The detection of a neutron star merger by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo gravitational wave detectors and the subsequent detection of an electromagnetic counterpart has opened a new era of transient astronomy. With upgrades to the Advanced LIGO and Advanced Virgo detectors and new detectors coming online in Japan and India, neutron star mergers will be detected at a higher rate in the future, starting with the O3 observing run which will begin in early 2019. The detection of electromagnetic emission from these mergers provides vital information about merger parameters and allows independent measurement of the Hubble constant. The Australian Square Kilometre Array Pathfinder (ASKAP) is expected to become fully operational early 2019 and its 30 deg$^2$ field of view will enable us to rapidly survey large areas of sky. In this work we explore prospects for detecting both prompt and long-term radio emission from neutron star mergers with ASKAP and determine an observing strategy that optimises the use of telescope time. We investigate different strategies to tile the sky with telescope pointings in order to detect radio counterparts with limited observing time, using 475 simulated gravitational wave events. Our results show a significant improvement in observing efficiency when compared with a naïve strategy of covering the entire localisation above some confidence threshold, even when achieving the same total probability covered.
Solar, Heliospheric and Ionospheric Physics: Pathfinders, Precursors and SKAO Perspective
ASTRON - Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；Indian Institute of Technology, Kanpur（坎普尔印度理工学院）；National Centre for Radio Astrophysics, Tata Institute of Fundamental Research（塔塔基础研究院国家射电天体物理中心）；Dublin Institute for Advanced Studies（都柏林高等研究院）；University of Oslo（奥斯陆大学）；University of Bath（巴斯大学）
A method for efficient measurement of gravitational lens time delays
哈勃常数值目前已知的准确度为10%，除非对宇宙学进行假设（Sandage et al. 2006）。引力透镜系统提供了另一种使用时间延迟测量的哈勃常数探测器。然而，目前的调查约20个时间延迟透镜，虽然不同程度的复杂性，导致不同的值的哈勃常数范围从50-80公里/秒/百万秒差距。为了减少不确定性，更多的时间延迟测量与更好地确定质量模型是必不可少的（Oguri 2007，Saha等人2006）。我们提出了一种更有效的技术测量时间延迟，不需要定期监测与高分辨率的干涉仪阵列。该方法使用双像和长轴四透镜系统，其中较亮的分量首先变化并主导总通量密度。用低分辨率但高灵敏度的射电望远镜监测总通量密度提供了较亮图像的变化，并用于触发高分辨率观测，然后可以用来看到较暗图像的变化。我们提出了这种方法的模拟与试点项目一起使用WSRT（韦斯特博克射电综合望远镜）触发VLA（甚大阵）的意见。这种新方法很有希望测量时间延迟，因为它在高分辨率望远镜上使用相对较少的时间。这将是重要的，因为许多SKA探路者望远镜，如MeerKAT（卡鲁阵列望远镜）和ASKAP（澳大利亚平方公里阵列探路者），具有高灵敏度，但分辨率有限。
