In the $xy$-plane, a circle has center $C$ with coordinates $(h,k)$. Points $A$ and $B$ lie on the circle, and $\angle ACB$ is a right angle. The length of $\overline{AB}$ is $\sqrt{98}$. If point $A$ has coordinates $(h+x,k+y)$, what is the value of $x^2+y^2$?