I take it if it had been THE official newspaper, the sentence would be Is é an nuachtán oifigiúil é then?
Exactly. Or, if you wanted to stress 'it': is eisean an nuachtán oifigiúil. Or it could change other ways to stress other things.
So.. you can't have an 'an' next to an 'is'? Trying to make sense of some information in the comments of this exact sentence with 'the' in it I saw previously.