In this article, we created a well-resolved aftershock catalog for the 2015 Gorkha earthquake in Nepal by processing 11 months of continuous data using an automatic onset and hypocenter determination procedure. Aftershocks were detected by the NAMASTE temporary seismic network that is densely distributed covering the rupture area and became fully operational about 50 days after the mainshock. The catalog was refined using a joint hypocenter determination technique and an optimal 1D velocity model with station correction factors determined simultaneously. We found around 15,000 aftershocks with the magnitude of completeness of M-L 2. Our catalog shows that there are two large aftershock clusters along the north side of the Gorkha-Pokhara anticlinorium and smaller shallow aftershock clusters in the south. The patterns of aftershock distribution in the northern and southern clusters reflect the complex geometry of the Main Himalayan thrust. The aftershocks are located both on the slip surface and through the entire hanging wall. The 1D velocity structure obtained from this study is almost constant at a P-wave velocity (V-P) of 6.0 km/s for a depth of 0-20 km, similar to V-P of the shallow continental crust.