Recover additional information from HCO telecommunications RFI bands

Investigate whether further improvements to the HCO calibration and RFI-filtering pipeline can recover astrophysical information in the 625–650 MHz and 730–770 MHz bands, whose noise properties remain inconsistent with thermal statistics after applying the Karhunen–Loève filter.

Background

The radiometer test finds that the 625–650 MHz and 730–770 MHz telecommunications bands remain dominated by non-thermal statistics, even after applying the Karhunen–Loève transform filter. The authors identify several possible causes, including incorrect interpolated gain solutions, insufficient East–West angular resolution for constraining the RFI direction, quantization saturation, or non-stationary RFI on millisecond timescales.

Because these channels may still contain transient astrophysical signals, determining whether improved calibration or site-specific RFI-filtering methods can recover them is an explicitly unresolved technical problem. The question is directly tied to extending HCO’s usable bandwidth beyond the channels retained in the present analysis.

References

This suggests that the failure to recover these channels using HCO is likely site specific (e.g., incorrect gains, lack of East-West resolution to constrain the direction of the RFI) and work is currently underway to investigate whether further improvements can be made to recover information in these channels.

— The CHIME/FRB Outriggers: Commissioning the Hat Creek Outrigger and an Updated Calibration Scheme for Mitigating RFI  (2609.10686 - Lazda et al., 9 Sep 2026) in Section “Radiometer Test” (label ss:radiometer_test)