scholarly journals Effelsberg Monitoring of a Sample of RadioAstron Blazars

2017 ◽  
Author(s):  
Jun Liu ◽  
Thomas P. Krichbaum ◽  
Xiang Liu ◽  
Alex Kraus ◽  
Hayley Bignall ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Flux Density ◽  
Radio Telescope ◽  
Galactic Nuclei ◽  
High Brightness ◽  
Space Radio Telescope ◽  
Long Baseline ◽  
Interstellar Scintillation ◽  
Flux Monitoring ◽  
Long Baselines

The launch of the RadioAstron space radio telescope provides a unique opportunity to study the extreme high brightness temperature of Active Galactic Nuclei (AGNs) with unprecedented long baselines of up to 28 Earth diameters. A coordinated ground-based flux density monitoring of RadioAstron targets is essential to determine the effect of interstellar scintillation (ISS) on the Space Very Long Baseline Interferometry (SVLBI) visibilities. Moreover, a combination/comparison of scintillation with SVLBI observations is expected to reveal the relative influence of source brightness temperature, compactness, and properties of the interstellar medium on the observed variability at centimeter wavelengths. In 2014 we started a RadioAstron target triggered flux monitoring with the Effelsberg 100-m radio telescope in support of this SVLBI mission. A total of 112 targets were observed during the five-session monitoring performed so far. In this paper we present a statistical study on the short-term flux density variability of the sample, which is focused on the variability characteristics and derived physical properties of the observed sources.

scholarly journals Probing the ionosphere by the pulsar B0950+08 with help of RadioAstron ground-space baselines

2019 ◽  
Vol 491 (4) ◽  
pp. 5843-5851
Author(s):  
Vladimir I Zhuravlev ◽  
Yu I Yermolaev ◽  
A S Andrianov
Keyword(s):  
Geomagnetic Storm ◽  
Radio Telescope ◽  
Preliminary Analysis ◽  
Very Long Baseline Interferometry ◽  
Electron Content ◽  
Ionospheric Disturbances ◽  
Total Electron ◽  
Space Radio Telescope ◽  
Long Baseline ◽  
Ionospheric Total Electron Content

ABSTRACT The ionospheric scattering of pulses emitted by PSR B0950+08 is measured using the 10-mRadioAstron Space Radio Telescope, the 300-m Arecibo Radio Telescope, and the 14 x 25-m Westerbork Synthesis Radio Telescope (WSRT) at a frequency band between 316 and 332 MHz. We analyse this phenomenon based on a simulated model of the phase difference obtained between antennas that are widely separated by nearly 25 Earth diameters. We present a technique for processing and analysing the ionospheric total electron content (TEC) at the ground stations of the ground-space interferometer. This technique allows us to derive almost synchronous half-hour structures of the TEC in the ionosphere at an intercontinental distance between the Arecibo and WSRT stations. We find that the amplitude values of the detected structures are approximately twice as large as the values for the TEC derived in the international reference ionosphere (IRI) project. Furthermore, the values of the TEC outside these structures are almost the same as the corresponding values found by the IRI. According to a preliminary analysis, the detected structures were observed during a geomagnetic storm with a minimum Dst index of ∼75 nT generated by interplanetary disturbances, and may be due to the influence of interplanetary and magnetospheric phenomena on ionospheric disturbances. We show that the Space Very Long Baseline Interferometry provides us with new opportunities to study the TEC, and we demonstrate the capabilities of this instrument to research the ionosphere.

scholarly journals Space-VLBI observations of OH masers

2002 ◽  
Vol 206 ◽  
pp. 105-111 ◽  
Author(s):  
Vyacheslav I. Slysh ◽  
Maxim A. Voronkov ◽  
Irina E. Val'tts ◽  
Victor Migenes ◽  
K.M. Shibata ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Lower Limit ◽  
Radio Telescope ◽  
Angular Resolution ◽  
Main Line ◽  
Radio Telescopes ◽  
Space Radio Telescope ◽  
Vlbi Observations ◽  
Interstellar Scattering

We report on the first space-VLBI observations of the OH masers in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The maps of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6 × 1012 K was obtained. The masers seem to be located in the direction of low interstellar scattering.

