Baseline Radio Interferometer Research Articles

Space-ground radio interferometer RadioAstron

The paper considers the design, features, and characteristics of the Russian space-ground very long baseline radio interferometer (VLBRI) RadioAstron.

High resolution rapid response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)

Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of -30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at {\gamma}-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 15%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI.

A demonstration of precise calibration of tropospheric delay fluctuations with water vapor radiometers

The ability of water vapor radiometers (WVRs) to calibrate changes in tropospheric delay was demonstrated during very long baseline radio interferometer (VLBI) observations at Goldstone, California. WVR measurements reduced the observed VLBI delay variations over a 13 hr period by a factor of ≈2.5. When applied to shorter time scales, a ≈50% reduction in 100–700 s delay variations was achieved during conditions of high tropospheric activity. Thermal WVR noise precluded calibration of short time scale delay fluctuations during quiet tropospheric conditions.

Compact radio cores in Seyfert galaxies

view Abstract Citations (70) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Compact Radio Cores in Seyfert Galaxies Roy, A. L. ; Norris, R. P. ; Kesteven, M. J. ; Troup, E. R. ; Reynolds, J. E. Abstract We have observed a sample of 157 Seyfert galaxies with a 275 km baseline radio interferometer to search for compact, high brightness temperature radio emission from the active nucleus. We obtain the surprising result that compact radio cores are much more common in Seyfert 2 than in Seyfert 1 galaxies, which at first seems to be inconsistent with orientation unification schemes. We propose a model, involving optical depth effects in the narrow-line region, which can reconcile our result with the standard unified scheme. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174589 arXiv: arXiv:astro-ph/9404080 Bibcode: 1994ApJ...432..496R Keywords: Active Galactic Nuclei; Brightness Temperature; Radio Emission; Radio Sources (Astronomy); Seyfert Galaxies; Astronomical Models; Line Spectra; Optical Thickness; Radio Interferometers; Very Long Base Interferometry; Astrophysics; GALAXIES: ACTIVE; GALAXIES: NUCLEI; GALAXIES: SEYFERT; RADIO CONTINUUM: GALAXIES; Astrophysics E-Print: 21 pages and 7 figures, uuencoded tar-compressed postscript files, ATP189 full text sources arXiv | ADS | data products SIMBAD (159) NED (159)

A system for the coherent conversion of the signals of the centimeter-band astronomical very long baseline radio interferometer of the Scientific-Research Institute of Radiophysics

In the Scientific-Research Institute of Radiophysics we have developed specialized apparatus for the astronomical centimeter-band very long baseline radiointerferometer to solve a number of problems in astronomy, geodesy, and geodynamics [i]. The apparatus enables the main initial quantities (group delay and interference frequency) to be measured at the modern level of accuracy required. An important part of this apparatus is the system for the coherent conversion of the frequency of the received signals from the radio source. As is well known, this system can be constructed using an atc~nic frequency standard at each point of the very long baseline radio interferometer, the instability of which will determine the duration of the coherent storage of the interferometric signal. The problem reduces to transferring the highly stable properties of the signal of the frequency standard to the signals of the heterodynes, while ensuring their spectral purity. This is particularly important for an astronomical system for accurate and unambiguous measurements of interference frequency. In addition, the system for the coherent conversion of the signals of an astronomical very long baseline radio interferometer must carry out the conversion over a fairly broad frequency band, required to synthesize the corresponding broad effective frequency band, whose width to a large extent determines the final accuracy of the group-delav measurement [2]. i. Construction of the Centimeter-Band Coherent Signal Conversion System. The coherent signal conversion system we developed is a system with double freouency conversion with a receiving passband of 50 MHz, which converts the received centimeter-band signals into the operating band of the broadband frequency synthesis device (BFSD) of 30-76 MHz [3]. A block diagram of the system is shown in Fig. i. The signal of the first fixed-frequency heterodyne (FH) is generated directly from the 5-MHz signal from the Chi-69 rubidium frequency standard by multiplication, and the signal of the second heterodyne is obtained by multiplication of the output signal of a Ch6-58 frequency synthesizer, which is synchronized with the output signal of the same rubidium standard. The value of the second-heterodyne is set by the frequency synthesizer taking into account the previously calculated value of the differential Doppler frequency shift at the initial instant of each interferometer session of the observations of the space radio source. In existing very long base radio interferometer systems in the centimeter band, and some

Broadband synthesis in a very long baseline radiointerferometer

Broadband synthesis in a very long baseline radiointerferometer

The classical analysis of the response of a long baseline radio interferometer

Summary. A general derivation of the classical response of a long baseline interferometer is presented including the effects of finite bandwidth of the receiver systems, instrumental delays and phase shifts, instabilities in the separate local oscillators, as well as the effects of the retarded baseline. The general theory is then applied to a pair of antennae attached to the Earth and discussed in the light of a number of geophysical phenomena including the effects of precession, nutation, rotation, polar motion, annual aberration and Earth tides.

Radio‐wave deflection experiments confirm Einstein

Einstein yes, Brans–Dicke no, is the apparent verdict of some recent experiments at the National Radio Astronomy Observatory, Green Bank, West Virginia. Edward Fomalont and Richard Sramek measured the deflection of microwave radiation by the Sun's gravitational field and report results sufficiently precise that they are consistent with Einstein's general relativity but not with scalar–tensor formulations such as Brans–Dicke theory. The remaining uncertainty concerns possible systematic errors in these observations, not the formal statistical error, which appears to be sufficiently small. The experimenters used a 35‐km baseline radio interferometer to study three nearly collinear radio sources at two frequencies and found the bending to be 1.015±0.011 times that predicted by general relativity; the Brans–Dicke prediction differs by about seven percent.

Radio Telescopes Linked in Southern Hemisphere

Another long baseline radio interferometer is in operation, the first one in the southern hemisphere. The linkup (similar to those described in PHYSICS TODAY, November 1967, page 69) is between two NASA Deep Space Stations in Australia, one near Woomera in South Australia and one near Canberra in New South Wales. Its baseline is more than 9×106 wavelengths long at 2295 MHz. Preliminary observations of radio source 3C 273 show that the interferometer has an angular resolution better than 0.008 sec of arc.

A Three Base-line Tracking Radio Interferometer

ABSTRACT The experimental arrangement for a three baseline radio interferometer includes, as its main features, the orientation of the base lines in the plane and shape of an equilateral triangle, and the synchronous recording of the three interferograms of a transiting radio source, together with time and the amplitude-discriminated signal from a directional receiver. The sequence and the display of maxima and minima of each base-line pattern in relation to time will resolve the ambiguities of angular and scalar velocity of an orbiting object. The relative displacements of the central nulls and the secondary nulls of the recorded interferogram as compared against station time will resolve the ambiguities of the range vector. The directional ambiguity of the velocity vector of the object is resolved by an auxiliary radio receiving unit.