scholarly journals VLBI Observations of Southern Gamma-Ray Sources. III

2018 ◽  
Vol 35 ◽  
Author(s):  
P. G. Edwards ◽  
R. Ojha ◽  
R. Dodson ◽  
J. E. J. Lovell ◽  
J. E. Reynolds ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Spectral Index ◽  
Gamma Ray ◽  
Published Data ◽  
High Brightness ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Made In

AbstractWe report the results of Long Baseline Array observations made in 2001 of ten southern sources proposed by Mattox et al. as counterparts to EGRET >100 MeV gamma-ray sources. Source structures are compared with published data where available and possible superluminal motions identified in several cases. The associations are examined in the light of Fermi observations, indicating that the confirmed counterparts tend to have radio properties consistent with other identifications, including flat radio spectral index, high brightness temperature, greater radio variability, and higher core dominance.

scholarly journals Space VLBI Observations of PKS 1921-293

2001 ◽  
Vol 205 ◽  
pp. 128-129
Author(s):  
Zhi-Qiang Shen ◽  
Philip G. Edwards ◽  
Seiji Kameno ◽  
Makoto Inoue ◽  
James E. J. Lovell
Keyword(s):  
Brightness Temperature ◽  
Spectral Index ◽  
Rest Frame ◽  
The Core ◽  
Vlbi Observations ◽  
First Time

We present results of the first space VLBI observations of PKS 1921-293. An inner jet component about 1.5 mas north of the core is revealed for the first time. The compact core is partially resolved, but still has a brightness temperature (at the source rest frame) of 3.0×1012 K. A spectral index map made by combining the 1.6 GHz VSOP image with the 5.0 GHz VLBA+Y image at the first epoch is also presented.

scholarly journals Recent developments in supernova research with VLBI

2013 ◽  
Vol 9 (S296) ◽  
pp. 53-57 ◽  
Author(s):  
Norbert Bartel ◽  
Michael F. Bietenholz
Keyword(s):  
Very Long Baseline Interferometry ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Expansion Velocity ◽  
Radial Density ◽  
Density Profiles ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Recent Developments ◽  
Circumstellar Medium

AbstractVery long baseline interferometry (VLBI) observations during the last 30 years have resolved many supernovae and provided detailed measurements of the expansion velocity and deceleration. Such measurements are useful for estimating the radial density profiles of both the ejecta and the circumstellar medium left over from the progenitor. VLBI measurements are also the most direct way of confirming the relativistic expansion velocities thought to occur in supernovae associated with gamma-ray bursts. Well-resolved images of a few supernovae have been obtained, and the interaction of the ejecta as it expands into the circumstellar medium could be monitored in detail. We discuss recent results, for SN 1979C, SN 1986J, and SN 1993J, and note that updated movies of the latter two of the supernovae from soon after the explosion to the present are available from the first author's personal website.

scholarly journals VLBI Observations of the V=1 and V=2 SiO Masers in W Hydra and VX Sagittarius

1980 ◽  
Vol 87 ◽  
pp. 535-536 ◽  
Author(s):  
A. P. Lane ◽  
P. T. P. Ho ◽  
C. R. Predmore ◽  
J. M. Moran ◽  
R. Genzel ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Angular Size ◽  
Energy Separation ◽  
Equivalent Temperature ◽  
Late Type ◽  
Circumstellar Envelopes ◽  
Vibrational States ◽  
High Brightness ◽  
Mira Variable ◽  
Vlbi Observations

Our previous observations established the small angular size and high brightness temperature of emission from the v=1, J=1-0 transition of SiO from the circumstellar envelopes of the supergiant VX Sgr and the Mira variable R Cas. We performed a second VLBI experiment on the SiO masers in several late type stars on 31 Oct.-2 Nov. 1978 to compare the physical characteristics of the SiO masers in the v=1 and v=2 states. With an energy separation of 1258 cm-1 (an equivalent temperature of 1753 K) between the two vibrational states, differences in excitation and pumping of the maser states may lead to different maser properties.

scholarly journals VLBI Observations of Turbulence in the Inner Solar Wind

1996 ◽  
Vol 154 ◽  
pp. 65-75
Author(s):  
Steven R. Spangler
Keyword(s):  
Solar Wind ◽  
Accurate Determination ◽  
The Sun ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Outer Corona ◽  
Very Long Baseline Array ◽  
Made In

AbstractI discuss the use of Very Long Baseline Interferometer (VLBI) phase scintillations to probe the conditions of plasma turbulence in the solar wind. Specific results from 5.0 and 8.4 GHz observations with the Very Long Baseline Array (VLBA) are shown. There are several advantages of phase scintillation measurements. They are sensitive to fluctuations on scales of hundreds to thousands of kilometers, much larger than those probed by IPS intensity scintillations. In addition, with the frequency versatility of the VLBA one can measure turbulence from the outer corona ~ 5 –10 R⊙ to well past the perihelion approach of the Helios spacecraft. This permits tests of the consistency of radio propagation and direct in-situ measurements of turbulence. Such a comparison is made in the present paper. Special attention is dedicated to measuring the dependence of the normalization coefficient of the density power spectrum, on distance from the sun. Our results are consistent with the contention published several years ago by Aaron Roberts, that there is insufficient turbulence close to the sun to account for the heating and acceleration of the solar wind. In addition, an accurate determination of the relationship could aid the detection of transients in the solar wind.

scholarly journals Very-long-baseline radio interferometry (VLBI) observations of gamma-ray blazars: results from millimeter-VLBI observations.

