I would like to know if the enchantment on Auriel's bow means that the sun damage is tripled, making it 60 sun damage, or is the bow damage tripled, making it unbelievably strong aginst undead.

I think it's the first but I just want to be sure

Sun damage.

Sun damage is tripled. If the bows damage was tripled I would have killed Harkon unbelievably fast.

The Bow's enchantment means that the Sun-hallowed Arrows to triple their normal beastly damage to undead.

If you want a fun experiment with how much damage they can possibly do, hit a Draugr Deathlord with one. It's pretty spectacular...

Ok that's what I thought, I just wanted to make sure It wasn't a super weapon