The Structure of the Gravitational Lens System B1152+199
P.G. Edwards , J.E.J. Lovell , H. Hirabayashi , D.L. Jauncey S. Toft, PASA, 18 (2), in press.

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Time Delay Determination

The results from three ``snap-shot'' observations are presented in Table 1. The quasar has not varied significantly over the three months spanned by these observations. It is interesting, however, to compare these flux densities with those from April 1998 (at 8.46GHz) of Myers et al. (1999): 52.27 and 17.23mJy. From the joint ATCA/VLA observations of PKS0405-385 (Jauncey et al. 2000), we expect absolute calibrations between the arrays to differ by a few percent at most, and not at the observed 10% level. The different resolutions are not the cause of the difference: the higher resolution (A-configuration) VLA observations have the higher component flux densities. These differences are suggestive of modest source variability over the two year interval between the observations, however no variation in the component flux densities was observed during an intensive monitoring campaign with the VLA in between June and November 1999 (Koopmans, private communication). We are attempting to quantify the differences in amplitude calibrations between the two arrays.

In addition to the component flux densities, we are able to determine fractional polarizations from the snapshot observations although the errors are naturally more appreciable. Variability in fractional polarization, without necessarily accompanying flux density variation, has been shown to be an alternative method of determining the time delay (Corbett et al. 1996; Biggs et al. 1999).

Experience with the PKS1830-211 system has emphasized the importance of identifying the starting epochs of flares and decays in the component light-curves, as these enable the time delay to be more tightly constrained (Lovell et al. 1998). Hence we are continuing our ATCA snap-shots at 6km array configurations, and supplementing this with observations in other configurations to monitor the total flux density. We planned initially to monitor the source at both 6.1 and 8.6GHz, however, we now consider it better to monitor solely at 8.6GHz with twice the original bandwidth, as this increases our sensitivity, gives better angular resolution, and we expect variations to be somewhat more pronounced at the higher frequency.

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Next Section: Lens Modelling
Title/Abstract Page: The Structure of the
Previous Section: Full-synthesis ATCA Image
Contents Page: Volume 18, Number 2

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© Copyright Astronomical Society of Australia 1997