Insights into searches for anisotropies in the nanohertz gravitational-wave background
Insights into searches for anisotropies in the nanohertz gravitational-wave background
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DOI：
10.1103/physrevd.103.042009
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发表时间：
2020-10
影响因子：
5
通讯作者：
Yacine Ali-Haïmoud;Tristan L. Smith;C. Mingarelli
中科院分区：
文献类型：
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作者：
Yacine Ali-Haïmoud;Tristan L. Smith;C. Mingarelli
在接下来的几年里，脉冲星定时阵列(PTA)将被定位为探测可能由一组鼓舞人心的超大质量黑洞双星产生的随机引力波背景(GWB)，并可能限制一些奇异的物理现象。到目前为止，大多数脉冲星计时数据的分析都集中在GWB的单极上，假设它是完全各向同性的。自然而然的下一步是寻找GWB的各向异性。在这篇文章中，我们使用最近开发的PTA Fisher矩阵来深入了解GWB各向异性的最佳搜索策略。具体地说，我们将我们的结果应用于EPTA数据，使用其脉冲星的真实噪声特征。我们预测了GWB的可检测性，该GWB的角度相关性被假设为预定映射的线性组合，例如球谐或粗像素。我们发现，GWB单极子总是与这些映射在统计上相关，这意味着当同时搜索各向异性时，对单极子的敏感度降低。然后，我们导出了PTA最敏感的GWB强度的角分布，并说明了如何使用这些“主映射”来近似重建GWB的角依赖关系。由于主映射既不是完全各向异性的，也不是与单极不相关的，我们还发展了一个频率判据来专门寻找GWB中的各向异性，而不需要任何关于它们的角分布的先验知识。最后，我们展示了如何用我们的Fisher形式主义来恢复现有的EPTA结果，并阐明了它们的意义。这里介绍的工具对于指导和优化对脉冲星计时数据的计算要求很高的分析是很有价值的。
Within the next several years pulsar timing arrays (PTAs) are positioned to detect the stochastic gravitational-wave background (GWB) likely produced by the collection of inspiralling super-massive black holes binaries, and potentially constrain some exotic physics. So far most of the pulsar timing data analysis has focused on the monopole of the GWB, assuming it is perfectly isotropic. The natural next step is to search for anisotropies in the GWB. In this paper, we use the recently developed PTA Fisher matrix to gain insights into optimal search strategies for GWB anisotropies. For concreteness, we apply our results to EPTA data, using realistic noise characteristics of its pulsars. We project the detectability of a GWB whose angular dependence is assumed to be a linear combination of predetermined maps, such as spherical harmonics or coarse pixels. We find that the GWB monopole is always statistically correlated with these maps, implying a loss of sensitivity to the monopole when searching simultaneously for anisotropies. We then derive the angular distributions of the GWB intensity to which a PTA is most sensitive, and illustrate how one may use these "principal maps" to approximately reconstruct the angular dependence of the GWB. Since the principal maps are neither perfectly anisotropic nor uncorrelated with the monopole, we also develop a frequentist criterion to specifically search for anisotropies in the GWB without any prior knowledge about their angular distribution. Lastly, we show how to recover existing EPTA results with our Fisher formalism, and clarify their meaning. The tools presented here will be valuable in guiding and optimizing the computationally demanding analyses of pulsar timing data.