Origin of the solar-cycle phase lag in Hubble radiation damage

Determine whether the approximately 430-day lag between the Solar activity proxy and the radiation damage measured in the Hubble Space Telescope's Advanced Camera for Surveys/Wide Field Channel reflects a phase difference in Solar physics between the production of energetic particles and sunspots, or a local delay caused by the Earth's magnetic field.

Background

The paper analyzes the time evolution of charge-trap density in the Hubble Space Telescope's CCD detectors and finds that the maximum rate of radiation damage occurs approximately 4.3 years before Solar maximum. A sunspot-based model fits the observations with a fitted lag of approximately 430 days, but the physical origin of this delay is unresolved.

Two possible explanations are identified: the lag may arise from a phase offset in Solar physics between sunspot activity and the production of energetic particles, or it may be produced locally as particles propagate through or are modulated by the Earth's magnetic field. Resolving this distinction is important for developing physically predictive models of radiation damage in Low Earth Orbit rather than merely empirical fits.