Contributions of Ṗ_b from differential Galactic acceleration and the Shklovskii effect as a function of the distance to the pulsar (see text for details). The orange and blue areas indicate the 1-σ confidence of these two effects. The solid lines represent the nominal values, and the dotted curves are the ±1-σ uncertainties. The total external contribution of Ṗ_b is shown by the corresponding red area and curves. The uncertainties come from the uncertainty of R₀, Θ₀ and the proper motion. The dashed red and black lines are the distances derived from YMW16 and NE2001. The grey area displays ΔṖ_b = Ṗ_b,obs − Ṗ_b,GR. This quantity, estimated in detail in Sect. 4.1, represents a measurement of the total external contribution that assumes the validity of GR; its width represents its uncertainty, which is dominated by the error of the observed Ṗ_b.