Testing the Binary Hypothesis: Pulsar Timing Constraints on Supermassive Black Hole Binary Candidates
Testing the Binary Hypothesis: Pulsar Timing Constraints on Supermassive Black Hole Binary Candidates
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DOI：
10.3847/1538-4357/aaad0f
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发表时间：
2017-03
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影响因子：
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通讯作者：
A. Sesana;Z. Haiman;B. Kocsis;L. Kelley
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作者：
A. Sesana;Z. Haiman;B. Kocsis;L. Kelley
时域天文学的出现正在彻底改变我们对宇宙的理解。诸如“卡塔利纳实时瞬变测量”（CRTS）或“帕洛玛瞬变工厂”（PTF）等项目对数百万个物体进行了数年的调查，从而可以对大型统计样本进行变异性研究。在CRTS中对250 k类星体的检查产生了111个潜在周期源的目录，提出了超大质量黑洞双星（SMBHB）候选者。对PTF数据进行的类似调查从一个35K类星体样本中产生了33个候选者。在SMBHB假设下工作，我们计算隐含的SMBHB合并率，并使用它来构建预期的引力波背景（GWB）在纳赫兹频率，探测脉冲星定时阵列（PTA）。校正后的不完整性，并假设维里质量估计，我们发现，GWB暗示的CRTS样品超过目前最严格的PTA上限几乎一个数量级。在进一步校正维里质量测量中的隐式偏差后，隐式GWB显著下降，但仍与最严格的PTA上限保持紧张关系。PTF样品的结果相似。贝叶斯模型选择表明，CRTS和PTF样本的零假设（候选样本为假阳性）优于二元假设，分别约为2.3σ和3.6σ。虽然不是决定性的，但我们的分析强调了PTA作为单个SMBHB候选者的天体物理探针的潜力，并表明CRTS和PTF样品可能受到几个假阳性的污染。
The advent of time domain astronomy is revolutionizing our understanding of the universe. Programs such as the Catalina Real-time Transient Survey (CRTS) or the Palomar Transient Factory (PTF) surveyed millions of objects for several years, allowing variability studies on large statistical samples. The inspection of ≈250 k quasars in CRTS resulted in a catalog of 111 potentially periodic sources, put forward as supermassive black hole binary (SMBHB) candidates. A similar investigation on PTF data yielded 33 candidates from a sample of ≈35 k quasars. Working under the SMBHB hypothesis, we compute the implied SMBHB merger rate and we use it to construct the expected gravitational wave background (GWB) at nano-Hz frequencies, probed by pulsar timing arrays (PTAs). After correcting for incompleteness and assuming virial mass estimates, we find that the GWB implied by the CRTS sample exceeds the current most stringent PTA upper limits by almost an order of magnitude. After further correcting for the implicit bias in virial mass measurements, the implied GWB drops significantly but is still in tension with the most stringent PTA upper limits. Similar results hold for the PTF sample. Bayesian model selection shows that the null hypothesis (whereby the candidates are false positives) is preferred over the binary hypothesis at about 2.3σ and 3.6σ for the CRTS and PTF samples respectively. Although not decisive, our analysis highlights the potential of PTAs as astrophysical probes of individual SMBHB candidates and indicates that the CRTS and PTF samples are likely contaminated by several false positives.