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arXiv 1101.3759gr-qcastro-ph.IM
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脉冲星对甚低频引力波的计时灵敏度

Pulsar Timing Sensitivity to Very-Low-Frequency Gravitational Waves

Fredrick A. Jenet, J. W. Armstrong, Massimo Tinto

摘要:

在纳赫兹频率下,引力波(GW)会引起脉冲星信号到达时间的变化,而脉冲星信号的到达时间可以通过精确的定时观测来测量。在这里,我们计算甚低频GW的灵敏度约束的仪器,传播和其他噪音从根本上限制脉冲星定时观测。达到预期的GW信号强度将需要估计和消除由典型的星际等离子体湍流引起的到达时间波动的$\simeq$ 99%,并将白均方根定时噪声减少到$\sim$ 100纳秒或更少。单脉冲星信噪比(SNR)= 1的灵敏度则受到$h_{rms} \sim$ 2 $\times 10^{-16}$的最佳现行地面时间标准的限制[f/(1周期/年)] $^{-1/2}$,用于$f < 3 \times 10^{-8}$ Hz,其中f是傅立叶频率,假设带宽为1周期/(10年)。这个灵敏度包络可能是乐观的,因为它假设可以忽略不计的内在脉冲星旋转噪声,从时间标准到天文台的完美时间传递,以及稳定的脉冲轮廓。尽管如此,它可以与预测的信号水平的宽带天体物理GW背景的超大质量黑洞二进制。这种背景仅在低于约1周/(10年)的频率下可与计时噪声相比,这表明可靠的探测将需要通过脉冲星阵列信号处理大大提高信噪比。

英文摘要:

At nanohertz frequencies gravitational waves (GWs) cause variations in time-of-arrival of pulsar signals potentially measurable via precision timing observations. Here we compute very-low-frequency GW sensitivity constrained by instrumental, propagation, and other noises fundamentally limiting pulsar timing observations. Reaching expected GW signal strengths will require estimation and removal of $\simeq$99% of time-of-arrival fluctuations caused by typical interstellar plasma turbulence and a reduction of white rms timing noise to $\sim$100 nsec or less. If these were achieved, single-pulsar signal-to-noise ratio (SNR) = 1 sensitivity is then limited by the best current terrestrial time standards at $h_{rms} \sim$2 $\times 10^{-16}$ [f/(1 cycle/year)]$^{-1/2}$ for $f < 3 \times 10^{-8}$ Hz, where f is Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. This sensitivity envelope may be optimistic in that it assumes negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles. Nonetheless it can be compared to predicted signal levels for a broadband astrophysical GW background from supermassive black hole binaries. Such a background is comparable to timekeeping-noise only for frequencies lower than about 1 cycle/(10 years), indicating that reliable detections will require substantial improvements in signal-to-noise ratio through pulsar array signal processing.

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