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Full Idea
There is an 'objective', non-epistemic component to explanations, consisting of the things that must exist for A to be able to explain B, and the relations those things have to one another.
Clarification
'Epistemic' components concern how we know things
Gist of Idea
The objective component of explanations is the things that must exist for the explanation
Source
Alexander Bird (Philosophy of Science [1998], Ch.2)
Book Ref
Bird,Alexander: 'Philosophy of Science' [UCL Press 2000], p.64
A Reaction
There seems to be some question-begging here, in that you have to decide what explanation you are after before you can decide which existences are of interest. There are objective facts, though, about what causally links to what.