THE UNUSUAL EMISSION STRUCTURE 140 PC FROM THE CORE IN THE JET OF THE RADIO GALAXY 3C 120

2012 ◽  
Vol 08 ◽  
pp. 315-318
Author(s):  
CAROLINA CASADIO ◽  
JOSÉ L. GÓMEZ ◽  
MAR ROCA-SOGORB ◽  
IVÁN AGUDO
Keyword(s):  
Brightness Temperature ◽  
Flux Density ◽  
Radio Galaxy ◽  
The Core ◽  
Long Baseline ◽  
Very Long Baseline Array ◽  
3C 120

We present Very Long Baseline Array observations of the radio galaxy 3C 120 during 2010, revealing the existence of a very unusual component (hereafter C80) located at 80 mas (deprojected to 140 pc) with a brightness temperature ≈ 600 times higher than expected at such distance from the core. No significant changes in the position and flux density of C80 has been observed from its discovered up to these new observations suggesting that it may be associated with a strong recollimation shock. Components downstream of C80 move at superluminal velocities, resembling the situation near the HST-1 component in M87.

scholarly journals Intraday Variability in Northern Hemisphere Radio Sources

2002 ◽  
Vol 19 (1) ◽  
pp. 14-18 ◽  
Author(s):  
T. P. Krichbaum ◽  
A. Kraus ◽  
L. Fuhrmann ◽  
G. Cimò ◽  
A. Witzel
Keyword(s):  
Flux Density ◽  
Radio Telescope ◽  
Physical Interpretation ◽  
Radio Sources ◽  
Intrinsic Variability ◽  
The Past ◽  
Interstellar Scintillation ◽  
Variability Pattern ◽  
Complex Source ◽  
Intraday Variability

AbstractWe summarise results from flux density monitoring campaigns performed with the 100 m radio telescope at Effelsberg and the VLA during the past 15 yrs. We briefly discuss some of the statistical properties from now more than 40 high declination sources (δ ≥ 30°), which show intraday variability (IDV). In general, IDV is more pronounced for sources with flat radio spectra and compact VLBI structures. For 0917+62, we present new VLBI images which suggest that the variability pattern is modified by the occurrence of new jet components. For 0716+71, we show the first detection of IDV at millimetre wavelengths (32 GHz). For the physical interpretation of the IDV phenomenon, a complex source and frequency dependent superposition of interstellar scintillation and source intrinsic variability should be considered.

scholarly journals Intraday Variability and Microarcsecond Structure in Blazar Cores

2001 ◽  
Vol 205 ◽  
pp. 84-87 ◽  
Author(s):  
David L. Jauncey ◽  
Lucyna Kedziora-Chudczer ◽  
J. E. J. Lovell ◽  
Jean-Pierre Macquart ◽  
George D. Nicolson ◽  
...  
Keyword(s):  
William Shakespeare ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Julius Caesar ◽  
Principal Mechanism ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Intraday Variability

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory. “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar

scholarly journals Flux Monitoring Using the Toruń 32-m Radio Telescope

2004 ◽  
Vol 218 ◽  
pp. 441-442
Author(s):  
J. Kijak ◽  
Y. Gupta ◽  
W. Lewandowski ◽  
G. Hrynek ◽  
K. Krzeszowski
Keyword(s):  
Flux Density ◽  
Radio Telescope ◽  
Density Measurements ◽  
Flux Monitoring ◽  
One Year

We present flux density measurements for PSR B0329+54 at 4.8 GHz obtained during one year.

scholarly journals Searching for obscured AGN in z ∼ 2 submillimetre galaxies

2020 ◽  
Vol 638 ◽  
pp. A113 ◽  
Author(s):  
H. Chen ◽  
M. A. Garrett ◽  
S. Chi ◽  
A. P. Thomson ◽  
P. D. Barthel ◽  
...  
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Source Population ◽  
Host Galaxies ◽  
Star Forming ◽  
Long Baseline ◽  
Good Guide

