Detection of M31 Binaries via High-Cadence Pixel-Lensing Surveys

Abstract

The Angstrom Project is using a distributed network of two-meter class telescopes to conduct a high cadence pixel-lensing survey of the bulge of the Andromeda Galaxy (M31). With the expansion of global telescope network, the detection efficiency of pixel-lensing surveys is rapidly improving. In this paper, we estimate the detection rate of binary lens events expected from high-cadence pixel-lensing surveys toward M31 such as the Angstrom Project based on detailed simulation of events and application of realistic observational conditions. Under the conservative detection criteria that only high signal-to-noise caustic-crossing events with long enough durations between caustic crossings can be firmly identified as binary lens events, we estimate that the rate would be ${\Gamma }_{\mathrm{b}}\sim (7-15)f_{\mathrm{b}}(N/50)$ per season, where $f_{\mathrm{b}}$ is the fraction of binaries with projected separations of $10^{-3}\mathrm{AU}<\tilde{d}<10^3\mathrm{AU}$ out of all lenses and $N$ is the rate of stellar pixel-lensing events. We find that detected binaries would have mass ratios distributed over a wide range of $q\gtrsim 0.1$ but with separations populated within a narrow range of $1\mathrm{AU}\lesssim \tilde{d}\lesssim 5\mathrm{AU}$. Implementation of an alert system and subsequent follow-up observations would be important not only for the increase of the binary lens event rate but also for the characterization of lens matter.

arXiv comment6 pages, 4 figures

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• Exoplanetary searches with gravitational microlensing: polarization issues