We perform a strong-lensing analysis of the merging galaxy cluster MACS J0416.1-2403 ( M0416 ; z = 0.42 ) in recent CLASH/HST observations .
We identify 70 new multiple images and candidates of 23 background sources in the range 0.7 \lesssim z _ { phot } \lesssim 6.14 including two probable high-redshift dropouts , revealing a highly elongated lens with axis ratio \simeq 5:1 , and a major axis of \sim 100 \arcsec ( z _ { s } \sim 2 ) .
Compared to other well-studied clusters , M0416 shows an enhanced lensing efficiency .
Although the critical area is not particularly large ( \simeq 0.6 ~ { } \square \arcmin ; z _ { s } \sim 2 ) , the number of multiple images , per critical area , is anomalously high .
We calculate that the observed elongation boosts the number of multiple images , per critical area , by a factor of \sim 2.5 \times , due to the increased ratio of the caustic area relative to the critical area .
Additionally , we find that the observed separation between the two main mass components enlarges the critical area by a factor of \sim 2 .
These geometrical effects can account for the high number ( density ) of multiple images observed .
We find in numerical simulations , that only \sim 4 \% of the clusters ( with M _ { vir } \geq 6 \times 10 ^ { 14 } h ^ { -1 } M _ { \odot } ) exhibit as elongated critical curves as M0416 .