[en] Measurement of the time delay between multiple images of a gravitational lens system is potentially an accurate method of determining the Hubble constant over cosmological distances. One of the most promising candidates for an application of this technique is the system B0218+357, which was found in the Jodrell Bank/VLA Astrometric Survey (JVAS). This system consists of two images of a compact radio source, separated by 335 milliarcsec, and an Einstein ring which can provide a strong constraint on the mass distribution in the lens. We present here the results of a three-month VLA monitoring campaign at two frequencies. The data are of high quality, and both images show clear variations in total flux density, percentage polarization and polarization position angle at both frequencies. The time delay between the variations in the two images has been calculated using a chi-squared minimization to be 10.5 +/- 0.4 d at 95 per cent confidence, with the error being derived from Monte Carlo simulations of the light curves. Although mass modelling of the system is at a preliminary stage, taking the lensing galaxy to be a singular isothermal ellipsoid and using the new value for the time delay, we obtain a value for the Hubble constant of 69^+13_-19 km s^-1 Mpc^-1, again at 95 per cent confidence.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Biggs, A. D.; University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL
Browne, I. W. A.; University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL
Helbig, Phillip ; University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL
Koopmans, L. V. E.; University of Groningen, Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, the Netherlands
Wilkinson, P. N.; University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL
Perley, R. A.; National Radio Astronomy Observatory, PO Box 0, Socorro, NM 87801, USA)
Language :
English
Title :
Time delay for the gravitational lens system B0218+357
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