A Rapid Microlensing Event in the Q0957+561A, B Gravitational Lens System

We reanalyze brightness data sampled intensively over five nights at two epochs separated by the quasar lens time delay to examine the nature of the observed microlensing. We find strong evidence for a microlensing event with an amplitude of 1% and a timescale of 12 hr. The existence of such rapid microlensing, albeit at low amplitude, imposes constraints on the nature of the quasar and of the baryonic dark matter.