1 Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
2 International Centre for Radio Astronomy Research, The University of Western Australia, Crawley, WA 6009, Australia. Electronic address: andreas.wicenec@icrar.org.
3 Key Laboratory of Radio Astronomy, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China. Electronic address: antao@shao.ac.cn.