tokens: values at the reference epoch at which the two timing models of Table 4 are defined, MJD 55655. The fit to the position at the median MJD of each aeon (the finely dotted orange line) returns μ α = 5.63 ± 0.10 mas yr − 1 and μ δ = 2.34 ± 0.28 mas yr − 1 while the dashed lilac line represents the values obtained from the BTX model, shown in Table 4 . Using an estimated distance of ≃1040 pc (from the NE2001 model of free-electron distribution in the Galaxy; Cordes Lazio 2003 ) and a total proper motion , a 2D transverse velocity of ν t = 30 ± 9 km s − 1 was calculated. This assumes an uncertainty of 30 per cent 4 in the DM-derived distance mentioned above. The measurement is in agreement with the value of 30 ± 20 km s − 1 measured by Stappers et al. ( 1998 ) and represents a twofold increase in precision, even though the uncertainty of the DM-derived distance is assumed to be much greater. It should be noted that this is significantly lower than the average value of 93 ± 13 km s − 1 reported in Desvignes et al. ( 2016 ) for the transverse velocities of binary MSPs. However, it agrees well with the value of 56 ± 3 km s − 1 reported for the binary MSPs with distance measurements from parallaxes. The proper motion values obtained from the BTX model appear to be inconsistent with those obtained from fitting to position measurements for every aeon using the respective ELL1 models. This is because the proper motion terms and the OFDs are strongly covariant and therefore the uncertainties in the values obtained from the BTX model are heavily underestimated, reinforcing the need for cautious usage of this model. 3.2 DM variations Since the DM is a measure of the density of the ionized interstellar medium (IISM) along the line of sight to the pulsar, both the motion of the pulsar and the dynamical evolution of the IISM affect this value. While it is possible to obtain the DM from timing, ‘JUMPS’ or instrumental offsets introduced to align the ToAs from the different backends are fully covariant with the DM and prevent an accurate measurement directly from the data set presented above. Therefore, a DM value of 20.7299(17) cm − 3 pc is adopted from the LOFAR measurements of Kondratiev et al. ( 2016 ). When simultaneous dual (or multi-) frequency observations are available, it is, however, possible to accurately estimate the variation in the DM. The WSRT PuMa-II backend provides observations centred at 345 and 1380 MHz, with a cadence of roughly three weeks. Observations between the two frequencies are sequential, which are separated by, at most, a few days and available for the MJD range ∼54600–56800. Since low-frequency observations are more sensitive to the DM variations, these are utilized to measure them instead of the two frequency-band observations of the PSRIX backend. To measure DM variations, the PuMa-II ToAs were fitted for DM using the ELL1 model presented in Table 4 . The ToAs were then split into 100 d long intervals, to ensure that enough
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