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Updates to the SBC Dark Rate Monitor

Alyssa M. Guzman, Roberto J. Avila

Abstract

The Solar Blind Channel (SBC) typically exhibits elevated dark rate levels at temperatures exceeding 25.5°C. However, instances of rapid dark rate increases have been observed before the detector reaches this threshold. To more closely monitor these anomalies, the existing calibration program was expanded, scheduling 24 total orbits per year distributed across eight visits for Cycle 31 and beyond. With enhanced data availability, we provide further updates and analysis of the dark rate in this report. We investigated the influence of the South Atlantic Anomaly (SAA) passage on dark rates. Using orbital parameters from SPT products, we plotted the Hubble Space Telescope's (HST) locations during dark exposures relative to the SAA. Comparison of HST paths during elevated and stable dark rate visits revealed no significant correlation between proximity to the SAA boundary and dark rate increases. Furthermore, we examined the stability of dark rates in the vicinity of the SBC-LODARK aperture within the detector. Our findings confirm that this region maintains consistently low dark rates across visits, unaffected by the elevated dark current observed elsewhere in the detector. The SBC-LODARK aperture therefore continues to be recommended for small sources.

Updates to the SBC Dark Rate Monitor

Abstract

The Solar Blind Channel (SBC) typically exhibits elevated dark rate levels at temperatures exceeding 25.5°C. However, instances of rapid dark rate increases have been observed before the detector reaches this threshold. To more closely monitor these anomalies, the existing calibration program was expanded, scheduling 24 total orbits per year distributed across eight visits for Cycle 31 and beyond. With enhanced data availability, we provide further updates and analysis of the dark rate in this report. We investigated the influence of the South Atlantic Anomaly (SAA) passage on dark rates. Using orbital parameters from SPT products, we plotted the Hubble Space Telescope's (HST) locations during dark exposures relative to the SAA. Comparison of HST paths during elevated and stable dark rate visits revealed no significant correlation between proximity to the SAA boundary and dark rate increases. Furthermore, we examined the stability of dark rates in the vicinity of the SBC-LODARK aperture within the detector. Our findings confirm that this region maintains consistently low dark rates across visits, unaffected by the elevated dark current observed elsewhere in the detector. The SBC-LODARK aperture therefore continues to be recommended for small sources.
Paper Structure (10 sections, 13 figures, 2 tables)

This paper contains 10 sections, 13 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data
  3. Updates on Dark Rate
  4. South Atlantic Anomaly Passage
  5. Low Dark and High Dark Regions
  6. Conclusion
  7. Acknowledgements
  8. Appendix

Figures (13)

  • Figure 1: All the dark rate measurements over time. Each data point corresponds to the dark rate of a dark image during a visit. The red highlighted data represents the discarded visits not used for our analysis. The cyan highlighted data represents the most recent visit.
  • Figure 2: The dark rate measurements over time, when the temperature of the detector was below 25.5° C. Each data point corresponds to the dark rate of a dark image during a visit. The cyan highlighted data represents the most recent visit.
  • Figure 3: The top panel shows the relationship between the dark rate and temperature and the bottom panel shows the relationship between the temperature and elapsed time from when the detector was turned on. The dashed lines represent the latest visit and the most recent elevated visits are shown in different colors for both panels. The stable visits are plotted in grey.
  • Figure 4: This plot shows the relationship between dark rate and the elapsed time after the detector has been turned on. The dashed lines represent the latest visit and the most recent elevated visits are shown in different colors for both panels. The stable visits are all plotted in grey.
  • Figure 5: The location of HST during the non-elevated 2023-12-11 visit.
  • ...and 8 more figures