IRS-TR 11002: Calibration of the Acquisition Images from the Red Peak-Up   Sub-Array
  We present a calibration of the acquisition data obtained by the Red Peak-Up (PU) sub-array on the Infrared Spectrograph on Spitzer, based on repeated observations of three K giants. This calibration is tied directly to the most current infrared calibration based on data from Multiband Imaging Photometer for Spitzer. An analysis of the responsivity of the Red PU sub-array reveals no detectable deviations from linearity in the most recent pipeline version, but older pipeline versions show evidence suggesting possible small non-linearities. 
G. C. Sloan and D. A. Ludovici
astro-ph.IM