Completed-Theses.md

@@ -13,6 +13,9 @@
 
 ### Master theses
 
+* *Simulation of the Optics of the Imaging Air-Cherenkov Telescope IceAct with Geant4*
+(Maurice Günder, April 2019, 3b)
+
 * *Analysis of Coincident Air Showers measured with IceCube, IceTop and IceAct during the Austral Winter 2016* 
 (Tobias Sälzer, September 2017, 3b)