Astron. Astrophys. 333, 893-896 (1998)

2. Point-mass lens and point source

For a lens at a distance from the observer, a source at a distance from the observer, and the lens-source distance, the Einstein radius for a lens of mass M is given by

Let the lens move on a straight line with a velocity transverse to the line-of-sight observer-source, so that it moves one Einstein radius in the lens plane in the time . ¹ Let denote the time at the closest approach and the impact parameter at in units of Einstein radii. For the impact parameter at time t one obtains

where

The light amplification for a point source and a point-mass lens is given by

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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