Main Objective: Full-Sun multi-filter observation by XRT
Scientific Justification: This campaign requests to allocate a few hours of disk center pointing hopefully every day outside the period of other HOPs and core observations (e.g., AR tracking). The main purpose of this campaign is to increase the number of XRT's synoptic type images(fullsun images by multi-filters) per day. XRT synoptic images are used to derive soft X-ray solar irradiance by combining the filter-ratio analysis of the disk-integrated XRT signals with the calculation of energy flux (W/m^2) emitted from the model coronal plasma in a given wavelength range (e.g., 1-8A).
The soft X-ray irradiance obtained with Yohkoh/SXT (1991-2001) in the same method had an excellent correlation with the GOES/XRS 1-8A flux except the period around the solar minimum. Around the solar minimum, the solar flux went close or under the detection limit of GOES/XRS, but Yohkoh/SXT consistently yielded the irradiance values under 10^(-8)W/m^2. This shows the advantage of the filter-ratio irradiance over the GOES/XRS when the solar activity is approaching to the minimum (as of this writing, no information is yet delivered regarding the performance of the new XRS instrument on-board GOES-16 launched in late 2016). To perform the irradiance study with XRT filter-ratios, it is highly preferable to increase the number of data set to improve the time resolution. Another purpose of this campaign is to watch the full-disk corona for catching eruptive events from unexpected places. While the ARs as a source of flares and CMEs are decreasing in both numbers and sizes in coming few years, eruptive events can also occur from quieter regions (e.g., a part of filament or old plage region). Since such events are often associated with the heated plasma that is efficiently detected in soft X-ray, full-disk image sequences obtained with XRT will provide unique data set to study eruptive events over other full-disk instruments using the light from cooler plasma.
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