Modern design of the Irish nationalist "Sunburst flag".
Based on reports at crwflags.com, although in the designs shown there, the sun's rays are alternating between wavy and straight.
This design was spotted in Irish Republican marches in 2006.
An earlier version of the flag (early 20th century?) can be seen here.

"The Flagstaff flag, which is seen being raised in one of the scenes from the film 'Kick Any Stone', depicts a sunburst on a field of St. Patrick's, blue with the tips of sails emerging over the horizon."20th-century versions of the flag appear to have shown a half-sun "rising" either from the lower edge of the flag (1909) or from a cloud, in either a green or a blue field, or a full sun in the center of the flag, in a green field.[1]

But as it turns out, Wikipedia is in the real world, and this specific design, with the quarter-sun in the lower hoist corner and seven straight rays, originally posted to crwflags.com by Vincent Morley in 1997 and uploaded to Wikipedia in 2007, is now being sold as "the sunburst flag" on mugs and t-shirts.
Lexicon from the English Wikipedia
Vincent Morley, 23 March 1997, based on earlier designs going back to 1909 or 1858