Using Cosmic Rays detected by HST as Geophysical Markers I: Detection and Characterization of Cosmic Rays

TL;DR

This study analyzes over 1.2 billion cosmic rays detected by the Hubble Space Telescope over 30 years, revealing solar modulation effects, energy estimates, and regional flux variations, and provides a new Python tool for cosmic ray analysis.

Contribution

The paper introduces a comprehensive analysis of HST cosmic ray data and a new Python package, exttt{HSTcosmicrays}, for community use, with detailed modeling and regional flux findings.

Findings

Cosmic ray flux modulated by solar activity.

Estimated typical cosmic ray energy at 534 ± 117 MeV.

Identified regional flux enhancements over North America and Australia.

Abstract

The Hubble Space Telescope (HST) has been operational for over 30 years and throughout that time it has been bombarded by high energy charged particles colloquially referred to as cosmic rays. In this paper, we present a comprehensive study of more than 1.2 billion cosmic rays observed with HST using a custom written python package, \texttt{HSTcosmicrays}, that is available to the astronomical community. We analyzed $75,908$ dark calibration files taken as part of routine calibration programs for five different CCD imagers with operational coverage of Solar Cycle 23 and 24. We observe the expected modulation of galactic cosmic rays by solar activity. We model the observed energy-loss distributions to derive an estimate of 534 $\pm$ 117 MeV for the kinetic energy of the typical cosmic ray impacting HST. For the three imagers with the largest non-uniformity in thickness, we independently confirm the overall structure produced by fringing analyses by analyzing cosmic ray strikes across the detector field of view. We analyze STIS/CCD observations taken as HST crosses over the South Atlantic Anomaly and find a peak cosmic-ray particle flux of $\sim1100$ $particle/s/cm^2$. We find strong evidence for two spatially confined regions over North America and Australia that exhibit increased cosmic-ray particle fluxes at the $5\sigma$ level.