Flach system of Jacquet-Langlands type and quaternionic period

In this article, we study the adjoint Selmer group of a modular form that admits a Jacquet-Langlands transfer to a modular form on a definite quaternion algebra. We show that this Selmer group has length given by the valuation of the Petersson norm of the quaternionic modular form. Our proof is based on an Euler system argument first used by Flach in his study for the adjoint Selmer group of an elliptic curve by producing elements in the motivic cohomology of the product of two Shimura curves. However our construction does not involve Siegel modular units which make it more adaptable to study adjoint motives coming from products of higher dimensional Shimura varieties.