VLBI phase-reference observations of the gravitational lens JVAS B0218+357
Abstract
We present the results of phase-referenced VLBA+Effelsberg observations at five frequencies of the double-image gravitational lens JVAS B0218+357, made to establish the precise registration of the A and B lensed image positions. The motivation behind these observations is to investigate the anomalous variation of the image flux density ratio (A/B) with frequency - this ratio changes by almost a factor of two over a frequency range from 1.65 GHz to 15.35 GHz. We investigate whether frequency dependent image positions, combined with a magnification gradient across the image field, could give rise to the anomaly. Our observations confirm the variation of image flux ratio with frequency. The results from our phase-reference astrometry, taken together with the lens mass model of Wucknitz et al. (2004), show that shifts of the image peaks and centroids are too small to account for the observed frequency-dependent ratio.
Keywords
Cite
@article{arxiv.astro-ph/0508198,
title = {VLBI phase-reference observations of the gravitational lens JVAS B0218+357},
author = {Rupal Mittal and Richard Porcas and Olaf Wucknitz and Andy Biggs and Ian Browne},
journal= {arXiv preprint arXiv:astro-ph/0508198},
year = {2009}
}
Comments
10 pages, 8 figures, accepted by A&A