ACIS Bad Pixel List

Updated: 2026-08-24 (DOY: 236)

Combined Front Side CCD and Column History Plots (Click to Enlarge)

Previously unknown bad pixels/columns appeared in the last 14 days:

Current Bad Pixels/Columns

more than 70% of the time in the last two weeks, the pixel is listed as a warm pixel.

If a "warm" pixel candidate shows up more than 30% but less than 70% of the time in the last two weeks, the pixel is listed as a flickering pixel.

If the pixels which appeared in "current warm pixels" list, even once in the past the pixels are parmanently listed in "Past Warm Pixels" list.

Hot pixels are defined as warm pixels with an adu value of greater than the CCD average +1000.

If the pixel was located at the edge of the CCD (y = 1023, 1024), it is ignored and not included on either the list.

For a hot pixel, a process was same, except a threshold was a ccd average plus 1000 counts.

A bad column was selected as follows:

• each column was averaged out, and compared to an average for an entire ccd.
• If the average of the column was 5 sigma higher than the average of the ccd compare the column average to a local average (10 columns).
• If the column was still 5 sigma higher than the local average, mark it as a bad column candidate.
• If a "warm" column candidate shows up more than 70% of the time in the last two weeks, it is listed as a warm columns.
• If a "warm" column candidate shows up more than 30% but less than 70% of the time in the last two weeks, it is listed as a flickering columns.

If you have any quesitons about this page, please contact swolk@cfa.harvard.edu.