AI 中文总结
研究日球层密度变化对脉冲星计时阵列探测引力波的影响，核心方法是用IPS-UCSD模型处理MeerKAT PTA数据集，主要贡献是发现时变球对称模型在特定条件下可减轻日球层时间延迟影响，并提议用精确脉冲星改进密度模型。
AI 中文摘要
日球层密度变化会给毫秒脉冲星的脉冲到达时间带来延迟。对这些变化建模不当可能影响脉冲星计时阵列（PTA）对引力波的探测和特征描述。目前PTA通常采用时变球对称日球层模型，无法捕捉日球层完整的时空复杂性。本文研究基于行星际闪烁（IPS）测量的日球层三维时间相关模型——IPS-UCSD模型能否用于减轻PTA分析中的太阳风影响。将该模型应用于MeerKAT PTA 4.5年数据集，评估其能否校正日球层密度变化及对引力波灵敏度的影响。结果发现该模型不能准确校正日球层引起的计时畸变，导致恢复的引力波参数出现偏差。通过模拟表明球对称日球层模型也无法完全捕捉IPS-UCSD模型中的密度变化。然而，如果对星际色散量（DM）变化也进行建模，日球层模型误差会被DM变化部分吸收，减少引力波信号污染。因此发现在典型PTA射频下，时变球对称模型足以减轻日球层时间延迟对恢复的引力波结果的影响，前提是对其他信号成分也进行建模。还提议未来可利用计时最精确的脉冲星改进数据驱动的日球层密度模型。
英文摘要
Heliospheric density variations impart delays on pulse times of arrivals from millisecond pulsars. Improper modelling of these variations may affect gravitational wave detection and characterisation by pulsar timing arrays (PTAs). Currently, PTAs typically employ a time-varying, spherically symmetric heliosphere model, which does not capture the full spatial and temporal complexity of the heliosphere. Instead, we investigate whether a three-dimensional, time-dependent model of the inner heliosphere from interplanetary scintillation (IPS) measurements - the IPS-UCSD model - can be employed to mitigate the solar wind in PTA analyses. We applied the IPS-UCSD model to the MeerKAT PTA 4.5-year dataset to assess whether it could correct for heliospheric density variations, and the impact on GW sensitivity compared to a spherically-symmetric model. We find that the model does not accurately correct for heliosphere-induced timing distortions, leading to bias in recovered GW parameters. Using simulations, we show that the spherically symmetric heliosphere model also fails to fully capture heliospheric density variations like those in the IPS-UCSD model. However, if interstellar dispersion measure (DM) variations are also modelled, then the heliospheric model errors are partially absorbed by DM variations, reducing contamination of the GW signal. Therefore we find that a time-varying spherically symmetric model is sufficient to mitigate the effect of heliospheric time delays on recovered GW results at typical PTA radio frequencies, provided other signal components are also modelled. We propose that the most precisely timed pulsars may be used to improve data-driven heliospheric density models in the future.
Comments14 pages, 9 figures
