Kavli Affiliate: Paul L. Schechter
| First 5 Authors: Luke Weisenbach, Timo Anguita, Jordi Miralda-Escudé, Masamune Oguri, Prasenjit Saha
| Summary:
Microlensing near macro-caustics is a complex phenomenon in which swarms of
micro-images produced by micro-caustics form on both sides of a macro-critical
curve. Recent discoveries of highly magnified images of individual stars in
massive galaxy cluster lenses, predicted to be formed by these micro-image
swarms, have stimulated studies on this topic. In this Chapter, we explore
microlensing near macro-caustics using both simulations and analytic
calculations. We show that the mean total magnification of the micro-image
swarms follows that of an extended source in the absence of microlensing.
Micro-caustics join into a connected network in a region around the
macro-critical line of a width proportional to the surface density of
microlenses; within this region, the increase of the mean magnification toward
the macro-caustic is driven by the increase of the number of micro-images
rather than individual magnifications of micro-images. The maximum achievable
magnification in micro-caustic crossings decreases with the mass fraction in
microlenses. We conclude with a review of applications of this microlensing
phenomenon, including limits to the fraction of dark matter in compact objects,
and searches of Population III stars and dark matter subhalos. We argue that
the discovered highly magnified stars at cosmological distances already imply
that less than $sim$ 10% of the dark matter may be in the form of compact
objects with mass above $sim 10^{-6}, M_{odot}$.
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