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Register a new userThe complex gravitational lens system B1933+503
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We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat spectrum core (quadruply imaged) and two compact lobes symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object are detected. A redshift of 0.755 has been measured for the lens galaxy.
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The complex ten-component gravitational lens system B1933+503 has been monitored with the VLA during the period February to June 1998 with a view to measuring the time delay between the four compact components and hence to determine the Hubble parameter. Here we present the results of an `A configuration 8.4-GHz monitoring campaign which consists of 37 epochs with an average spacing of 2.8 days. The data have yielded light curves for the four flat-spectrum radio components (components 1, 3, 4 and 6). We observe only small flux density changes in the four flat-spectrum components which we do not believe are predominantly intrinsic to the source. Therefore the variations do not allow us to determine the independent time delays in this system. However, the data do allow us to accurately determine the flux density ratios between the four flat-spectrum components. These will prove important as modelling constraints and could prove crucial in future monitoring observations should these data show only a monotonic increase or decrease in the flux densities of the flat-spectrum components.
We report the discovery of the new gravitational lens system HE~0230$-$2130, a QSO at redshift $z=2.162$ consisting of at least five distinct components. Three of these are clearly lensed images of the QSO, one is most likely the lensing galaxy, while for the fifth component the identity is unclear: It could be a fourth QSO image (if so, then highly reddened), or another intervening galaxy, or a superposition of the two. Differential reddening seems to be important also for the first three QSO images. The surface density of faint galaxies near the QSO appears to be enhanced by a factor of $ga 2$, indicating the presence of a distant cluster close to the line of sight.
We report observations of the four-image gravitational lens system Q2237+0305 with the VLA at 20 cm and 3.6 cm. The quasar was detected at both frequencies (approx 0.7 mJy) with a flat spectrum. All four lensed images are clearly resolved at 3.6 cm, and the agreement of the radio and optical image positions is excellent. No radio emission is detected from the lensing galaxy, and any fifth lensed quasar image must be fainter than sim 20% of the A image flux density. Since the optical quasar images are variable and susceptible to extinction, radio flux ratios provide the best measurement of the macrolensing magnification ratios. The radio B/A and C/A image flux ratios are consistent with the observed range of optical variations, but the D/A ratio is consistently higher in the radio than in the optical. The radio ratios are consistent with magnification ratios predicted by lens models, and weaken alternative interpretations for Q2237+0305. More accurate radio ratios can distinguish between the models, as well as improve our understanding of both microlensing and extinction in this system.
We present hybrid maps of the A and B images of 0957+561 from each of four sessions of 6 cm VLBI observations that span the six-year interval 1987-1993. The inner- and outer-jets are clearly detected, and confirm the structures reported previously. There is no evidence of change in the separation between the core and inner-jet components, so the prospect of measuring the time delay using differential proper motions is not promising. The flux density in the core of each image peaked between 1989 and 1992. From the variation in these flux densities, we obtain a time-delay estimate of $sim$1 yr.
We report the discovery of a new two-image gravitational lens system from the Cosmic Lens All-Sky Survey, CLASS B2319+051. Radio imaging with the Very Large Array (VLA) and Multi-Element Radio-Linked Interferometer Network (MERLIN) shows two compact components with a flux density ratio of 5:1, separated by 1.36 arcsec. Observations with the Very Long Baseline Array (VLBA) resolve each of the radio components into a pair of parity-reversed subcomponents. Hubble Space Telescope (HST) observations with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) show a bright elliptical galaxy (G1) coincident with the radio position, and a second irregular galaxy (G2) 3.4 arcsec to the northwest. Previous spectroscopic studies have indicated that these galaxies are at different redshifts: z(G1) = 0.624, z(G2) = 0.588. Infrared counterparts to the lensed radio components are not detected in the NICMOS image, and the source redshift has not yet been determined. Preliminary mass modeling based on the VLBA subcomponent data indicates that the lensing potential includes a strong external shear contribution. A VLA monitoring program is currently being undertaken to measure the differential time delay.
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