IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
that. Also, the cosmic ray flux is normally about a factor of two higher on average around solar minimum
compared with solar maximum. Radiation hits do increase suddenly and dramatically during some major
solar proton events. Historically, several such events have occurred over the course of the active part of a
Solar cycle.
Two major solar proton events occurred during IOC, so we have experience in identifying them and their
effects. Because of shielding around the instruments, only extremely energetic protons (> 100 MeV) of
any origin appear as cosmic ray hits in the data. Thus, many solar weather phenomena (“storms," etc.)
which do occasionally affect other spacecraft, or ground systems, are not of concern to Spitzer.
Radiation has very little effect on the IRAC arrays beyond elevating the counts in a given pixel. Some
high energy cosmic rays cause persistent images, column pull-down, and muxbleed effects.
Data Features and Artifacts 133 Cosmic Rays and Solar Protons