Gℓ⁡(η,ρ)=-π⁢(-2⁢η)ℓ(2⁢ℓ+1)!⁢Cℓ⁡(η)⁢((-2⁢η⁢ρ)1/2⁢Y2⁢ℓ+1⁡((-8⁢η⁢ρ)1/2)+o⁡(|η|1/4)).