NICER / ISS Science Nugget for August 9, 2018

Space weather study guides background estimates for NICER data

NICER's key science is very sensitive to the instrumental background level. NICER avoids collecting prime science data during passages through the South Atlantic Anomaly (SAA) which always has enhanced background. When the ISS is over the "Polar Horn" regions at the most northern and southern latitudes, the background is also high, but variable with space weather.

This past summer, NICER interns examined using various space weather indices to filter archived data to select out the highest quality low background data. They found that the Geomagnetic Activity ("Kp") index provided by NOAA has an excellent correlation with Polar Horn background (see figure). Furthermore, NOAA predictions of "Kp" can be used to optimize NICER science planning 3 days ahead. This data is also being used to build a background spectral model that can be applied for all NICER observations.

Figure: The NICER X-ray background spectra (Counts/second vs Channel in units of 10 eV) collected in the Polar Horn Regions at various Space Weather "Kp" index values.

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