2008A&A...479..903P


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.23CEST21:21:21

2008A&A...479..903P - Astronomy and Astrophysics, volume 479, 903-913 (2008/3-1)

The standing wave phenomenon in radio telescopes. Frequency modulation of the WSRT primary beam.

POPPING A. and BRAUN R.

Abstract (from CDS):

Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity, particularly when ``mosaicing'' over multiple telescope pointings. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for the primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Holographic observations, sampling angular scales between about 5-arcmin and 11-degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the main-lobe, near-in, and far-side-lobes out to a radius of more than 5-degrees was obtained. A robust empirical beam model was detemined in all polarization products (XX, XY, YX and YY) and at frequencies between 1322 and 1457MHz with 1MHz resolution. Substantial departures from axi-symmetry are apparent in the main-lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the main beam area, (2) the side-lobe to main-lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17MHz, consistent with the natural ``standing wave'' period of a 8.75m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for interferometric observations in complex fields, although at the expense of an increased computational load. The beam modulation with frequency can not be as easily overcome in total power observations. In that case it may prove effective to combat the underlying multi-path interference by coating all shadowed telescope surfaces with a broad-band isotropic scattering treatment.

Abstract Copyright:

Journal keyword(s): polarization - scattering - techniques: image processing - techniques: interferometric - techniques: spectroscopic - telescopes

CDS comments: Table 1, Fig. 9 In Simbad, source A = NVSS J082135+701429, source B = NVSS J082216+705308, source C = NVSS J082131+710755, source D = NVSS J082131+711943.

Simbad objects: 9

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Number of rows : 9

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 ICRF J054236.1+495107 Sy1 05 42 36.13789843 +49 51 07.2337251   18.45 17.80 17.210   ~ 1232 1
2 UGC 4305 IG 08 19 04.9878269182 +70 43 13.025604473 12.06 11.72 11.39 11.11   ~ 669 2
3 4C 71.06 Rad 08 21 31.00 +71 19 43.1           ~ 3 1
4 NVSS J082131+710755 Rad 08 21 31.40 +71 07 55.7           ~ 3 1
5 NVSS J082135+701429 Rad 08 21 35.50 +70 14 29.9           ~ 2 1
6 NVSS J082216+705308 Rad 08 22 16.86 +70 53 08.6           ~ 1 0
7 NGC 2841 LIN 09 22 02.655 +50 58 35.32 10.43 10.09 9.22     ~ 964 1
8 IC 2574 G 10 28 23.6204574649 +68 24 43.441365350 11.70 11.07 10.87 10.74   ~ 590 1
9 M 51 GiP 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 3683 4

    Equat.    Gal    SGal    Ecl

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2019.10.23-21:21:21

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