Measuring the Remnant Mass Function of the Galactic Bulge

I show that by observing microlensing events both astrometrically andphotometrically, the Space Interferometry Mission (SIM) can measure the massfunction of stellar remnants in the Galactic bulge including white dwarfs,neutron stars, and black holes. Neutron stars and black holes can be identifiedindividually, while white dwarfs are detected statistically from the sharp peakin their mass function near M~ 0.6Msun. This peak is expected to be more thantwice as high as the `background' of main-sequence microlenses. I estimate thatof order 20% of the ~400 bulge microlensing events detected to date are due toremnants, but show that these are completely unrecognizable from their timescale distribution (the only observable that `normal' microlensing observationsproduce). To resolve the white-dwarf peak, the SIM mass measurements must beaccurate to ~5%, substantially better than is required to measure the massfunction of the more smoothly distributed main sequence. Nevertheless, SIMcould measure the masses of about 20 bulge remnants in 500 hours of observingtime.Comment: submitted to ApJ, 11 pages + 1 figur