Yes a hole made by Mangus, when he left said hole is source of all magic.
Well by that logic at night magic should be weaker since moonlight is just the suns light reflected.
It also doesn't make sense that vamps all use magic, yet have a weakness, aversion where the sun is concerned, that should make them weaker in magic not all magic users.
I think this lore needs work.
Kinda like a pagan Roman emporer helping to chose which books would end up in a Christian bible and which would become gnostic.