The Influence of Propagation through the Irregular Interstellar Plasma on VLBI Observations

1988 ◽  
pp. 287-294 ◽  
Author(s):  
B. J. Rickett ◽  
W. A. Coles
Keyword(s):  
Vlbi Observations ◽  
Interstellar Plasma

scholarly journals The Influence of Propagation through the Irregular Interstellar Plasma on VLBI Observations

1988 ◽  
Vol 129 ◽  
pp. 287-294
Author(s):  
B.J. Rickett ◽  
W.A. Coles
Keyword(s):  
Interstellar Medium ◽  
Radio Sources ◽  
Vlbi Observations ◽  
Interstellar Plasma ◽  
Interstellar Scattering ◽  
Galactic Sources

It has been known since pulsars were discovered that the interstellar medium (ISM) can cause angular broadening of radio sources. However, the amount of scattering along typical lines of sight to extra-galactic sources is not large enough to cause any loss of visibility, even on intercontinental baselines, unless the frequency is below about 100 MHz. Recent studies have shown that interstellar scattering (ISS) can have considerably stronger effects; this paper addresses their relevance to VLBI.

A large rotating structure around AB Doradus A at VLBI scale

2019 ◽  
Vol 15 (S354) ◽  
pp. 189-194
Author(s):  
J. B. Climent ◽  
J. C. Guirado ◽  
R. Azulay ◽  
J. M. Marcaide
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Complex Structure ◽  
Main Sequence Star ◽  
Polar Cap ◽  
Vlbi Observations ◽  
Rotating Structure ◽  
Source Structure ◽  
Expected Position

AbstractWe report the results of three VLBI observations of the pre-main-sequence star AB Doradus A at 8.4 GHz. With almost three years between consecutive observations, we found a complex structure at the expected position of this star for all epochs. Maps at epochs 2007 and 2010 show a double core-halo morphology while the 2013 map reveals three emission peaks with separations between 5 and 18 stellar radii. Furthermore, all maps show a clear variation of the source structure within the observing time. We consider a number of hypothesis in order to explain such observations, mainly: magnetic reconnection in loops on the polar cap, a more general loop scenario and a close companion to AB Dor A.

Improved UT1 Predictions through Low-Latency VLBI Observations

2010 ◽  
Author(s):  
Brian Luzum ◽  
Axel Nothnagel
Keyword(s):  
Low Latency ◽  
Vlbi Observations

Finding AGN with wide-eld VLBI observations

2011 ◽  
Author(s):  
Enno Middelberg ◽  
Adam Deller ◽  
John Morgan ◽  
Helge Rottmann ◽  
Walter Alef ◽  
...  
Keyword(s):  
Vlbi Observations

Masers as probes of the gas dynamics close to forming high-mass stars

2017 ◽  
Vol 13 (S336) ◽  
pp. 201-206 ◽  
Author(s):  
Luca Moscadelli ◽  
Alberto Sanna ◽  
Ciriaco Goddi
Keyword(s):  
Gas Dynamics ◽  
Very Long Baseline Interferometry ◽  
High Mass ◽  
Powerful Technique ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Massive Forming ◽  
Typical Distances ◽  
New Generation ◽  
Better Than

AbstractImaging the inner few 1000 AU around massive forming stars, at typical distances of several kpc, requires angular resolutions of better than 0″.1. Very Long Baseline Interferometry (VLBI) observations of interstellar molecular masers probe scales as small as a few AU, whereas (new-generation) centimeter and millimeter interferometers allow us to map scales of the order of a few 100 AU. Combining these informations all together, it presently provides the most powerful technique to trace the complex gas motions in the proto-stellar environment. In this work, we review a few compelling examples of this technique and summarize our findings.

scholarly journals 3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

2021 ◽  
Vol 502 (2) ◽  
pp. 1843-1855
Author(s):  
Antonios Nathanail ◽  
Ramandeep Gill ◽  
Oliver Porth ◽  
Christian M Fromm ◽  
Luciano Rezzolla
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Opening Angle ◽  
Hollow Core ◽  
Binary Neutron Star ◽  
Vlbi Observations ◽  
Superluminal Motion ◽  
General Relativistic ◽  
Star Binary ◽  
Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

scholarly journals VLBI Observations of the Radio Jet in 3C 273

1988 ◽  
Vol 129 ◽  
pp. 27-28
Author(s):  
S. C. Unwin ◽  
R. J. Davis
Keyword(s):  
Dynamic Range ◽  
Large Range ◽  
High Dynamic Range ◽  
No Emission ◽  
The Core ◽  
Vlbi Observations ◽  
High Dynamic ◽  
Quasar 3C 273