1995 ◽  
Vol 92 (25) ◽  
pp. 11377-11380 ◽  
Author(s):  
T. P. Krichbaum ◽  
S. Britzen ◽  
K. J. Standke ◽  
A. Witzel ◽  
C. J. Schalinski ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Radio Interferometry ◽  
Long Baseline ◽  
Vlbi Observations

scholarly journals VLBA observations of the 7mm SiO masers in TX Cam and R Cas

2002 ◽  
Vol 206 ◽  
pp. 274-277 ◽  
Author(s):  
Jiyune Yi ◽  
Roy S. Booth ◽  
John E. Conway ◽  
Anders Winnberg ◽  
Phillip J. Diamond
Keyword(s):  
High Resolution ◽  
Rotational Line ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Long Baseline ◽  
Mira Variables ◽  
Vlbi Observations ◽  
Vibrational Levels ◽  
Very Long Baseline Array ◽  
Made In

Simultaneous VLBI observations of the SiO masers of the J = 1 → 0 rotational line in the v = 1 and v = 2 vibrational levels toward Mira variables are presented. Because SiO maser lines are formed deep in circumstellar envelopes they serve as a unique tool to study the innermost envelopes of evolved stars. Although the first interpretation of SiO maser emission was made in 1974, observational features are only partially explained by models which have been suggested since then. Positional coincidence of the J = 1 → 0 masers of v = 1 and v = 2 has been argued as a way to distinguish among the maser pumping models, but it requires simultaneous observations of the two lines using high resolution. We have developed the technique for such observations during the last few years and here we report successful results of our simultaneous observations of the SiO v = 1 and v = 2 J = 1 → 0 masers using the Very Long Baseline Array (VLBA). We discuss the pumping mechanism in terms of our observational results.

scholarly journals AT 2018cow VLBI: no long-lived relativistic outflow

2019 ◽  
Vol 491 (4) ◽  
pp. 4735-4741 ◽  
Author(s):  
Michael F Bietenholz ◽  
Raffaella Margutti ◽  
Deanne Coppejans ◽  
Kate D Alexander ◽  
Megan Argo ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Expansion Velocity ◽  
X Ray ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Central Engine ◽  
Relativistic Jet ◽  
Symmetric Source ◽  
Fast Rise ◽  
Optical Transient

ABSTRACT We report on Very Long Baseline Interferometry (VLBI) observations of the fast and blue optical transient (FBOT), AT 2018cow. At ∼62 Mpc, AT 2018cow is the first relatively nearby FBOT. The nature of AT 2018cow is not clear, although various hypotheses from a tidal disruption event to different kinds of supernovae have been suggested. It had a very fast rise time (3.5 d) and an almost featureless blue spectrum, although high photospheric velocities (40 000 km s−1) were suggested early on. The X-ray luminosity was very high, ∼1.4 × 1043 erg s−1, larger than those of ordinary supernovae (SNe), and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived ‘central engine.’ It was also fairly radio luminous, with a peak 8.4-GHz spectral luminosity of ∼4 × 1028 erg s−1 Hz−1, allowing us to make VLBI observations at ages between 22 and 287 d. We do not resolve AT 2018cow. Assuming a circularly symmetric source, our observations constrain the average apparent expansion velocity to be ${\lt}0.49\, c$ by t = 98 d (3σ limit). We also constrain the proper motion of AT 2018cow to be ${\lt}0.51\, c$. Since the radio emission generally traces the fastest ejecta, our observations make the presence of a long-lived relativistic jet with a lifetime of more than 1 month very unlikely.

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 Very Long Baseline Interferometry Observations of the Proposed Radio Counterpart of an EGRET Source

Symmetry ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1516
Author(s):  
Patrik Milán Veres ◽  
Krisztina Éva Gabányi ◽  
Sándor Frey
Keyword(s):  
Very Long Baseline Interferometry ◽  
Gamma Ray ◽  
Interferometric Imaging ◽  
High Brightness ◽  
The Core ◽  
Long Baseline ◽  
Superluminal Motion ◽  
Γ Ray ◽  
Previous Claim ◽  
Jet Structure

We present high-resolution radio interferometric imaging observations of the radio source NVSS J182659+343113 (hereafter J1826+3431), the proposed radio counterpart of the γ-ray source, 3EG J1824+3441 detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory satellite. We analyzed eight epochs of archival multi-frequency very long baseline interferometry data. We imaged the asymmetric core–jet structure of the source, and detected apparent superluminal motion in the jet. At the highest observing frequency, 15.3 GHz, the core shows high brightness temperature indicating Doppler boosting. Additionally, the radio features undergo substantial flux density variability. These findings strengthen the previous claim of the association of the blazar J1826+3431 with the possible γ-ray source, 3EG J1824+3441.

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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