IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
Figure 7.20: The central 128x128 pixels of IRAC 12-second images taken on January 20, 2005 during a major
solar proton event. Channels 1 and 2 are top left and top right; channels 3 and 4 are bottom left and bottom
right. Except for the bright star in channels 1 and 3, almost every other source in these images is a cosmic
ray. These data are from observati ons in pi d 3126.
Cosmic rays for channels 3 and 4 are larger and affect more pixels than the channel 1 and 2 cosmic rays
due to the larger width of the active layer of the Si:As detectors. Some tuning of cosmic ray detection
parameters may be necessary when working with deep integrations, especially for channels 3 and 4.
Each IRAC array receives approximately 1.5 cosmic ray hits per second, with ~ 2 pixels per hit affected
in channels 1 and 2, and ~ 6 pixels per hit affected in channels 3 and 4. The cosmic ray flux varies
randomly by up to a factor of a few over time scales of minutes but does not undergo increases larger than
Data Features and Artifacts 132 Cosmic Rays and Solar Protons