Pulsar's position, proper motion and parallax are important parameters in timing equations. It is a really challenging work to fit astrometric parameters accurately through pulsar timing, especially for pulsars that show irregular timing properties. As the fast development of related techniques, it is possible to measure astrometric parameters of more and more pulsars in a model$\textrm{-}$independent manner with the Very Long Baseline Interferometry (VLBI). In this work, we select 16 normal pulsars, whose parallax and proper motion have not been successfully fitted with timing observations or show obvious differences with corresponding latest VLBI solutions, and do further studies on their timing properties. After updating astrometric parameters in pulsar ephemerides with the latest VLBI measurements, we derive the latest rotation solutions of these pulsars with observation data at S and C$\textrm{-}$band obtained from the Shanghai Tian Ma Radio Telescope (TMRT). Compared with spin frequency $\nu$ inferred from previous rotation solutions, the newly$\textrm{-}$fitted $\nu$ show differences larger than 10$^{-9}$ Hz for most pulsars. The contribution of the Shklovsky effect to period derivative $\dot{P}$ can be properly removed taking advantages of accurate proper motion and distance of target pulsars measured by VLBI astrometry. This further leads to a precise estimate of intrinsic characteristic age $\tau_{\rm c}$. Differences between the newly$\textrm{-}$measured $\tau_{\rm c}$ and corresponding previous results are as large as 2% for some pulsars. VLBI astrometric parameter solutions also lead to better measurements of timing irregularities. For PSR B0154$+$61, the glitch epoch (MJD 58279.5) measured with previous ephemeris is about 13 d later than the result (MJD 58266.4) obtained with VLBI astrometric parameter solutions.

中文翻译：

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16颗脉冲星的新计时测量结果

脉冲星的位置、自行和视差是时序方程中的重要参数。通过脉冲星计时来准确拟合天体测量参数是一项非常具有挑战性的工作，尤其是对于显示出不规则计时特性的脉冲星。随着相关技术的快速发展，利用甚长基线干涉测量法（VLBI）以与模型无关的方式测量越来越多的脉冲星的天体测量参数成为可能。在这项工作中，我们选择了 16 颗视差和自行未成功拟合定时观测或与相应的最新 VLBI 解决方案存在明显差异的正常脉冲星，并对其定时特性进行了进一步研究。在使用最新的 VLBI 测量值更新脉冲星星历中的天体测量参数后，我们利用从上海天马射电望远镜 (TMRT) 获得的 S 和 C$\textrm{-}$ 波段观测数据推导出这些脉冲星的最新旋转解。与从先前旋转解推断的自旋频率 $\nu$ 相比，新的 $\textrm{-}$fitted $\nu$ 对大多数脉冲星显示出大于 10$^{-9}$Hz 的差异。Shklovsky效应对周期导数$\dot{P}$的贡献可以利用VLBI天体测量测量的目标脉冲星的精确自行和距离来适当去除。这进一步导致对内在特征年龄 $\tau_{\rm c}$ 的精确估计。对于某些脉冲星，新的 $\textrm{-}$measured $\tau_{\rm c}$ 与相应的先前结果之间的差异高达 2%。VLBI 天体测量参数解决方案还可以更好地测量定时不规则性。