Mathematics – Logic
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008mgm..conf.2591z&link_type=abstract
"THE ELEVENTH MARCEL GROSSMANN MEETING On Recent Developments in Theoretical and Experimental General Relativity, Gravitation an
Mathematics
Logic
Scientific paper
It is well-known that gravitational lensing is a powerful tool in the investigation of the distribution of matter, including that of dark matter (DM). Typical angular distances between images and typical time scales depend on the gravitational lens masses. For the of microlensing, angular distances between images or typical astrometric shifts are about 10-5 - 10-6 as. Such an angular resolution will be reached with the space-ground VLBI interferometer, Radioastron. It is known that in gravitationally lensed systems the probability (the optical depth) to observe microlensing is relatively high, therefore, for example, such gravitationally lensed objects, like CLASS gravitational lens B1600+434, look the most suitable to detect astrometric microlensing, since features of photometric microlensing have been detected in these objects. However, to directly resolve these images and to directly detect the apparent motion of the knots, the Radioastron sensitivity would have to be improved, since the estimated flux density is below the sensitivity threshold, alternatively, they may be observed by increasing an integration time, assuming that a radio source has a typical core - jet structure and microlensing phenomena are caused by the superluminal apparent motions of knots. In the case of a confirmation (or a disproval) of claims about microlensing in gravitational lens systems, one can speculate about the microlens contribution to the gravitational lens mass. The basic targets for microlensing searches should be bright point-like radio sources at cosmological distances. In this case, an analysis of their variability and a solid determination of microlensing could lead to an estimation of their cosmological mass density. Moreover, one could not exclude the possibility that non-baryonic dark matter could also form microlenses if the corresponding optical depth were high enough. Astrometric microlensing due Galactic MACHOs is not very important because of low optical depths and long typical time scales. Therefore, the launch of the space interferometer Radioastron will give excellent new facilities to investigate microlensing in the radio band, allowing the possibility not only to resolve microimages but also to observe astrometric microlensing.
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