Stars within the Large Magellanic Cloud as potential lenses for observed microlensing events

Abstract

Massive Compact objects in the halo, known as MACHOs, have been postulated as the origin of a substantial fraction of `dark matter' known to exist in the haloes of galaxies$^{1,2}$. Paczy\'nski$^3$ has suggested that it might possible to detect these low-luminosity objects by their potential to act as gravitational lenses, causing a characteristic brightening when they cross the path of light from a star in a nearby galaxy. very recently, two groups reported possible detections of microlensing of stars in the Large Magellanic Cloud (LMC)$^{4,5}$. Here I show that microlensing by stars within the LMC itself can account for the observed events. It is further shown that if stars within the LMC are the lenses, the observed light curve can differ from the light curve due to a galactic lens even at relatively low magnifications. This provides a possibility of distinguishing between the galactic lenses and the LMC lenses. For a given number of monitored stars, the LMC induced events should be strongly concentrated towards the central region of the LMC, while the galactic events should be uniformly spread over the whole area of the LMC, so the two can also be distinguished statistically.