Let the tangents at the points $A ( 4 , - 11 )$ and $B ( 8 , - 5 )$ on the circle $x ^ { 2 } + y ^ { 2 } - 3 x + 10 y - 15 = 0$, intersect at the point $C$. Then the radius of the circle, whose centre is $C$ and the line joining $A$ and $B$ is its tangent, is equal to\\
(1) $\frac { 3 \sqrt { 3 } } { 4 }$\\
(2) $2 \sqrt { 13 }$\\
(3) $\sqrt { 13 }$\\
(4) $\frac { 2 \sqrt { 13 } } { 3 }$