
Reference Frame ◽  
European Space Agency ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
The Third ◽  
Long Baseline ◽  
Data Release ◽  
Radio Frequencies ◽  
Celestial Reference Frame ◽  
Radio Stars

<p>The new data release of the Gaia satellite operated by the European Space Agency recently published its 3rd data release (Early Data Release 3, EDR3). The dataset contains astrometric data of about 1.8 billion objects detected at optical frequencies and therefore it outperforms any catalog of astrometric information up to date. The reference frame defined by Gaia EDR3 is aligned to the International Celestial Reference System by referring to counterparts in its realization, the third International Celestial Reference Frame (ICRF3), which is calculated from very long baseline interferometry (VLBI) observations of extragalactic objects at radio frequencies. <br>The Gaia dataset is known to be magnitude-dependent in terms of astrometric calibration. As the objects in ICRF3, although bright at radio frequencies, are mostly faint at optical frequencies, the optically bright Gaia frame has to be linked to ICRF3 by additional counterparts besides objects in ICRF3. The non-rotation of the optically bright Gaia frame is especially important as optically bright objects can, besides astrophysical studies, be used for navigation in space, where other geodetic systems like global navigation satellite systems are out of reach. Suitable additional counterparts are radio stars which are observed by VLBI relative to extragalactic objects in ICRF3. We discuss the orientation and spin differences between the optically bright Gaia EDR3 and VLBI data of radio stars and their impact on the Gaia data usage.</p>

scholarly journals Multiband RadioAstron space VLBI imaging of the jet in quasar S5 0836+710

2020 ◽  
Vol 641 ◽  
pp. A40 ◽  
Author(s):  
L. Vega-García ◽  
A. P. Lobanov ◽  
M. Perucho ◽  
G. Bruni ◽  
E. Ros ◽  
...  
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Internal Structure ◽  
Galactic Nuclei ◽  
Brightness Temperatures ◽  
Long Baseline ◽  
Space Agency ◽  
Relativistic Jet ◽  
Inverse Compton ◽  
Helical Mode

Context. Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. Aims. We present multiwavelength images made of the radio emission in the powerful quasar S5 0836+710, obtained using a global VLBI array and the antenna Spektr-R of the RadioAstron mission of the Russian Space Agency, with the goal of studying the internal structure and physics of the relativistic jet in this object. Methods. The RadioAstron observations at wavelengths of 18 cm, 6 cm, and 1.3 cm are part of the Key Science Program for imaging radio emission in strong AGN. The internal structure of the jet is studied by analyzing transverse intensity profiles and modeling the structural patterns developing in the flow. Results. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02 mas to 200 mas. Brightness temperatures in excess of 1013 K are measured in the jet, requiring Doppler factors of ≥100 for reconciling them with the inverse Compton limit. Several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin–Helmholtz (KH) instability. The oscillatory patterns are interpreted as the surface and body wavelengths of the helical mode of the KH instability. The interpretation provides estimates of the jet Mach number and of the ratio of the jet to the ambient density, which are found to be Mj ≈ 12 and η ≈ 0.33. The ratio of the jet to the ambient density should be conservatively considered an upper limit because its estimate relies on approximations.

scholarly journals The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms

Sensors ◽  
2021 ◽  
Vol 21 (24) ◽  
pp. 8276
Author(s):  
Víctor Puente ◽  
Marta Folgueira
Keyword(s):  
Stochastic Model ◽  
Least Squares ◽  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Pole ◽  
Two Factors ◽  
Least Squares Adjustment ◽  
Empirical Corrections ◽  
Celestial Reference Frame

Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.

scholarly journals Proper motion in lensed radio jets at redshift 3: A possible dual super-massive black hole system in the early Universe

2019 ◽  
Vol 630 ◽  
pp. A108 ◽  
Author(s):  
C. Spingola ◽  
J. P. McKean ◽  
D. Massari ◽  
L. V. E. Koopmans
Keyword(s):  
Active Galactic Nuclei ◽  
Early Universe ◽  
Gravitational Lensing ◽  
Proper Motion ◽  
Galactic Nuclei ◽  
Massive Black Hole ◽  
Radio Jets ◽  
Long Baseline ◽  
Multi Wavelength ◽  
Low Probability

In this paper, we exploit the gravitational lensing effect to detect proper motion in the highly magnified gravitationally lensed source MG B2016+112. We find positional shifts up to 6 mas in the lensed images by comparing two Very Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are separated by 14.359 years, and provide an astrometric accuracy of the order of tens of μas. From lens modelling, we exclude a shift in the lensing galaxy as the cause of the positional change of the lensed images, and we assign it to the background source. The source consists of four sub-components separated by ∼175 pc, with proper motion of the order of tens μas yr−1 for the two components at highest magnification (μ ∼ 350) and of the order of a few mas yr−1 for the two components at lower magnification (μ ∼ 2). We propose single active galactic nuclei (AGN) and dual AGN scenarios to explain the source plane. Although, the latter interpretation is supported by the archival multi-wavelength properties of the object. In this case, MG B2016+112 would represent the highest redshift dual radio-loud AGN system discovered thus far, and would support the merger interpretation for such systems. Also, given the low probability (∼10−5) of detecting a dual AGN system that is also gravitationally lensed, if confirmed, this would suggest that such dual AGN systems must be more abundant in the early Universe than currently thought.

