The effects of cosmic rays and solar flares on the IRAC detectors: the first two years of in-flight operation

The Infrared Array Camera (IRAC) is a four-channel camera on the Spitzer Space Telescope, one of three focal plane science instruments. IRAC uses two pairs of 256x256 pixel InSb and Si:As IBC detectors to provide simultaneous imaging at 3.6, 4.5, 5.8, and 8 microns. IRAC experiences a flux of cosmic rays and solar protons that produce transient effects in science images from each of the arrays, with 4-6 pixels per second being affected during each integration. During extreme solar flares, IRAC experiences a much higher rate of transients which affects the science data quality. We present cosmic ray rates and observed detector characteristics for IRAC during the first two years of science operation, and rates observed in a period of elevated solar proton flux during an intense solar flare in January 2005. We show the changes to the IRAC detectors observed since launch, and assess their impacts to the science data quality.