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We investigate differences in Spitzer/IRAC 3.6 and 4.5micron photometry thatdepend on observing strategy. Using archival calibration data we perform anin-depth examination of the measured flux densities ("fluxes") of tencalibration stars, observed with all the possible observing strategies. We thenquantify differences in the measured fluxes as a function of 1) array mode(full or subarray), 2) exposure time, and 3) dithering versus staringobservations. We find that the median fluxes measured for sources observedusing the full array are 1.6% and 1% lower than those observed with thesubarray at [3.6] and [4.5], respectively. Additionally, we found a dependenceon the exposure time such that for [3.6] observations the long frame times aremeasured to be lower than the short frame times by a median value of 3.4% infull array and 2.9% in subarray. For [4.5] observations the longer frame timesare 0.6% and 1.5% in full and subarray respectively. These very smallvariations will likely only affect science users who require high-precisionphotometry from multiple different observing modes. We find no statisticallysignificant difference for fluxes obtained with dithered and staring-modes.When considering all stars in the sample, the fractional well depth of thepixel is correlated with the different observed fluxes. We speculate the causeto be a small non-linearity in the pixels at the lowest well depths wheredeviations from linearity were previously assumed to be negligible.

Warm Spitzer IRAC Photometry: dependencies on observing mode and exposure time