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Trend of the XIS NXB from night Earth data, extracting a 512x512 box from the chip center, using only COR2>6 data with normal SCI on (XIS1 at 2 keV level). XIS1 has a clear downward slope of -0.003 cts/s/yr +/- 20%, or about 3% per year. XIS0,3 are consistent with no change. Perhaps this is actually a gain issue with XIS1.
Look at the PDF also.
Update post-meeting: Now including all COR2, 5-15 keV (to reduce gain effects around 7 keV). XIS1 still changes by 4% +/- 1% per year, though with lots of scatter. +/-1-sigma limits for FIs: +0%/-1% (XIS0), +0.5%/-0.5% (XIS3).
Look at the PDF also.
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