Radio astrometry of the Cassini spacecraft with the very long baseline array

2016 ◽  
Author(s):  
Dayton L. Jones ◽  
Jonathan D. Romney ◽  
Vivek Dhawan ◽  
William M. Folkner ◽  
Robert A. Jacobson ◽  
...  
Keyword(s):  
Long Baseline ◽  
Very Long Baseline Array ◽  
Cassini Spacecraft

scholarly journals A radio parallax to the black hole X-ray binary MAXI J1820+070

2020 ◽  
Vol 493 (1) ◽  
pp. L81-L86 ◽  
Author(s):  
P Atri ◽  
J C A Miller-Jones ◽  
A Bahramian ◽  
R M Plotkin ◽  
A T Deller ◽  
...  
Keyword(s):  
Black Hole ◽  
Inclination Angle ◽  
Precise Measurement ◽  
Very Long Baseline Interferometry ◽  
X Ray ◽  
Long Baseline ◽  
Model Independent ◽  
Jet Velocity ◽  
Very Long Baseline Array

ABSTRACT Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network, we have made a precise measurement of the radio parallax of the black hole X-ray binary MAXI J1820+070, providing a model-independent distance to the source. Our parallax measurement of (0.348 ± 0.033) mas for MAXI J1820+070 translates to a distance of (2.96 ± 0.33) kpc. This distance implies that the source reached (15 ± 3) per cent of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity, and the mass of the black hole in MAXI J1820+070 to be (63 ± 3)°, (0.89 ± 0.09) c, and (9.2 ± 1.3) M⊙, respectively.

scholarly journals Multiepoch Very Long Baseline Array Observations of EGRET‐detected Quasars and BL Lacertae Objects: Connection between Superluminal Ejections and Gamma‐Ray Flares in Blazars

2001 ◽  
Vol 556 (2) ◽  
pp. 738-748 ◽  
Author(s):  
Svetlana G. Jorstad ◽  
Alan P. Marscher ◽  
John R. Mattox ◽  
Margo F. Aller ◽  
Hugh D. Aller ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
Long Baseline ◽  
Very Long Baseline Array

scholarly journals Very Long Baseline Array Astrometry of Cassini: The Final Epochs and an Improved Orbit of Saturn

2020 ◽  
Vol 159 (2) ◽  
pp. 72
Author(s):  
Dayton L. Jones ◽  
William M. Folkner ◽  
Robert A. Jacobson ◽  
Christopher S. Jacobs ◽  
Jonathan Romney ◽  
...  
Keyword(s):  
Long Baseline ◽  
Very Long Baseline Array

scholarly journals Water Masers Outburst in the Massive Stellar Cluster W49A

2015 ◽  
Vol 12 (S316) ◽  
pp. 155-156
Author(s):  
Busaba H. Kramer ◽  
Karl M. Menten ◽  
Tomasz Kamiński ◽  
Bo Zhang ◽  
Nimesh A. Patel ◽  
...  
Keyword(s):  
Stellar Cluster ◽  
Star Forming ◽  
Physical Conditions ◽  
Long Baseline ◽  
Major Flare ◽  
Multi Wavelength ◽  
Remarkable Result ◽  
Water Masers ◽  
Very Long Baseline Array ◽  
Very High

AbstractWe report a multi-wavelength study of a recent major flare (~ 80,000 Jy at VLSR ~ -98.1 km s−1) of the 22-GHz water maser in W49A. In February 2014, we started monthly monitoring with the Effelsberg 100-m radio telescope. In May 2014, we carried out the nearly simultaneous observations of the 22-GHz transition with selected submillimeter water transitions using the IRAM 30-m telescope (at 183 GHz) and the Atacama Pathfinder Experiment (APEX) 12-m telescope (from 321 to 475 GHz). We have also performed interferometric observations using the NRAO Very Long Baseline Array (VLBA) at 22 GHz and the Submillimeter Array (SMA) at 321 and 325 GHz. One remarkable result is the detection of very high velocity emission features in several transitions. Our data also represent its first detection of the 475-GHz water transition in a star-forming region. Studying these multiple masing transitions in conjunction with theoretical modeling of their excitation not only places strong constraints on the physical conditions of the masing gas but also allows us to study their association with the embedded massive stellar cluster in W49A.

