Mitigating Internal Instrument Coupling for 21 cm Cosmology. I. Temporal and Spectral Modeling in Simulations

Abstract

We study the behavior of internal signal chain reflections and antenna cross coupling as systematics for 21 cm cosmological surveys. We outline the mathematics for how these systematics appear in interferometric visibilities and describe their phenomenology. We then describe techniques for modeling and removing these systematics without attenuating the 21 cm signal in the data. This has critical implications for low-frequency radio surveys aiming to characterize the 21 cm signal from the Epoch of Reionization and Cosmic Dawn, as systematics can cause bright foreground emission to contaminate the EoR window and prohibit a robust detection. We also quantify the signal loss properties of the systematic modeling algorithms, and show that our techniques demonstrate resistance against EoR signal loss. In a companion paper, we demonstrate these methods on data from the Hydrogen Epoch of Reionization Array as a proof-of-concept.

Redundant-baseline calibration of the hydrogen epoch of reionization array

“…The legacy PAPER components are all now being replaced as construction on the full HERA system continues through 2020. This work complements other recent work with HERA on both systematics mitigation (Kern et al 2019c;Kern et al 2019a) and sky-based calibration and (post-redundant) absolute calibration (Kern et al 2019b). Likewise, this paper complements the investigation of the spectral smoothness of HERA's calibration solutions in Kern et al (2019b) with an investigation of the temporal structure of those solutions and its origin.…”

“…We see clear evidence for non-redundancy at a level comparable to the fiducial ∼10% error level in Orosz et al (2019), so this concern appears to be pressing. However, it does not appear to be the leading-order contribution to unsmooth gains; Kern et al (2019b) shows clear evidence for spurious spectral structure in HERA's solved gains using both sky-based and redundant-baseline calibration attributable to cross-coupling systematics (Kern et al 2019c;Kern et al 2019a). As was suggested in the conclusion of Orosz et al 2019, Kern et al (2019b) demonstrate that low-pass filtering of calibration solutions appears to be a robust way of mitigating this effect.…”

Constraining the intergalactic medium at z ≈ 9.1 using LOFAR Epoch of Reionization observations

“…This then requires exquisite calibration of the system as any left-over artefacts from strong sources will make a measurement impossible (Barry et al 2016;Patil et al 2017). This implies calibrating the many hardware components of the telescope (see e.g., Kern et al 2019) while a further complication is added by the presence of the temporally and spatially varying ionosphere (see e.g., Mevius et al 2016).…”

“…Moreover, an exquisite calibration of the system is required to minimize the artefacts from strong sources (Barry et al 2016;Patil et al 2017), and a long observation time is necessary to reduce the instrumental noise. Further calibration challenges may be posed by the hardware components of the telescope (see e.g., Kern et al 2019) and by the temporally and spatially varying ionosphere (see e.g., Mevius et al 2016), to mention a few.…”

DAYENU: a simple filter of smooth foregrounds for intensity mapping power spectra

“…Perhaps most glaring is the fact that C not actually known to much precision. The low-level component from the 21-cm signal itself is completely unknown while our ability to characterize our instrument (Pober et al 2012;Neben et al 2015Neben et al , 2016Jacobs et al 2017;Fagnoni et al 2019) and low-frequency foregrounds (Jacobs et al 2011;Carroll et al 2016;Line et al 2017;Zheng et al 2017;Eastwood et al 2018) is currently limited to the ∼1 per cent level.…”