Microlensing towards the LMC revisited by adopting a non-Gaussian velocity distribution for the sources

TL;DR

This study revisits microlensing predictions towards the LMC by using a non-Gaussian velocity distribution for sources, finding minimal impact on halo lensing estimates but a moderate increase in self-lensing predictions.

Contribution

It introduces a non-Gaussian velocity distribution for LMC sources into microlensing models, refining previous estimates and assessing the impact on MACHO-related parameters.

Findings

No change in halo microlensing rate or timescales with non-Gaussian velocities.

Moderate increase in self-lensing event rate and number with non-Gaussian velocities.

Error in MACHO mass and halo fraction estimates remains within 2%.

Abstract

We discuss whether the Gaussian is a reasonable approximation of the velocity distribution of stellar systems that are not spherically distributed. By using a non-Gaussian velocity distribution to describe the sources in the Large Magellanic Cloud (LMC), we reinvestigate the expected microlensing parameters of a lens population isotropically distributed either in the Milky Way halo or in the LMC (self lensing). We compare our estimates with the experimental results of the MACHO collaboration. An interesting result that emerges from our analysis is that, moving from the Gaussian to the non-Gaussian case, we do not observe any change in the form of the distribution curves describing the rate of microlensing events for lenses in the Galactic halo. The corresponding expected timescales and number of expected events also do not vary. Conversely, with respect to the self-lensing case, we observe a moderate increase in the rate and number of expected events. We conclude that the error in the estimate of the most likely value for the MACHO mass and the Galactic halo fraction in form of MACHOs, calculated with a Gaussian velocity distribution for the LMC sources, is not higher than 2%.