Coordinate Algebras of Extended Affine Lie Algebras of Type A1

The cores of extended affine Lie algebras of reduced types were classified except for type A1. In this paper we determine the coordinate algebra of extended affine Lie algebras of type A1. It turns out that such an algebra is a unital n-graded Jordan algebra of a certain type, called a Jordan torus. We classify Jordan tori and get five types of Jordan tori.