POINT-AGAPE pixel lensing survey of M31: Evidence for a MACHO contribution to galactic halos
/ Authors
S. C. Novati, S. Paulin-Henriksson, J. An, P. Baillon, V. Belokurov, B. Carr, M. Crézé, N. Evans, Y. Giraud-Héraud, A. Gould
and 15 more authors
P. Hewett, P. Jetzer, J. Kaplan, E. Kerins, S. Smartt, C. .. Stalin, Y. Tsapras, M. J. W. U. O. Zurich, Apc Paris, Cambridge University, Cern, U. O. London, U. Bretagne-Sud, O. University, L. Z. Q. U. Belfast
/ Abstract
The POINT-AGAPE collaboration is carrying out a search for gravitational microlensing toward M31 to reveal galactic dark matter in the form of MACHOs (Massive Astrophysical Compact Halo Objects) in the halos of the Milky Way and M31. A high-threshold analysis of 3 years of data yields 6 bright, short-duration microlensing events, which are confronted to a simulation of the observations and the analysis. The observed signal is much larger than expected from self lensing alone and we conclude, at the 95% confidence level, that at least 20% of the halo mass in the direction of M31 must be in the form of MACHOs if their average mass lies in the range 0.5-1 M⊙. This lower bound drops to 8% for MACHOs with masses � 0.01 M⊙. In addition, we discuss a likely binary microlensing candidate with caustic crossing. Its location, some 32' away from the centre of M31, supports our conclusion that we are detecting a MACHO signal in the direction of M31.
Journal: Astronomy and Astrophysics