Pixel Lensing Experiment toward the M31 Bulge

Abstract

I demonstrate that one can detect pixel gravitational microlensing events at the rate $\sim 180\ {\rm events}\ {\rm yr}^{-1}$ and that some fraction of events ($\sim 15$) will be good enough to measure time scales at the $20\%$ level if the experiment is carried out toward the central M31 bulge region with a dedicated 1 m telescope and a $2{\rm K}\times2{\rm K}$ CCD. I also show that the event rate could be significantly increased (up to a factor 6.5) if more aggressive observation strategies are adopted. These aggressive strategies include multiple observation sites, using a bigger telescope, and reduction of seeing differences among images. A few years of observation could provide a data set big enough to extract important information about the M31 bulge such as the optical depth distribution, the mass spectrum of M31 MACHOs, and the luminosity function, which currently cannot be obtained by other methods. Additionally, I find that the extinction of M31 bulge light by dust in the disk is {\it not} important and can be approximated by the model in which only $20\%$ of light in $V$ band is extinguished over most of the bulge area.