Joachim Wambsganss, PASA, 18 (2), in press.
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Title/Abstract Page: Microlensing of Quasars
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Quasar Microlensing: Now and Forever?
Monitoring observations of various multiple quasar systems in the last decade have clearly established that the phenomenon of microlensing exists. There are uncorrelated variations in multiple quasar systems with amplitudes of more than a magnitude and time scales of weeks to months to years. However, in order to get close to a really quantitative understanding, much better monitoring programs need to be performed.On the theoretical side, there are two important questions: what do the lightcurves tell us about the lensing objects, and what can we learn from them about the size and structure of the quasar. As response to the first question, the numerical simulations are able to give a qualitative understanding of the measured lightcurves (detections and non-detections), in general consistent with ``conservative" assumptions about the object masses and velocities. But due to the large number of parameters (quasar size, masses of lensing objects, transverse velocity) and due to the large variety of lightcurve shapes, no satisfactory quantitative explanation or even prediction could be achieved. So far mostly ``limits" on certain parameters have been obtained. The prospects of getting much better lightcurves of multiple quasars, as shown by the OGLE collaboration, should be motivation enough to explore this quantitative direction in much more detail.
The question of the quasar structure deserves much more attention. Here gravitational lensing is in the unique situation to be able to explore an astrophysical field that is unattainable by any other means. Hence much more effort should be put into attacking this problem. This involves much more ambitious observing programs, with the goal to monitor caustic crossing events in many filters over the whole electromagnetic spectrum, and to further develop numerical techniques to obtain useful values for the quasar size and (one-dimensional) profile from unevenly sampled data in (not enough) different filters.
In relation to the ``early promises'' mentioned above, the future goals for quasar microlensing can be summarized as follows: 1) detect microlensing unambiguously in MORE gravitationally lensed systems 2) yes, determine the size of the continuum emitting regions of quasars, 3) microlensing is one of the very few tools that make it possible to determine the two-dimensional brightness profile of quasars: go for it! 4) determining masses and mass functions of compact (dark?) objects can make you famous and enrich the community. Applying the strategy of the groups involved in ``local microlensing'', and considering the potential of what we can learn about the lensed as well as the lensing objects, it is high time for better planned, organized and coordinated observing campaigns or even a dedicated telescope for quasar microlensing.
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Title/Abstract Page: Microlensing of Quasars
Previous Section: Unconventional Considerations on Quasar
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