There came to the beach, a poor exile of Erin,
The dew on his thin robe was heavy and chill,
For his country he sighed, when at twilight repairing,
To wander alone by the wind beaten hill.
But the day-star attracted his eyes' sad devotion,
For it rose o'er his own native isle of the ocean,
Where once in the fire of his youthful emotion,
He sang the bold anthem of Erin Go Bragh.

From 'The Exile of Erin' by Glasgow-born Thomas Campbell (1777-1844).
(Campbell also wrote'Hohenlinden', and, 'Lord Ullin's Daughter').

Campbell's poetry was very popular in Victorian and Edwardian times and Kearney was a voracious reader. However I have no idea if this is what Gaughan is referring to.

I suspect that Kearney probably did read the poem and that he picked up the term, 'Erin go bragh' from it. Other than those three words, I see little similarity between the two. His main 'source' was, I believe, from within his own head.

With other of his songs, this was not so: e.g. 'The Three-Coloured Ribbon'.