Microlensing in the Small Magellanic Cloud: lessons from an N-body simulation

We analyse an N-body simulation of the Small Magellanic Cloud (SMC), that o f Gardiner & Noguchi, to determine its microlensing statistics. We find tha t the optical depth owing to self-lensing in the simulation is low, 0.4 X 1 0(-7), but still consistent (at the 90 per cent level) with that observed b y the EROS and MACHO collaborations, This low optical depth is due to the r elatively small line-of-sight thickness of the SMC produced in the simulati on. The proper motions and time-scales of the simulation are consistent wit h those observed assuming a standard mass function for stars in the SMC, Th e time-scale distribution from the standard mass function generates a signi ficant fraction of short time-scale events: future self-lensing events towa rds the SMC may have the same time-scales as events observed towards the La rge Magellanic Cloud (LMC), Although some debris was stripped from the SMC during its collision with the LMC about 2 x 10(8) yr ago, the optical depth of the LMC owing to this debris is low, a few x 10(-9), and thus cannot ex plain the measured optical depth towards the LMC.