Galactic Bulge Microlensing Optical Depth from EROS-2

Abstract

We present a new EROS-2 measurement of the microlensing optical depth toward the Galactic Bulge. Light curves of $5.6\times 10^6$ clump-giant stars distributed over $66\hat{A}{°}^2$ of the Bulge were monitored during seven Bulge seasons. 120 events were found with apparent amplifications greater than 1.6 and Einstein radius crossing times in the range $5 {\rm d}<t_\e <400 {\rm d}$. This is the largest existing sample of clump-giant events and the first to include northern Galactic fields. In the Galactic latitude range $1.4\degr<|b|<7.0\degr$, we find $\ddot{I}„/10^{-6}=(1.62\pm 0.23)\exp [-a(|b|-3\mathrm{deg})]$ with $a=(0.43\pm 0.16)\hat{A}{°}^{-1}$. These results are in good agreement with our previous measurement, with recent measurements of the MACHO and OGLE-II groups, and with predictions of Bulge models.

accepted A&A, minor revisions