Noise characterization for pulsar-timing applications accounts for interstellar dispersion by assuming a known frequency dependence of the delay it introduces in the times of arrival (TOAs). However, calculations of this delay suffer from misestimations due to other chromatic effects in the observations. The precision in modeling dispersion is dependent on the observed bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs due to misestimations in the modeling of dispersion when using varying bandwidths at the Green Bank Telescope. We use a set of broadband observations of PSR J1643−1224, a pulsar with unusual chromatic timing behavior. We artificially restricted these observations to a narrowband frequency range, then used both the broad- and narrowband data sets to calculate residuals with a timing model that does not account for time variations in the dispersion. By fitting the resulting residuals to a dispersion model and comparing the fits, we quantify the error introduced in the timing parameters due to using a reduced frequency range. Moreover, by calculating the autocovariance function of the parameters, we obtained a characteristic timescale over which the dispersion misestimates are correlated. For PSR J1643−1224, which has one of the highest dispersion measures (DM) in the NANOGrav pulsar timing array, we find that the infinite-frequency TOAs suffer from a systematic offset of ∼22 μs due to incomplete frequency sampling, with correlations over about one month. For lower-DM pulsars, the offset is ∼7 μs. This error quantification can be used to provide more robust noise modeling in the NANOGrav data, thereby increasing the sensitivity and improving the parameter estimation in gravitational wave searches.

中文翻译：

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NANOGrav 12.5 年数据集：不同带宽的色散测量误估计

脉冲星定时应用的噪声表征通过假设其在到达时间 (TOA) 中引入的延迟的已知频率依赖性来解释星际色散。然而，由于观测中的其他色度效应，这种延迟的计算会出现错误估计。色散建模的精度取决于观测到的带宽。在这项工作中，我们计算了在绿岸望远镜使用不同带宽时由于色散建模中的错误估计而导致的无限频率 TOA 的偏移。我们使用 PSR J1643−1224 的一组宽带观测，这是一颗具有不寻常的色度定时行为的脉冲星。我们人为地将这些观测结果限制在窄带频率范围内，然后使用宽带和窄带数据集通过不考虑色散时间变化的时序模型来计算残差。通过将所得残差拟合到色散模型并比较拟合结果，我们量化了由于使用缩小的频率范围而在时序参数中引入的误差。此外，通过计算参数的自协方差函数，我们获得了离散误估计相关的特征时间尺度。对于 PSR J1643−1224，它在 NANOGrav 脉冲星定时阵列中具有最高的色散测量 (DM) 之一，我们发现无限频率 TOA 的系统偏移为 ∼22μ由于频率采样不完整，相关性超过一个月。对于低DM脉冲星，偏移量为∼7μs。这种误差量化可用于在 NANOGrav 数据中提供更稳健的噪声建模，从而提高灵敏度并改进引力波搜索中的参数估计。