Metrewave observations of the Sun

D. Oberoi1*, R. Sharma1, S. Bhatnagar2, C. J. Lonsdale3, L. D. Matthews3, I. H. Cairns4, S. J. Tingay5, L. Benkevitch3, A. Donea6, S. M. White7, G. Bernardi8, J. D. Bowman9, F. Briggs10, R. J. Cappallo3, B. E. Corey3, A. Deshpande11, D. Emrich5, B. M. Gaensler4,12, R. Goeke13, L. J. Greenhill14, B. J. Hazelton15, M. Johnston-Hollitt16, D. L. Kaplan17, J. C. Kasper18, E. Kratzenberg3, M. J. Lynch5, S. R. McWhirter3, D. A. Mitchell19,12, M. F. Morales15, E. Morgan13, S. M. Ord5, T. Prabu11, A. E. E. Rogers3, A. Roshi20, J. E. Salah3, N. Udaya-Shankar11, K. S. Srivani11, R. Subrahmanyan11,12, M. Waterson5, R. B. Wayth5, R. L. Webster21,12, A. R. Whitney3, A. Williams5 and C. L. Williams13
1National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India
2National Radio Astronomy Observatory, Socorro, NM, USA
3MIT Haystack Observatory, Westford, MA, USA
4University of Sydney, Sydney, Australia
5Curtin University, Perth, Australia
6Monash University, Melbourne, Australia
7Air Force Research Laboratory, Kirtland, NM, USA
8Square Kilometre Array South Africa (SKA SA), Cape Town, South Africa
9Arizona State University, Tempe, AZ, USA
10The Australian National University, Canberra, Australia
11Raman Research Institute, Bangalore, India
12ARC Centre for Excellence for All-sky Astrophysics (CAASTRO)
13MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA
14Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
15University of Washington, Seattle, WA, USA
16Victoria University of Wellington, New Zealand
17University of Wisconsin–Milwaukee, Milwaukee, WI, USA
18University of Michigan, Michigan, Ann Arbor, MI, USA
19CSIRO Computational Informatics, Marsfield, Australia
20National Radio Astronomy Observatory, Charlottesville, WV, USA
21The University of Melbourne, Melbourne, Australia

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High fidelity solar imaging at low radio frequencies remains a challenge. Solar emission is characterized by its large angular size, complex and dynamic morphological features spanning a large range of angular sizes, emission mechanisms spanning a wide range in brightness temperatures, and temporal and spectral variability of the emission over large ranges in time and frequency. Capturing the solar emission processes with high fidelity and in sufficient detail hence requires a capability to simultaneously track the emission in time, frequency and morphology over a large bandwidth. Traditional interferometers rely on time and frequency synthesis to produce high fidelity and dynamic range imaging, and are hence intrinsically poorly suited to the task of instantaneous imaging over narrow spectral spans.

With the emergence of a new generation of large-N interferometers, the situation has improved in a very significant manner. Of these instruments, the Murchison Widefield Array (MWA), located at the site chosen for the SKA in Western Australia, is the one most suited for solar observations at low radio frequencies. The MWA has recently commenced routine observing. Here we illustrate the diversity of features seen in solar emission using the MWA data to substantiate its suitability for solar studies.

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Keywords : Sun: corona; Sun: activity; instrumentation: intereferometers