MIRANdA: A First Step to the Square Kilometre Array

by Russ Taylor

The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 100 times more sensitive than any existing radio facility.  The SKA will be built in a staged program, beginning with Pathfinders at the 1% scale, on the 2008 – 2012 time frame, evolving to construction of SKA Phase I around 2015 (10% of the collecting area of the SKA) which will be expanded over time to the full SKA by around 2020. The Pathfinders are being designed to prototype and demonstrate at a significant scale the new science enable by the SKA and technologies that will enable it.

The SKA will impact a wide range of science from fundamental physics to cosmology and astrobiology. Compelling questions that will be addressed as key science investigations include:

· understanding the cradle of life by imaging the environments of the formation of earth-like planets, the precursors to biological molecules, and carrying out an ultra-sensitive search for  evidence of  extra-terrestrial intelligence,

• carrying out fundamental tests of the theory of gravity by using radio waves to measure the strong space-time  warp of pulsars and black holes and timing of arrays of pulsars over large areas of the sky to detect long-wavelength gravity waves propagating through the Galaxy,
• tracing the origin and evolution of cosmic magnetism by measuring the properties of polarized radio waves from galaxies over cosmic history
• charting the cosmic evolution of galaxies and large-scale structure, the cosmological properties of the universe and dark energy the imaging of atomic hydrogen emission from galaxies and the cosmic web from the present to time of the first galaxies, and
• probing the dark ages and the epoch of reionization of the Universe when the first compact sources of energy emerged.

In November 2006 the President of National Research Council of Canada and the Chief Executive Officer of the Australian Commonwealth Science and Industrial Research Organization signed an understanding declaring their intention to collaborate in the construction of MIRANdA; an SKA Pathfinder constructed on the site in Western Australia that is the proposed Australian site for the SKA – one of the most radio quiet regions on Earth.  MIRANdA, which is expected to grow into SKA Phase I, will be based on the Reference Design of the SKA, a large number of small parabolic dishes equipped with new feed and receiver technology to expand the instantaneous field-of-view. 

Figure 1. The Site in Western Australia for the MIRANdA SKA Pathfinder is one of the most radio-quiet locations on the Earth, allowing radio observations outside of the protected frequency bands.

The Science

A majority of the key science for the SKA can be addressed at the mid-frequency range of the SKA from 300 MHz to a few GHz.  The Phase I SKA targets this frequency range for the initial operation.  MIRANdA is aimed squarely at this frequency range, coupled with the development and deployment of phase-array feed systems.  This combination will produce a powerful synoptic survey instrument that will make substantial advance on three of the SKA key science projects; the origin and evolution of cosmic magnetism, the evolution of galaxies and large scale structure, and strong field tests of gravity.  A low-frequency array prototype of the all-sky monitor component of the SKA reference design is being built at the same site, and will target the epoch of reionization and the dark ages.

Headline goals for MIRANdA are:

• The detection of a million galaxies in atomic hydrogen emission across 80% of the sky out to a redshift of 0.2 to understand galaxy formation and gas evolution in the nearby Universe.
• The detection of synchrotron radiation from 60 million galaxies to determine the evolution, formation and population of galaxies across cosmic time and enabling key cosmological tests.
• The detection of polarized radiation from over 500,000 galaxies, allowing a grid of rotation measures at 10' spacing across the sky to understand how the Milky Way generates and maintains coherent magnetic fields on huge scales, and allowing our first steps in the exploration of the evolution of magnetic fields in galaxies over cosmic time.
• The understanding of the evolution of the interstellar medium of our own Galaxy and the processes that drive the chemical and physical evolution of matter through observations of interstellar matter in atomic, molecular, ionized and magnetized forms.
• The characterization of the radio transient sky through detection and monitoring of transient sources such as gamma ray bursts, radio supernovae and intra-day variables.
• The discovery and timing of  a thousand new radio pulsars.
• The high-resolution imaging of intense, energetic phenomena by enlarging the Australian and global Very Long Baseline Array networks.

These scientific programs constitute a significant initial step toward the SKA science goals.  This science in enabled by the unique radio quiet location in Western Australia and the innovation that prototype the key SKA reference design technologies. MIRANdA will be a world-leading radio astronomy facility that will uniquely pathfind the scientific and technical direction to the SKA.

The Telescope

MIRANdA will be located at Boolardy Station in Western Australia, approximately 1000 km northeast of Perth.  The collecting area of MIRANdA is initially a few percent of that of the SKA and is designed with an upgrade path to SKA Phase I and to the full SKA.

Figure 2. Focal-plane phase-array feeds coupled with 12-m diameter parabolic reflectors will give MIRANdA an unprecedented instantaneous field of view.

MIRANdA will initially consist of a central core of 45 12-m diameter dishes spread over an area of about 10 km in size. A remote station, a few thousand kilometres away in NSW, will be used to prototype the long-baseline functionality of the SKA.  Focal plane phased-array technology, under development in Canada and Australia, will produce 30 simultaneous beams on the sky, providing a field-of-view of 30 square degrees.  The initial frequency range will be 0.8 to 1.7 GHz, with instantaneous bandwidth 0.3 GHz and 16,000 spectral channels.

The large field-of-view makes MIRANdA an unprecedented synoptic radio telescope. The area of the field-of view is over 100 times larger than that of the Very Large Array.  Images of very large areas of the sky to sensitivities currently only achievable in very small regions will be routine.  New ways of observing the Universe in radio waves will become possible that allow us detect radiation instantaneously from large volumes of the Universe and mine the scientific information it contains about the physics, original, evolution and fate of the Universe.

The Canadian SKA Science Advisory Committee

www.ska.ca