The find is an 80m diameter double banked henge. It has been known about for a while (one of the opposition groups told the National Museum about it) and is just 100m or so from Rath Lugh. It's been heavily ploughed out and so was only just visible. The initial survey mis-identified it, but the arhaeos have been digging it for a while and have now identified it properly.
Source: Irish Times
The only known Irish henges that are bigger are on Tara itself. I don't know of any double-banked henges anywhere .... (?)