Fig. 3

Extraction of the refraction-induced structure from the naturally weighted 15.4 GHz VLBA images of 2023+335. The image on 2008 November 26 (top left) with the peak of 2.42 Jy beam-1 shows a typical parsec-scale morphology represented by a bright core and one-sided jet propagating along the PA ~ −20°. The image taken on 2009 May 28 (top middle) with a peak flux density of 2.62 Jy beam-1 shows an unusual brightness distribution, which is a result of multiple imaging of the source. The fitted Gaussian components are superposed on the images as shaded circles/ellipses. The difference image of the two epochs (top right) reveals a quasi-symmetric pattern dominated by two bright components and formed by refraction when the lens edge passes over the source. The pattern of de-magnified secondary images is extended nearly precisely along the line of constant galactic latitude, which is at PA ≈ 40° in this region of the sky (full line). All the images were convolved with an identical restoring beam, the FWHM of which is depicted as the crossed ellipse in the lower left corner. One milliarcsecond corresponds to about 3.5 pc. The total intensity profiles (bottom panel) are shown along the PA = 37° that connects the peaks of the refractive pattern in the difference image. The angular separation of the peaks is about 1 mas.
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