Exploration of Source Frequency Phase Referencing Techniques for Astrometry and Observations of Weak Sources with High Frequency Space Very Long Baseline Interferometry (original) (raw)
Related papers
2011
Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospect of achieving the highest angular resolutions and astrometric accuracies, resulting from the long baselines between ground and satellite telescopes. Nevertheless, space-specific issues, such as limited accuracy in the satellite orbit reconstruction and constraints on the satellite antenna pointing operations, limit the application of conventional phase referencing. We investigate the feasibility of an alternative technique, source frequency phase referencing (SFPR), to the S-VLBI domain. With these investigations we aim to contribute to the design of the next-generation of S-VLBI missions. We have used both analytical and simulation studies to characterize the performance of SFPR in S-VLBI observations, applied to astrometry and increased coherence time, and compared these to results obtained using conventional phase referencing. The observing configurations use the specifications of t...
In this document we layout a new method to achieve "bona fide" high precision Very-Long-Baseline-Interferometry (VLBI) astrometric measurements of frequency-dependent positions of celestial sources (even) in the high (mm-wavelength) frequency range, where conventional phase referencing techniques fail. Our method, dubbed "Source/Frequency Phase Referencing" (SFPR) combines fast frequency-switching (or dual-frequency observations) with the source switching of conventional phase referencing techniques. The former is used to calibrate the dominant highly unpredictable rapid atmospheric fluctuations, which arise from variations of the water vapor content in the troposphere, and ultimately limit the application of conventional phase referencing techniques; the latter compensates the slower time scale remaining ionospheric/instrumental, non-negligible, phase variations. For cm-VLBI, the SFPR method is equivalent to conventional phase referencing applied to the measurem...
arXiv: Instrumentation and Methods for Astrophysics, 2009
In this document we layout a new method to achieve "bona fide" high precision Very-Long-Baseline-Interferometry (VLBI) astrometric measurements of frequency-dependent positions of celestial sources (even) in the high (mm-wavelength) frequency range, where conventional phase referencing techniques fail. Our method, dubbed "Source/Frequency Phase Referencing" (SFPR) combines fast frequency-switching (or dual-frequency observations) with the source switching of conventional phase referencing techniques. The former is used to calibrate the dominant highly unpredictable rapid atmospheric fluctuations, which arise from variations of the water vapor content in the troposphere, and ultimately limit the application of conventional phase referencing techniques; the latter compensates the slower time scale remaining ionospheric/instrumental, non-negligible, phase variations. For cm-VLBI, the SFPR method is equivalent to conventional phase referencing applied to the measurem...
MultiView High Precision VLBI Astrometry at Low Frequencies
The Astronomical Journal, 2017
The arrival of the Square Kilometer Array (SKA) will revitalise all aspects of Very Long Baseline Interferometry (VLBI) astronomy at the lower frequencies. In the last decade there have been huge strides towards routinely achieving high precision VLBI astrometry at frequencies dominated by the tropospheric contributions, most notably at 22GHz, using advanced phase referencing techniques. Nevertheless to increase the capability for high precision astrometric measurements at low radio frequencies (<8 GHz) an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. Observations at low frequencies are dominated by distinct direction dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase referencing calibrator. The MultiView technique holds the key to the compensation of atmospheric spatial-structure errors, by using observations of multiple calibrators and 2-D interpolation. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phasereferencing techniques.
2009
This document describes the advantages of applying source/frequency phase referencing (sfpr) techniques to the analysis of VLBI observations with VSOP-2, for high precision astrometric measurements and/or increased sensitivity. The sfpr calibration technique basics and a demonstration of the method applied to highest frequency VLBA observations are described in detail in VLBA Scientific Memo 31. Here we outline its importance in the context of space VLBI astrometry with VSOP-2, where errors in the satellite orbit determination and rapid tropospheric phase fluctuations set extreme challenges for the successful application of conventional phase referencing techniques, specially at the higher frequencies. sfpr is ideally suited for full calibration of those-regardless of the orbit determination accuracy-and, in general, of any non-dispersive terms. The requirements for application of sfpr techniques are fully compatible with current technical specifications of VSOP-2. Hence we foresee that sfpr will play an important role in helping expanding the scientific outcome of the space VLBI mission.
1 High Precision Astrometric Millimeter VLBI Using a New Method for Atmospheric Calibration
2016
We describe a new method which achieves high precision Very Long Baseline Interferometry (VLBI) astrometry in observations at millimeter wavelengths. It combines fast frequency-switching observations, to correct for the dominant nondispersive tropospheric fluctuations, with slow source-switching observations, for the remaining ionospheric dispersive terms. We call this method Source-Frequency Phase Referencing. Provided that the switching cycles match the properties of the propagation media, one can recover the source astrometry. We present an analytic description of the two-step calibration strategy, along with an error analysis to characterize its performance. Also, we provide observational demonstrations of a successful application with observations using the Very Long Baseline Array at 86 GHz of the pairs of sources 3C274 & 3C273 and 1308+326 & 1308+328, under various conditions. We conclude that this method is widely applicable to millimeter VLBI observations of many target sources, and unique in providing bona-fide astrometrically registered images and high precision relative astrometric measurements in mm-VLBI using existing and newly built instruments.
Multi-beam capabilities for high precision astrometry at low frequencies using VLBI
… at http://pos. sissa. it/cgi …, 2010
We are carrying out a simulation study to characterise the advantages of VLBI with multiple beams, which will be a feature of the next generation of instruments. We will focus on VLBI astrometric measurements at lower frequencies (1.4 GHz and below). For our simulations, we have selected a network consisting of ASKAP, the Australian SKA precursor, plus existing Australian antennas from the LBA (Long Baseline Array) and the new antenna in New Zealand (figure 1a). We have used different models to represent the ionospheric turbulences and frequencies. The preliminary results show an improvement of an order of magnitude in the astrometric precision achieved using multiple calibrators with angular separations of a few degrees around the target, with respect to a single nearby (1 • away) calibrator. Such astrometric precision is comparable to using in-beam phase referencing with a calibrator some arcminutes away. We plan to expand our simulations to include other networks with multi-beam capability, and ultimately SKA-like configurations.
The application of MultiView Methods for High Precision Astrometric Space VLBI at Low Frequencies
2013
High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the conventional frequency range, i.e. 20cm, is a requirement for a number of high priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in Pulsar--Black Hole pairs and OH masers anywhere in the Milky Way Galaxy and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8m in size and with ionospheric atmospheres consistant with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high quality orbit reconstruction ...
The Astronomical Journal, 2011
We describe a new method which achieves high-precision very long baseline interferometry (VLBI) astrometry in observations at millimeter (mm) wavelengths. It combines fast frequency-switching observations, to correct for the dominant non-dispersive tropospheric fluctuations, with slow source-switching observations, for the remaining ionospheric dispersive terms. We call this method source-frequency phase referencing. Provided that the switching cycles match the properties of the propagation media, one can recover the source astrometry. We present an analytic description of the two-step calibration strategy, along with an error analysis to characterize its performance. Also, we provide observational demonstrations of a successful application with observations using the Very Long Baseline Array at 86 GHz of the pairs of sources 3C274 and 3C273 and 1308+326 and 1308+328 under various conditions. We conclude that this method is widely applicable to mm-VLBI observations of many target sources, and unique in providing bona fide astrometrically registered images and high-precision relative astrometric measurements in mm-VLBI using existing and newly built instruments, including space VLBI.