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Proton Hits and Hot Pixels

7 Apr 2011, 14:59 UTC
Proton Hits and Hot Pixels
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At 16:16:08 UT on March 25, 2011 and again at 16:17:08 (see on left) bright flashes were seen in the lower left corner of images in the AIA He II 304 bandpass. There has been some speculation about the cause of these flashes. They are proton hits on the CCD that records the images in this telescope. As the proton moves through the CCD it ionizes the silicon and leaves electrons in its wake. Proton hits are a main cause of hot pixels or spikes in any space-based CCD. They are often seen in images recorded by the LASCO coronagraphs on SOHO. SDO instruments have shielding to keep the low energy protons out of the CCD, but as solar activity picks up the number of hits by high energy protons will increase. When you go to the original FITS data from 16:16:08, enlarge the image (left), and apply a rainbow color table that maps small values to blue and large values to red, you can see the some pixels with electrons caused by the proton before it slowed enough to have the large ionization signature. In these examples the number of electrons left behind is so large the CCD pixels ...

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