Aims. Submillimetre-selected galaxies (SMGs) at high redshift (z ∼ 2) are potential host galaxies of active galactic nuclei (AGN). If the local Universe is a good guide, ∼50% of the obscured AGN amongst the SMG population could be missed even in the deepest X-ray surveys. Radio observations are insensitive to obscuration; therefore, very long baseline interferometry (VLBI) can be used as a tool to identify AGN in obscured systems. A well-established upper limit to the brightness temperature of 105 K exists in star-forming systems, thus VLBI observations can distinguish AGN from star-forming systems via brightness temperature measurements. Methods. We present 1.6 GHz European VLBI Network (EVN) observations of four SMGs (with measured redshifts) to search for evidence of compact radio components associated with AGN cores. For two of the sources, e-MERLIN images are also presented. Results. Out of the four SMGs observed, we detect one source, J123555.14, that has an integrated EVN flux density of 201 ± 15.2 μJy, corresponding to a brightness temperature of 5.2 ± 0.7 × 105 K. We therefore identify that the radio emission from J123555.14 is associated with an AGN. We do not detect compact radio emission from a possible AGN in the remaining sources (J123600.10, J131225.73, and J163650.43). In the case of J131225.73, this is particularly surprising, and the data suggest that this may be an extended, jet-dominated AGN that is resolved by VLBI. Since the morphology of the faint radio source population is still largely unknown at these scales, it is possible that with a ∼10 mas resolution, VLBI misses (or resolves) many radio AGN extended on kiloparsec scales.

scholarly journals Apparent superluminal core expansion and limb brightening in the candidate neutrino blazar TXS 0506+056

2019 ◽  
Vol 633 ◽  
pp. L1 ◽  
Author(s):  
E. Ros ◽  
M. Kadler ◽  
M. Perucho ◽  
B. Boccardi ◽  
H.-M. Cao ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Flux Density ◽  
Gamma Ray ◽  
High Energy ◽  
Density Increase ◽  
High Energy Neutrino ◽  
The Core ◽  
Neutrino Event ◽  
Long Baseline ◽  
Radio Outburst

Context. IceCube has reported a very-high-energy neutrino (IceCube-170922A) in a region containing the blazar TXS 0506+056. Correlated gamma-ray activity has led to the first high-probability association of a high-energy neutrino with an extragalactic source. This blazar has been found to be in a radio outburst during the neutrino event. Aims. Our goal is to probe the sub-milliarcsecond properties of the radio jet right after the neutrino detection and during the further evolution of the radio outburst. Methods. We performed target of opportunity observations at 43 GHz frequency using very long baseline interferometry imaging, corresponding to 7 mm in wavelength, with the Very Long Baseline Array two and eight months after the neutrino event. Results. We produced two images of the radio jet of TXS 0506+056 at 43 GHz with angular resolutions of (0.2 × 1.1) mas and (0.2 × 0.5) mas, respectively. The source shows a compact, high brightness temperature core, albeit not approaching the equipartition limit and a bright and originally very collimated inner jet. Beyond approximately 0.5 mas from the millimeter-VLBI core, the jet loses this tight collimation and expands rapidly. During the months after the neutrino event associated with this source, the overall flux density is rising. This flux density increase happens solely within the core. Notably, the core expands in size with apparent superluminal velocity during these six months so that the brightness temperature drops by a factor of three despite the strong flux density increase. Conclusions. The radio jet of TXS 0506+056 shows strong signs of deceleration and/or a spine-sheath structure within the inner 1 mas, corresponding to about 70–140 pc in deprojected distance, from the millimeter-VLBI core. This structure is consistent with theoretical models that attribute the neutrino and gamma-ray production in TXS 0506+056 to interactions of electrons and protons in the highly relativistic jet spine with external photons originating from a slower moving jet region. Proton loading due to jet-star interactions in the inner host galaxy is suggested as the possible cause of deceleration.

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