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Astrophysics Research Centre

School of Mathematics and Physics


The space radiation environment at 680 km altitude explored with flare patrol images from the Hinode X-Ray Telescope

  • Submitted by: Masanori Yamada, Ibaraki University, Ibaraki University, ISAS/JAXA
  • Authors: M. Yamada, T. Shimizu, T. Sakao & S. Nozawa
  • Session: Monday morning posters.

Lots of speckle may be seen on images, when high energy particles impact on CCD detectors. Since significant numbers of speckles appears during the passage in the South Atlantic Anomaly (SAA), the Hinode X-Ray Telescope (XRT) does not acquire images in the SAA passage. Speckles may also be observed when Hinode is in the high latitude near the Earth’s poles. They may be originated in high energy particles (protons and electrons) trapped in the Earth’s magnetosphere. Furthermore, the number of speckles may be suddenly increased when solar energetic particle (SEP) events happen. Quantitatively counting the number of speckles on the XRT images as a function of the spacecraft position on orbit and as a function of time may provide useful information for exploring the space environment at the altitude of 680 km. The XRT takes flare patrol images (256x256 pixel, 4x4 summation, 8msec exposure, Ti-poly filter) in high cadence (every 30-60 sec in typical). The flare patrol images are downlinked to the ground and available for counting the number of speckles.

At high latitude in the northern and southern hemispheres, slight increase on the number of speckle is observed like a belt, probably caused by high-energy electrons in radiation belt. When the SEP events occur, increase on the number of speckle is observed in the region between the high latitude belt and the pole. The most significant example is 7th March 2012 event, in which the number of speckles was much increased to 100 counts/cm2/s there. Another example was the SEP event on 23rd January 2012, in which the number of speckle was increased to 10 counts/cm2/s there, which is one order of magnitude smaller than that of the 7th March 2012 event. It should be noted that the flux of >10 MeV protons measured by GOES at 36,000 km altitude is approximately same in these two events. The difference in the proton flux can be well seen in >100 MeV measurements; ~100 counts/cm2/s/sr in the 7th March 2012 event vs. a few counts/cm2/s/sr in the 23rd January 2012 event. The comparison of the measurements suggests that high-energy proton flux in > several tens of MeV may control the number of speckles seen on the XRT images, i.e., the flux of protons coming down to the 680 km altitude at the polar regions during the SEP events.

public/hinode9/schedule/session-01p/v0040.txt · Last modified: 2015/07/30 00:37 (external edit)


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