Is it possible to repeat observations of gravitational lensing events?

[parallaxicality]

Or are they one-time data points?

[Noclevername]

If you know the relative motion of the lensing body, I don't see why repeating observations is not possible.

[Tom Mazanec]

That is a big if, I believe.

[Jens]

Or are they one-time data points?

You might need to be more clear by what you mean by an event. In my understanding, a lot of the gravitational lensing we see is between faraway galaxies, so you can observe them again and again if you want.

[antoniseb]

If you are talking about the events observed by OGLE and MACHO, the answer is that the event is observed once per site doing the observing. If you had observers spread across the solar system, you could get a few hours of variation in the peak time for each event, and possibly get some data about the diameter of the FWHM of the lens, and hence more data than we have now about the distance to the lensing body.

[ngc3314]

That effect is often known as lensing parallax, and has been observed between Earth and each of Spitzer, EPOXI, and Kepler. It is especially valuable to break the degeneracy between mass and transverse velocity of the lens. For typical events where both source and lens are stars in the Milky Way, the delay between locations a fraction of an AU apart is often several days (which works out from the numbers but I never expected intuitively).