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POINT-AGAPE Pixel Lensing Survey of M31 : Evidence for a MACHO contribution to Galactic Halos

By S. Calchi Novati, S. Paulin-Henriksson, J. An, P. Baillon, V. Belokurov, B.J. Carr, M. Creze, N.W. Evans, Y. Giraud-Héraud, A. Gould, Ph. Jetzer, J. Kaplan, E. Kerins, P. Hewett, S.J. Smartt, C.S. Stalin, Y. Tsapras and M.J. Weston

Abstract

The POINT-AGAPE CollaborationThe 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$_\odot$. This lower bound drops to 8% for MACHOs with masses $\sim 0.01$ M$_\odot$. 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

Topics: Galaxy: halo, M31: halo, lensing, dark matter, [PHYS.ASTR.CO] Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR.CO] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], [SDU.ASTR] Sciences of the Universe [physics]/Astrophysics [astro-ph]
Publisher: EDP Sciences
Year: 2005
DOI identifier: 10.1051/0004-6361:20053135
OAI identifier: oai:HAL:in2p3-00024518v1
Provided by: Hal-Diderot
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