This award will be used to apply the design of low frequency radio astronomy technologies, developed at MIT under a previous NSF grant, to the construction of the Mileura Widefield Array-Low Frequency Demonstrator (MWA-LFD). The MWA-LFD is a collaboration of the Massachusetts Institute of Technology (MIT), Harvard-Smithsonian Center for Astrophysics (CfA), the Australian University Consortium, the Australian Telescope National Facility (ATNF), and the Western Australia government. The MWA-LFD will be located at the Mileura radio quiet site in the Western Australian desert. This scientifically capable array, consisting of 500 phased-array antennas feeding sophisticated digital signal processing systems, will have high sensitivity, broad 80-300 MHz frequency coverage, very high spectral and temporal resolution, electronic pointing agility and multi-beaming capability. Most importantly, it will feature an inherently very wide ~30 degrees instantaneous field of view. This combination of properties allows the demonstration array to perform cutting-edge science experiments with much better sensitivity than any existing instrument. This science capability will be available two years after the start of funding, and the last two years of the program will focus on science investigations with the array.
The science goals of the MWA-LFD are in three main areas of investigation. The highest priority is to detect and characterize redshifted neutral atomic hydrogen (HI) signals from the cosmological Epoch of Reionization. The array will be capable of measuring the power spectrum of fluctuations, as well as imaging structures created by Stromgren spheres around quasars at redshifts with z~6.5, providing the first view of the cosmic dark ages. and early structure formation in the Universe. Second, the wide field capabilities of the array will be exploited to perform a blind search for transient sources of radio emission which is 6 orders of magnitude more sensitive than any previous work in this frequency range. Third, the array will be used to probe the heliosphere with unprecedented precision using interplanetary scintillation (IPS) and Faraday rotation techniques. The Faraday rotation holds the unique promise of constraining the orientation of the magnetic field in coronal mass ejection (CME) events, which is essential for predicting the impact of solar storms on the earth. Several other scientific topics, such as pulsar studies, solar bursts, the local structure of the interstellar medium, and radio recombination lines, can also be effectively addressed with the array.
The MWA-LFD will demonstrate a broad range of technologies and techniques that are essential for the future feasibility and performance of full-scale wide field arrays that are currently in a conceptual stage of development. The MWA-LFD is relevant to cyber-infrastructure and cyber-science initiatives in the development of an astronomical telescope with no moving parts, all "actions" are handled electronically, and in the demonstration of new data handling techniques, involving massive, near real-time processing and preliminary analysis, followed by data compression. The application of the MWA-LFD to heliospheric measurements will make an important contribution to the National Space Weather Program, and thus will have valuable societal benefits. The project will be executed by multiple national and international partners, which offer opportunities for student exchange, and promotion of international scientific relations. The grant will train postdoctoral researchers and graduate students, and will engage undergraduate students and teachers in the project at no cost to the grant, through existing Research Experiences for Undergraduates (REU) and Research Experiences for Teachers (RET) programs at MIT and the Harvard-Smithsonian Center for Astrophysics (CfA). There will be extensive outreach activities to local area schools and communities.
The purpose of the Mileura Widefield Array (MWA) project was to develop and build a revolutionary new kind of telescope, operating at low radio frequencies (like those used for FM radio and TV broadcasting), to conduct a variety of astronomical and space weather investigations. The instrument site is in outback western Australia, well away from population centers and the radio interference they generate. The science goals include study of a very early stage in the evolution of the universe, known as the "epoch of reionization", when the first stars and galaxies were forming. The telescope was also designed to be very sensitive to time-variable radio emission from astronomical objects, and to see many more of these types of objects than before by exploiting its ability to make high-resolution images of an extraordinarily wide field of view of the sky, updated every few seconds. This field-of-view characteristic and rapid imaging capability also make the telescope very powerful as a means of surveying the sky quickly and with excellent sensitivity, enabling groundbreaking research on objects and phenomena both within our galaxy and beyond. Finally, the telescope was designed to probe the origin and behavior of violent disturbances in the solar wind that give rise to "space weather" events. These solar-generated storms in the near-earth environment are responsible for the auroras, as well as a wide range of impacts on human activities in space and on the ground. The telescope is constructed as thousands of small, simple antennas, tied together electronically. By spreading the antennas across a large area, about 3km across, it is possible to create a high-resolution "radio camera" through a technique known as interferometry. This requires that the incoming radio signals be converted to digital form, and that the resulting streams of numbers be manipulated at very high speed using complex algorithms. The data flows are massive, amounting to hundreds of gigabits per second, and the computing requirements are formidable. For this reason, telescopes of this architecture have not been possible until very recently. The MWA is largely a software telescope, and has no moving parts. The traditional telescope function of steering and pointing is done electronically, which allows the instrument to be very agile, and to move its focus around the sky in fractions of a second. The architecture also is optimized to provide the largest possible field of view in a single observation − typically 1000 square degrees at a time, which is scientifically very powerful. Most of the effort funded by this award was in the detailed technical design of the telescope. The project was a large international partnership, with major contributions from the US, Australia and India. The US team was responsible for the design of the antennas and the radio signal path up to the point of being digitized. The combination of the signals into a data stream that could be used as a "radio camera", namely the formation of interferometer products, was a US task. The US team also developed the complex algorithms and software systems, known as the "real time system" or RTS, required to compensate for distortions of the signals from a wide variety of causes. The overall design of the telescope was spearheaded by the US team, and contributions to the detailed design were made throughout the system. Extensive data analysis from prototype systems was performed, and development of calibration and analysis techniques for the specific science goals, most notably the early universe studies, was done. A number of early science results were obtained and reported in conferences and journals. Due to a diverse set of issues, both external and internal to the project, construction of the telescope was not completed before the end of the award period. However, the Australian and Indian partners have provided funds to complete the system. The final telescope will have considerably fewer antennas than originally planned with a corresponding loss of sensitivity, but with significantly more flexibility in operation, and a longer expected lifetime. As of March 2012 construction activity at the telescope site is in full swing, and physical completion of the instrument is expected by the end of 2012. US researchers remain partners in the project, with full rights to the data. Future use of the telescope for astronomical and space-weather research will be supported by new NSF awards, or other sources. The technologies, algorithms and techniques developed during the project are directly applicable to other radio arrays, both existing and planned, and many of these are already in the open literature.
