Updates to the SBC Dark Rate Monitor

TL;DR

This paper reports on expanded monitoring of the SBC dark rate, analyzing its behavior relative to temperature, the South Atlantic Anomaly, and detector regions, confirming the stability of the SBC-LODARK aperture for small sources.

Contribution

It provides updated analysis of SBC dark rate behavior with expanded data, assessing influences like SAA and detector regions, and confirms the stability of the SBC-LODARK aperture.

Findings

No significant correlation between SAA proximity and dark rate increases.

The SBC-LODARK aperture maintains low dark rates and is suitable for small sources.

Expanded calibration program improves dark rate monitoring and analysis.

Abstract

The Solar Blind Channel (SBC) typically exhibits elevated dark rate levels at temperatures exceeding 25.5{\deg}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.