The central regions of the gravitationally lensed quasar Q2237+0305 can be indirectly resolved on nano-arcsecond scales if viewed spectrophotometrically during a microlensing high magnification event ( HME ) .
Q2237+0305 is currently being monitored from the ground ( eg .
OGLE collaboration , Apache Point Observatory ) , with the goal , among others , of triggering ground and spacecraft based target of opportunity ( TOO ) observations of such an HME .
In this work we investigate the rate of change ( trigger ) in image brightness that signals an imminent HME and importantly , the separation between the trigger and the event peak .
In addition , we produce colour dependent model light-curves by combining high-resolution microlensing simulations with a realistic model for a thermal accretion disc source .
We make hypothetical target of opportunity spectroscopic observations using our determination of the appropriate trigger as a guide .
We find that if the source spectrum varies with source radius , a 3 observation TOO program should be able to observe a microlensing change in the continuum slope following a light-curve trigger with a success rate of \ga 80 \% .