Pixel Lensing Search for Bright Microlensing Events and Variables in the Galactic Bulge

We describe a new method to search for gravitational microlensing toward theGalactic bulge that employs a small camera rather than a conventional telescopeand probes new regions of parameter space. The small aperture (~65 mm) permitsdetection of stellar flux variations corresponding to magnitudes 715. The large pixelsize (~10") and ~(6 deg)^2 field of view allows observation of the entire bulgewith a few pointings. With this large pixel size (and with the even larger 30"PSF that we advocate) most bulge stars are unresolved, so one is in the regimeof pixel lensing: microlensing and other forms of stellar variation aredetected from the difference of pixel counts in successive images. We identifythree principal uses of such a search. First, the observations are analogous tonormal pixel lensing observations of the bulge of M31, but are carried outunder conditions where the detected events can be followed up in detail. Thispermits crucial checks on the systematics of the M31 searches. Second, thesearch gives a complete inventory of bright bulge variables. Third, "extrememicrolensing events" (EMEs) can be found in real time. EMEs are events withmaximum magnifications A_max~200 which, if they were observed intensively fromtwo observatories, could yield the mass, distance, and speed of thegravitational lens. The instrumentation required to carry out the observationsis inexpensive. The observations could be made in parallel with existingmicrolensing searches and/or follow-up observations. The data reduction is muchsimpler than in ordinary pixel lensing because the PSF can be fixed by theoptics and so does not vary with atmospheric conditions.Comment: 12 pages, no figure