NOTE: This delivery also includes additional pmasks for the warm mission. This will include any pmask dated later than May 2009. Since the number of bad pixels changed markedly at the warmer temperature, it is important not to mix masks between the warm and cryogenic periods.

Pmasks were made at intervals of several months, with reduced frequency later in the mission as the variation in bad pixels is seen to be small.

The masks were created by taking darks and flats from five campaigns close to the epoch indicated in the mask name (the exception to this are the January 2005 and February 2005 mask sets which were made from data either side of a solar storm at the end of January 2005). Noise (RMS) images were made from the data in each dark and flat AOR, using object masking to exclude pixels contaminated by stars and galaxies. Noisy pixels with values more than twice the median in the RMS images are flagged. In addition, pixels with less than 1/3 the median responsivity and with abnormally low (0.01x) median noise level are flagged as dead. Pixels persistently turned on are flagged as hot. In order to be included in the pmask, these pixels must have been flagged consistently in all five input darks and flats. Images of persistently saturated pixels in the darks were also made (though in practice none have been found so far), along with masks for the amplifier glow in channels 3 and 4 (derived from pre-flight data). Bits were then set in the pmasks as follows:

Other keywords in the header give the exact timeranges over which the pmasks are valid both in spacecraft clock time (SCLKSTRT and SCLKEND) and in UT (STRTDATE, ENDDATE).

Note that these pmask sets supercede previous versions, which were typically more aggressive (but also less consistent). In this set only bad pixels persistent over five or more campaigns are masked.

Supermasks

In addition to the epochal pmask sets, we have constructed two sets of pmasks based on all the epochs. The "ormasks" consist of all the bad pixels ever recorded in a given channel throughout the cryogenic or warm missions, respectively, flagged with bits 7,8,9,10 or 14. The "andmasks" consist of only those pixels present in all the pmasks (during the cryogenic or warm missions) in a given channel flagged with 7,8,9,10 or 14. Only bit 0 is used for these masks as the bad pixels are combined irrespective of their origin. The warm mission supermasks have the word "warm" in the file name.

PMask Fatal Bit Patterns in MOPEX

PMask_Fatal_BitPattern = 32767 (take into account all set bits)

If you have high background observations (probably all 30 second and higher frametimes, and shorter frametimes close to the Ecliptic plane), you probably do not need to mask the amplifier glow (bit 10) in channel 3 and 4 pmasks, giving a fatal bit pattern of 31743.

NOTE: All the pmasks given in this new package are in BCD orientation and therefore no flipping is required.

Download IRAC pmask files (updated 18 Feb 2020) (Tar File, 100 KB)

Please read the included README file carefully and note which set of pmasks to use so that you use the set that is applicable to the date when your observations were taken.