Binary events and extragalactic planets in pixel microlensing

Pixel microlensing, i.e., gravitational microlensing of unresolved stars, can be used to explore distant stellar systems and, as a bonus, may be able to detect extragalactic planets. In these studies, binary lens events with multiple high-magnification peaks are crucial. Considering only those events that exhibit caustic crossings, we estimate the fractions of binary events in several pixel microlensing example surveys and compare them to the fraction of binary events in a classical survey with resolved stars. We find a considerable enhancement of the relative rate of binary events in pixel microlensing surveys relative to surveys with resolved sources. We calculate the rate distribution of binary events with respect to the time between caustic crossings. We consider possible surveys of M31 with ground-based telescopes and surveys of M87 with the Hubble Space Telescope and the Next Generation Space Telescope. For the latter, a pixel microlensing survey taking one image a day may observe on the order of 12 binary events per month.