I think that a lot of the noise in the CCD images are due to 'warm' (not hot) pixels. I have put together a short pdf discussion on this topic. If you hit the 'Attach' tab at the top of this page you should find it. But, maybe not.

or try clicking this link to view the PDF file: warm_pixels.pdf

--KenDere, 12-Jul-2007

Update:

In my write up on warm pixels on the eis wiki, I showed that it was possible to predict the locations of warm pixels and mark them to good accuracy. This was done from calibration files taken on the day previous to the observations.

Harry Warren has found that the warm pixel patterns change with time and looking at two calibration files taken 5 months apart, there was no resemblance between the two. This surprised me but it indicates that the warm pixel effect is not intrinsic to a given pixel. Nevertheless, it should be possible to calibrate them out.

So, I think we should be able to take care of the numerous warm pixels by obtaining daily calibration files. This could be done by taking a regcal014 and a regcal073 on a daily basis. It could be done during the XRT off-pointings with little to lose. It should be possible to make a shorter, single regcal that takes a 0s dark exposure and a 100s dark exposure of the full (512x 2048 x 2) CCD. Not sure I can make a dark exposure myself and my current IDL is not completely functional.

--KenDere, 18-Jul-2007