MONTE-CARLO SIMULATIONS OF MACHO PARALLAXES FROM A SATELLITE

Three ongoing microlensing experiments have found more candidate event s than expected from the known stars. These experiments measure only o ne parameter of the massive compact halo objects (MACHOs), the magnifi cation timescale of the events. More information is required to unders tand the nature of the MACHOs. A satellite experiment has been propose d to measure their projected transverse speed (v) over tilde = v/(1 - z), where v is the MACHO transverse speed and z is its distance divide d by the distance of the source. Measurement of (v) over tilde would d etermine whether the MACHOs were in the Galactic disk, Galactic halo, or in the Large Magellanic Cloud (LMC). We simulate events observed to ward the LMC by the Earth and by a satellite in an Earth-like heliocen tric orbit. To leading order, such an experiment determines (v) over t ilde up to a twofold degeneracy. More precise measurements break the d egeneracy. We show that with photometric precisions of 3%-4% and appro ximately one observation per day, (v) over tilde can be measured with a maximum error of 20% for 70%-90% of events similar to the ones repor ted by the EROS and MACHO collaborations. The projected transverse vel ocity is known with the same maximum error for 60%-75% of these events . This 20% maximum error is not a 1 sigma error but is mostly due to d egeneracy between two possible solutions, each one being localized to much better than 20%. These results are obtained with an Earth-satelli te separation of 1 AU. For larger separations, the result improve sign ificantly for masses M greater than or similar to 0.1 M. and worsen so mewhat for masses M less than or similar to 0.1 M..