Fℓ⁡(η,ρ)=(2⁢ℓ+1)!⁢Cℓ⁡(η)(-2⁢η)ℓ+1⁢((-2⁢η⁢ρ)1/2⁢J2⁢ℓ+1⁡((-8⁢η⁢ρ)1/2)+o⁡(|η|1/4)),