Observations of the Sun with the 32 Element MWA Prototype

Details Observations of the Sun with the 32 Element MWA Prototype Observations of the Sun with the 32 Element MWA Prototype

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh23b1548r&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH23B-1548

Astronomy and Astrophysics

Astrophysics

[6924] Radio Science / Interferometry, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions, [7594] Solar Physics, Astrophysics, And Astronomy / Instruments And Techniques

Scientific paper

The Murchison Widefield Array (MWA), a radio interferometer designed to operate in the 80-300 MHz band, is currently under construction in the remote and radio quiet Western Australian outback (Oberoi et al., 2009). An engineering prototype comprised of 32 elements, referred to as the 32T system, has been constructed on site to serve as an end-to-end test-bed for integration and performance testing of the hardware, firmware and software components. The 32T provides an opportunity to field test the system and gain useful experience in diverse domains including field deployment of the system, field and remote operations, reliability of the system, robustness of the monitor and control framework and, assessment of data quality. It also provides valuable datasets with which to develop and tune the calibration and imaging system. In addition to serving the system engineering goals, the 32T system is also intended to provide an opportunity for some early science observations. the MWA design is extremely well suited for solar observations (Oberoi et al., 2009) and radio images are in the MWA band are an excellent probe of the electron density and temperature distributions in the lower corona (Benkevitch et al., 2009). Here we present some early observations of the Sun with the 32T system. The unexpectedly deep and long-lived solar minimum during which these observations were taken (Nov 18-19, 2008) makes them especially interesting. Though the collecting area of the 32T system is only ~6% of that for the full MWA, for imaging a bright source like the sun, this does not pose a big disadvantage. The comparatively uniform uv-coverage resulting from its randomized Reuleaux triangle configuration is well suited for solar observations and the maximum baselines of about 300 m provide sufficient resolution, especially at the higher frequencies. Currently, the 32T system can provide 1.28 MHz of bandwidth, which is shortly expected to increase to 30.72 MHz. The 32T system is therefore a sufficiently capable instrument to explore many different aspects of imaging the sun at low radio frequencies. We present the first calibrated brightness temperature synthesis images of the sun at 5 frequencies between 85 and 235 MHz. We compare our observations against expectations from the commonly accepted coronal models and the observed flux densities with those obtained from other sources. Our observations show reasonable agreement with models, provide a satisfactory validation of the data quality from the array, and demonstrate the usefulness of the 32T system as a scientific instrument. More observations are planned to continue to characterize the large-scale structure of the corona as the new solar cycle progresses.

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