Comparison of the resulting spectra of pp interaction in the part of the SNR shock transporting into dense clouds with the observed γ-ray flux points for the SNR W44 (χ²/dof = 3.2). The dashed line represents the spectrum not take into the ion–neutral damping account. The parameters are n₁ = 120 cm⁻³, T₁ = 10² K, B₁ = 10 μG, x₀ = 1 pc, η = 0.4, d = 2.9 kpc with u₁ = 35 km s⁻¹. The average emitting volume is normalized by making the resulting flux consistent with the detected one with the Fermi LAT, and the data points are from Ackermann et al. (2013).