论文标题
低频极化无线电干涉仪的灵敏度
Sensitivity of a Low-Frequency Polarimetric Radio Interferometer
论文作者
论文摘要
目的:本文旨在得出极化无线电干涉仪的灵敏度的表达,该干涉仪可用于全天空观察任意极化源,而对FOV的限制也不具有有关源源极化状态的任何先验假设。我们使用Murchison Wideffield阵列(MWA)望远镜验证了所得公式。方法:灵敏度表达是通过将系统等效通量密度(SEFD)的概念应用于极化无线电干涉仪而不是通过计算$ a_e/t_ {sys} $来开发的。 SEFD是根据由于系统噪声引起的目标源的噪声通量密度估计的标准偏差计算得出的。结果:偏振无线电干涉仪的SEFD通常不是单极化干涉仪的$ 1/\ sqrt {2} $,正如通常假定的狭窄FOV一样。此假设可能会导致基于双偏振偶极子的系统的重大错误,该系统在低频射电天文学中很常见:最多$ \ sim 15 \%15 \%$,对于$ 45^\ circ $ $ $ \ $ \ sim45 \%$ $ 60^\ circ $ copdage $ 45^\ circ $ $ 45^\ circ $。最坏的情况发生在偶极子的对角线中,以进行非常宽的FOV。这是通过理论,模拟和观察结果证明的。此外,使用所得的配方,对非重组灵敏度的计算是直接且明确的。结论:对于与低频无线电干涉仪有关的广泛的FOV观测值,例如SKA-LOW,狭窄的FOV和单极敏感性表达式不正确,应由本文中得出的公式代替。
Aims: This paper aims to derive an expression for the sensitivity of a polarimetric radio interferometer that is valid for all-sky observations of arbitrarily polarized sources, with neither a restriction on FoV nor with any a priori assumption regarding the polarization state of the source. We verify the resulting formula with an all-sky observation using the Murchison Widefield Array (MWA) telescope. Methods: The sensitivity expression is developed from first principles by applying the concept of System Equivalent Flux Density (SEFD) to a polarimetric radio interferometer not by computing $A_e/T_{sys}$. The SEFD is calculated from the standard deviation of the noisy flux density estimate for a target source due to system noise. Results: The SEFD for a polarimetric radio interferometer is generally not $1/\sqrt{2}$ of a single-polarized interferometer as is often assumed for narrow FoV. This assumption can lead to significant errors for a dual-polarized dipole based system, which is common in low-frequency radio astronomy: up to $\sim 15\%$ for a zenith angle (ZA) coverage of $45^\circ$, and up to $\sim45\%$ for $60^\circ$ coverage. The worst case errors occur in the diagonal planes of the dipole for very wide FoV. This is demonstrated through theory, simulation and observations. Furthermore, using the resulting formulation, calculation of the off-zenith sensitivity is straightforward and unambiguous. Conclusions: For wide FoV observations pertinent to low-frequency radio interferometer such as the SKA-Low, the narrow FoV and the single-polarized sensitivity expressions are not correct and should be replaced by the formula derived in this paper.