Hot Pixel

The hotpixel maps are made over temperatures ranging from -40 c to -120 c. The meanbiasclip tool is applied to 10 dark frame readouts to eliminate background x-ray events. This will also reject weakly flickering pixels for which there is as yet no evidence. Hotpixels can be marked by measuring relative to the rms deviation of the background, in this example a 10 sigma excess is flagged. This example taken at -75 c shows only a small number of hotpixels - most of which are not due to the radiation damage. As the temperature is decreased these remaining hotpixels vanish.The intensity of the hotpixels decreases as the "glow" of the radiated spot decreases so that the hotpixels may be considered the most extreme examples of an enhanced dark current which affects all pixels in the radiated area.Looking in more detail at the hotpixels it is easily seen that they are all "single events".Here is a closer look at the same hotpixel map. Notice that a number of pixels lie slightly below the 10 sigma threshold level. This is the same situation which affects the shuttle device hotpixel maps. The sacrificial charge pram can be used to help locate particularly strong traps, but at the present time none have been found. It should be noted that immediately following irradiation there is a much higher number of truly hot and flickering pixels but that after a period of time at room temperature these go away. At some point we should try to separate the radiation damage effects into the short term and those that persist.