We present a new high dynamic range map of the quasar 3C 273, made from observations with a VLBI network of 12 telescopes. This new map at 18 cm wavelength has one of the highest dynamic ranges yet achieved with VLBI, and it shows the ‘jet’ extending to at least 180 milliarcsec, or 330 pc from the nucleus of the quasar. Strong limits can be placed on the brightness of any ‘counter-jet’ on kiloparsec-scales, as no emission is visible on the opposite side of the ‘core’. Combining with other VLBI, VLA and MERLIN maps shows that the jet is visible and continuous over a very large range of scales, from 1 pc to 40 kpc.

scholarly journals VLBI Pulsar Astrometry

2001 ◽  
Vol 205 ◽  
pp. 404-407
Author(s):  
R.M. Campbell
Keyword(s):  
Proper Motion ◽  
Vlbi Observations ◽  
Recent Developments

I briefly review the means by which VLBI observations can determine the position, proper motion, and parallax of a pulsar, consider a subset of the applications of such results, and highlight recent developments in pulsar gating at JIVE.

scholarly journals Serendipitous VLBI Observations of Intraday Variability in the BL Lac Objects 1334–127, 2131–021, and 2155–152

1998 ◽  
Vol 164 ◽  
pp. 273-274
Author(s):  
P. Yu. Kochanev ◽  
D. C. Gabuzda
Keyword(s):  
Rapid Variability ◽  
Bl Lac Objects ◽  
Polarization Structure ◽  
Vlbi Observations ◽  
Bl Lac ◽  
Vlbi Data ◽  
Intraday Variability

AbstractGlobal λ = 6 cm VLBI polarization observations of intraday variability in the three BLLacertae objects 1334–127, 2131–021, and 2155–152 are analyzed. Integrated VLA measurements during the VLBI observations show that although there were no substantial total intensity variations, the polarizations for these three sources varied significantly during the VLBI experiment. The VLBI data were divided into 2-3 hour segments in order to search for corresponding rapid variability in the VLBI polarization structure. Our analysis shows that the VLA polarization variability in 2155–152 and 2131–021 is present in the VLBI data (i.e., it occurred on mas scales), but this is not the case for 1334–127.

scholarly journals On the nature of protostellar H2O masers

1987 ◽  
Vol 122 ◽  
pp. 141-142
Author(s):  
G. M. Rudnitskij
Keyword(s):  
Active Phase ◽  
Young Star ◽  
Line Profiles ◽  
Free Electrons ◽  
Heavy Particles ◽  
Vlbi Observations ◽  
Generation Region ◽  
Star Formation Regions ◽  
Maser Radio ◽  
Two Temperature

Most sources of B2O maser radio emission at 1.35 cm, associated with star formation regions, show strong variability with, sometimes, rapid bursts of emission (see, e.g., Liljeström 1984, Rowland and Cohen 1986, and references therein). A preliminary conclusion on the possible cyclicity of H2O maser variability can be drawn (Lekht et al. 1982, 1983), with a quasiperiod of several years. The “quiet” state of a maser source, with moderate, slowly varying values of the line flux density, turns to the “active” phase with H2O line bursts (Lekht et al. 1983). The H2O maser generation region is probably located in a rotating gas-and-dust disc (torus) around a protostar (or young star). This is pointed to by VLBI observations showing in some sources maser features arranged in an ellipsoidal structure around a common centre (presumably, the protostellar object - see Downes et al. 1979), as well as by symmetrical character of E2O line profiles of many masers (Lekht et al. 1982). As an excitation mechanism for H2O, collisional pumping in two-temperature medium behind a shock front (with hot heavy particles and cold free electrons or vice versa) is widely accepted (Bolgova et al. 1982, Kylafis and Norman 1986).

Sign in / Sign up

Export Citation Format

Share Document