All Figures

$\begin{figure} \par\includegraphics[width=10cm,clip]{5145geom.eps} \end{figure}$ Figure 1: Synthesis-telecope geometry. Left: Antenna positions and feed orientations. Right: uv coverage.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{5145raw.eps} \end{figure}$ Figure 2: Cycle-1 dirty images, made with nominal instrumental corrections; left V, right $\vert\vec{p}\vert$ . Circles represent positions and fluxes of true sources (some being too weak to be shown), lines their linear polarization. Levels are to be compared with the peak source flux of 1. In the $\vert\vec{p}\vert$ image only one source can be identified; its high flux must be accidental, since the other $\vec{p}$ sources do not show up.
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In the text

$\begin{figure} \par\includegraphics[width=17.4cm,clip]{5145cyc2} \end{figure}$ Figure 3: Cycle-2 dirty images, corrected for instrumental errors fitted with the I-only Sky Model of cycle 1; left V, right $\vert\vec{p}\vert$ . Circles represent positions and fluxes of the true sources, lines their linear polarization. Note the difference in intensity scales whith Fig. 2. The peak levels of .002 in the V image and .025 in the $\vert\vec{p}\vert$ image are to be compared with the peak source flux of 1. Several polarized source now stand out; their fluxes are still too low by a factor 4 because polrotations at the successive hour angles are misaligned (cf. Sect. 6.3).
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In the text

$\begin{figure} \par\includegraphics[width=17.4cm,clip]{5145polC.eps} \end{figure}$ Figure 4: Poldeconversion. Shown are the differences of Q ( left) and I ( right) images after poldeconversion with those before. Circles mark the true source positions with areas proportional to intensity, bars indicate orientation and strength of true linear polarization. Note the flux scales. The Q image shows that poldeconversion has removed Q flux from every source. In the I image differences exist only where the source is truly polarized; positive and negative I differences reflect the bipolar nature of Q.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{5145pvCh.eps} \end{figure}$ Figure 5: Alignment of the linear polvectors observed at successive hour-angle intervals by self-alignment.
(a) Initially, the polvectors for successive hour angles are scattered in random directions by time-varying Faraday rotation. In the pre-calibrated image of cycle 1, their sum is much too small and badly misoriented. Most sources in the $\vec{p}$ images are drowned in scattered radiation due to instrumental errors (Fig. 2). We satisfy ourselves with making a Sky Model for I only.
(b) In the self-alignment of cycle 2, that Sky Model serving as reference provides no clue for the alignment of the observed polvectors; they are scattered once more, in random directions. Their sum is changed but remains weak. Yet, since gain and phase errors have been much reduced, the strongest polarized sources are now clearly identifiable (Fig. 3).
(c) The $\vec{p}_{{\rm lin}}$ flux in the Sky Model is now strong enough to serve as reference for aligning the observed $\vec{p}_{{\rm lin}}$ fluxes at the end of cycle 3. The polrotation of this reference is "frozen into'' the model (cf. Sect. 4.3.2). The polvectors for all hour angles are aligned to this reference with only very small errors left; $\vert\vec{p}_{{\rm lin}}\vert$ fluxes get close to their correct values.
(d) Further cycles will reduce the remaining errors at a level that is not visible on the scale of this diagram.
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In the text

$\begin{figure} \par\includegraphics[width=10cm,clip]{5145geom.eps} \end{figure}$	Figure 1: Synthesis-telecope geometry. Left: Antenna positions and feed orientations. Right: uv coverage.
Open with DEXTER