Query : 2010A&A...515A..53M

2010A&A...515A..53M - Astronomy and Astrophysics, volume 515, A53-53 (2010/6-1)

Coherence loss in phase-referenced VLBI observations.


Abstract (from CDS):

Phase-referencing is a standard calibration technique in radio interferometry, particularly suited for the detection of weak sources close to the sensitivity limits of the interferometers. However, effects from a changing atmosphere and inaccuracies in the correlator model may affect the phase-referenced images, and lead to wrong estimates of source flux densities and positions. A systematic observational study of signal decoherence in phase-referencing and its effects in the image plane has not been performed yet. We systematically studied how the signal coherence in Very-Long-Baseline-Interferometry (VLBI) observations is affected by a phase-reference calibration at different frequencies and for different calibrator-to-target separations. The results obtained should be of interest for a correct interpretation of many phase-referenced observations with VLBI. We observed a set of 13 strong sources (the S5 polar cap sample) at 8.4 and 15GHz in phase-reference mode with 32 different calibrator/target combinations spanning angular separations between 1.5 and 20.5 degrees. We obtained phase-referenced images and studied how the dynamic range and peak flux-density depend on observing frequency and source separation. We obtained dynamic ranges and peak flux densities of the phase-referenced images as a function of frequency and separation from the calibrator. We compared our results with models and phenomenological equations previously reported. The dynamic range of the phase-referenced images is strongly limited by the atmosphere at all frequencies and for all source separations. The limiting dynamic range is inversely proportional to the sine of the calibrator-to-target separation. Not surpriseingly, we also find that the peak flux densities decrease with source separation, relative to those obtained from the self-calibrated images.

Abstract Copyright:

Journal keyword(s): techniques: interferometric - atmospheric effects - instrumentation: interferometers

Errata: + corrigendum vol. 533, p. C1 (2011)

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 8C 1150+812 QSO 11 53 12.4986308136 +80 58 29.152394328     18.5 18.54   ~ 227 1
2 8C 1803+784 BLL 18 00 45.6838528560 +78 28 04.018028016   16.4 16.4 15.46   ~ 705 1

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