I have always believed it to be pronounced as suggested above "Goch An" with a fairly hard "ch". However last year we had a weeks holiday in County Mayo Ireland in a rented cottage and to our surprise the owner turned out to be Dick Gaughan's cousin (Dick is half Scots, half Irish) the name Gaughan being Irish. To my ears he pronounced his name slightly softer than "Goch An" would suggest but then Dick has a Scottish accent !!!