scholarly journals Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales

2019 ◽  
Vol 628 ◽  
pp. A56 ◽  
Author(s):  
M. A. Keim ◽  
J. R. Callingham ◽  
H. J. A. Röttgering
Keyword(s):  
Magnetic Field ◽  
Spectral Characteristics ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
Spectrum Radio ◽  
Spectral Peaks ◽  
Murchison Widefield Array ◽  
Very Long Baseline Array ◽  
Field Strengths

Extragalactic peaked-spectrum radio sources are thought to be the progenitors of larger, radio-loud active galactic nuclei (AGN). Synchrotron self-absorption (SSA) has often been identified as the cause of their spectral peak. The identification of new megahertz-peaked spectrum sources from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey provides an opportunity to test how radio sources with spectral peaks below 1 GHz fit within this evolutionary picture. We observed six peaked-spectrum sources selected from the GLEAM survey, three that have spectral characteristics which violate SSA and three that have spectral peaks below 230 MHz, with the Very Long Baseline Array at 1.55 and 4.96 GHz. We present milliarcsecond resolution images of each source and constrain their morphology, linear size, luminosity, and magnetic field strength. Of the sources that are resolved by our study, the sources that violate SSA appear to be compact doubles, while the sources with peak frequencies below 230 MHz have core-jet features. We find that all of our sources are smaller than expected from SSA by factors of ≳20. We also find that component magnetic field strengths calculated from SSA are likely inaccurate, differing by factors of ≳5 from equipartition estimates. The calculated equipartition magnetic field strengths more closely resemble estimates from previously studied gigahertz-peaked spectrum sources. Exploring a model of the interaction between jets and the interstellar medium, we demonstrate that free-free absorption (FFA) can accurately describe the linear sizes and peak frequencies of our sources. Our findings support the theory that there is a fraction of peaked-spectrum sources whose spectral peaks are best modeled by FFA, implying our understanding of the early stages of radio AGN is incomplete.

scholarly journals Compact Cryogenic Receivers for the 1.3 to 43 GHz Range

1988 ◽  
Vol 129 ◽  
pp. 499-500
Author(s):  
S. Weinreb ◽  
R. Norrod ◽  
M. W. Pospieszalski
Keyword(s):  
High Electron Mobility Transistor ◽  
Low Noise ◽  
Current Status ◽  
High Electron ◽  
Light Weight ◽  
Closed Cycle ◽  
High Electron Mobility ◽  
Dual Channel ◽  
Long Baseline ◽  
Very Long Baseline Array

A series of front-ends utilizing small closed-cycle refrigerators and very low-noise, high-electron-mobility transistor (HEMT) amplifiers have been developed for use in the Very Long Baseline Array (VLBA). The frequency bands, amplifier noise temperatures, expected system temperatures, and current status are shown in Table I. The receivers are designed to be light weight (∼ 55 pounds except for 105 pounds at 1.5 GHz) for ease of installation and maintenance, are easily remotely controlled and monitored, and provide dual-channel circular polarization capability. Detailed descriptions of some of the front-ends are given in VLBA technical reports.

scholarly journals NGC 3894: a young radio galaxy seen by Fermi-LAT

2020 ◽  
Vol 635 ◽  
pp. A185 ◽  
Author(s):  
G. Principe ◽  
G. Migliori ◽  
T. J. Johnson ◽  
F. D’Ammando ◽  
M. Giroletti ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Radio Galaxies ◽  
High Energy ◽  
Apparent Velocity ◽  
Large Area ◽  
Long Baseline ◽  
Full Period ◽  
Very Long Baseline Array ◽  
High Energy Emission ◽  
First Time

Context. According to radiative models, radio galaxies may produce γ-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far. Aims. NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a γ-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the γ-ray and radio bands aimed at investigating its high-energy emission and assess its young nature. Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35years were used to study the radio morphology of NGC 3894 and its evolution. Results. NGC 3894 is detected in γ-rays with a significance >9σ over the full period, and no significant variability has been observed in the γ-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law (Γ = 2.0 ± 0.1) and a flux on the order of 2.2 × 10−9 ph cm−2 s−1. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be βapp, NW = 0.132 ± 0.004 and βapp, SE = 0.065 ± 0.003, respectively. Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59 ± 5 years. The estimated range of viewing angle (10° < θ <  21°) does not exclude a possible jet-like origin of the γ-ray emission.

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