[astro-ph/0504188] POINT-AGAPE Pixel Lensing Survey of M31 : Evidence for a MACHO contribution to Galactic Halos

Authors:  S. Calchi Novati (1), S. Paulin-Henriksson (2), J. An (3), P. Baillon (4), V. Belokurov (3), B.J. Carr (5), M. Creze (2,6), N.W. Evans (3), Y. Giraud-Heraud (2), A. Gould (7), Ph. Jetzer (1), J. Kaplan (2), E. Kerins (8), P. Hewett (3), S.J.
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$_\odot$. 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.
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Garth Antony Barber
Posts: 59
Joined: July 19 2005
Affiliation: Published independent

[astro-ph/0504188] POINT-AGAPE Pixel Lensing Survey of M31 :

Post by Garth Antony Barber » July 21 2005

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

Five micro-lensing events detected in survey of regions around M31. They were modelled by a Monte-Carlo scheme in which lensing masses in the range 0.1 M_\odot and [0.5 - 1]M_\odot.

My question, probing whether a component of DM might be BHs, is: "Could these events actually be detections of much larger masses (e.g. IMBHs of a mass range [10^2 - 10^4]M_\odot)?"

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