scholarly journals Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

2018 ◽  
Vol 614 ◽  
pp. A74 ◽  
Author(s):  
F. J. Abellán ◽  
I. Martí-Vidal ◽  
J. M. Marcaide ◽  
J. C. Guirado
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Polar Cap ◽  
Motion Constraints ◽  
The Core ◽  
Long Baseline ◽  
Precision Phase ◽  
First Time ◽  
Core Shift

We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σ level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.

scholarly journals Inferring the jet parameters of active galactic nuclei using Bayesian analysis of VLBI data with a non-uniform jet model

2019 ◽  
Vol 488 (1) ◽  
pp. 939-953 ◽  
Author(s):  
Ilya N Pashchenko ◽  
Alexander V Plavin
Keyword(s):  
Bayesian Analysis ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Peak Frequency ◽  
Physical Parameters ◽  
Image Deconvolution ◽  
Long Baseline ◽  
Central Engine ◽  
Electron Positron ◽  
Vlbi Data

ABSTRACTThe physical parameters of the jets of active galactic nuclei observed with Very Long Baseline Interferometry (VLBI) are usually inferred from core-shift measurements or from the flux and size measured at the peak frequency of the synchrotron spectrum. Both methods are preceded by modelling the observed VLBI jet structure with simple Gaussian templates. Here we infer the jet parameters using an inhomogeneous jet model directly, bypassing the modelling of the source structure with a Gaussian template or image deconvolution. We apply Bayesian analysis to multifrequency VLBA observations of radio galaxy NGC 315 and find that its parsec-scale jet is well described by an inhomogeneous conical model. Our results favour an electron–positron jet. We also detect a component as a part of a counter jet. Its position implies the presence of an external absorber with a steep density gradient close (r = 0.1 pc) to the central engine.

scholarly journals Localization of binary black hole mergers with known inclination

2019 ◽  
Vol 488 (3) ◽  
pp. 4459-4463 ◽  
Author(s):  
K Rainer Corley ◽  
Imre Bartos ◽  
Leo P Singer ◽  
Andrew R Williamson ◽  
Zoltán Haiman ◽  
...  
Keyword(s):  
Black Hole ◽  
Binary System ◽  
Active Galactic Nuclei ◽  
Prior Information ◽  
Galactic Nuclei ◽  
Electromagnetic Emission ◽  
Accretion Discs ◽  
Host Galaxies ◽  
Binary Black Hole

ABSTRACT The localization of stellar-mass binary black hole mergers using gravitational waves is critical in understanding the properties of the binaries’ host galaxies, observing possible electromagnetic emission from the mergers, or using them as a cosmological distance ladder. The precision of this localization can be substantially increased with prior astrophysical information about the binary system. In particular, constraining the inclination of the binary can reduce the distance uncertainty of the source. Here, we present the first realistic set of localizations for binary black hole mergers, including different prior constraints on the binaries’ inclinations. We find that prior information on the inclination can reduce the localization volume by a factor of 3. We discuss two astrophysical scenarios of interest: (i) follow-up searches for beamed electromagnetic/neutrino counterparts and (ii) mergers in the accretion discs of active galactic nuclei.

scholarly journals The Milliarcsecond Structure of Active Galactic Nuclei Observed with VLBI

1989 ◽  
Vol 134 ◽  
pp. 525-528
Author(s):  
T. J. Pearson ◽  
A. C. S. Readhead
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Relativistic Motion ◽  
Powerful Radio ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Central Engine

Very Long Baseline Interferometry at radio wavelengths is the only technique available for imaging the central few parsecs of powerful radio galaxies and quasars. VLBI observations have shown that in many nuclei radio-emitting material is collimated into a jet on a scale less than a parsec and ejected at relativistic velocities. The interpretation of the observations is complicated by the relativistic motion, however: the images are dominated by those parts of the source that are moving almost directly towards the observer, and thus amplified by relativistic aberration. Nonetheless, the VLBI images are vital for understanding the nature of the central engine, the cause of the collimation, and the physics of the jets.

Very long baseline interferometry polarization studies of quasars and active galactic nuclei

1986 ◽  
Vol 64 (4) ◽  
pp. 434-439 ◽  
Author(s):  
J. F. C. Wardle ◽  
D. H. Roberts
Keyword(s):  
Active Galactic Nuclei ◽  
Linear Polarization ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
First Results ◽  
Polarization Studies ◽  
Theoretical Issues

We present some first results of a program to map the distribution of linear polarization in compact radio sources with milliarcsecond resolution. We show first-epoch maps of 3C345 and 0735 + 178 and first- and second-epoch maps of OJ287. In general, the polarization is mainly associated with optically thin (jet) components. In the case of OJ287, polarization maps made 1 year apart are strikingly different. We also discuss some of the theoretical issues raised by these observations.

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