Fast single-dish scans of the Sun using ALMA

Kavli Affiliate: Richard Hills

| First 5 Authors: Neil Phillips, Richard Hills, Tim Bastian, Hugh Hudson, Ralph Marson

| Summary:

We have implemented control and data-taking software that makes it possible
to scan the beams of individual ALMA antennas to perform quite complex patterns
while recording the signals at high rates. We conducted test observations of
the Sun in September and December, 2014. The data returned have excellent
quality; in particular they allow us to characterize the noise and signal
fluctuations present in this kind of observation. The fast-scan experiments
included both Lissajous patterns covering rectangular areas, and double-circle
patterns of the whole disk of the Sun and smaller repeated maps of specific
disk-shaped targets. With the latter we find that we can achieve roughly
Nyquist sampling of the Band~6 (230~GHz) beam in 60~s over a region 300$"$ in
diameter. These maps show a peak-to-peak brightness-temperature range of up to
1000~K, while the time-series variability at any given point appears to be of
order 0.5 percent RMS over times of a few minutes. We thus expect to be able to
separate the noise contributions due to transparency fluctuations from
variations in the Sun itself. Such timeseries have many advantages, in spite of
the non-interferometric observations. In particular such data should make it
possible to observe microflares in active regions and nanoflares in any part of
the solar disk and low corona.

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