def _calc_specpp_loE(self, Egamma):
        """
        Delta-functional approximation for low energies Egamma < 0.1 TeV
        """
        from scipy.integrate import quad

        Egamma = Egamma.to("TeV").value
        Epimin = Egamma + self._m_pi ** 2 / (4 * Egamma)

        result = (
            2
            * quad(
                self._delta_integrand, Epimin, np.inf, epsrel=1e-3, epsabs=0
            )[0]
        )

        return result * u.Unit("1/(s TeV)")
Delta-functional approximation for low energies Egamma < 0.1 TeV