Circle

Let C1 be the circle of radius 1 with center at the origin. Let C2 be the circle of radius r with center at the point A=(4,1), where 1<r<3. Two distinct common tangents PQ and ST of C1 and C2 are drawn. The tangent PQ touches C1 at P and C2 at Q. The tangent ST touches C1 at S and C2 at T. Midpoints of the line segments PQ and ST are joined to form a line which meets the x-axis at a point B. If AB=√5, then the value of r2 is