@staticmethod
def alpha_r(r, sigma0, r_core):
    """
        radial deflection angle of the cored density profile

        :param r: radius (angular scale)
        :param sigma0: convergence in the core
        :param r_core: core radius
        :return: deflection angle
        """
    return 2 * sigma0 * r_core ** 2 / r * (1 - (1 + (r / r_core) ** 2) ** (
        -1.0 / 2))
