Mitigating Internal Instrument Coupling for 21 cm Cosmology. II. A Method Demonstration with the Hydrogen Epoch of Reionization Array

Abstract

2 Kern et al.We present a study of internal reflection and cross coupling systematics in Phase 1 of the Hydrogen Epoch of Reionization Array (HERA). In a companion paper, we outlined the mathematical formalism for such systematics and presented algorithms for modeling and removing them from the data. In this work, we apply these techniques to data from HERA's first observing season as a method demonstration. The data show evidence for systematics that, without removal, would hinder a detection of the 21 cm power spectrum for the targeted EoR line-of-sight modes in the range 0.2 < k < 0.5 h −1 Mpc. After systematic removal, we find we can recover these modes in the power spectrum down to the integrated noise-floor of a nightly observation, achieving a dynamic range in the EoR window of 10 −6 in power (mK 2 units) with respect to the bright galactic foreground signal. In the absence of other systematics and assuming the systematic suppression demonstrated here continues to lower noise levels, our results suggest that fully-integrated HERA Phase I may have the capacity to set competitive upper limits on the 21 cm power spectrum. For future observing seasons, HERA will have upgraded analog and digital hardware to better control these systematics in the field.

Detection of cosmic structures using the bispectrum phase. II. First results from application to cosmic reionization using the Hydrogen Epoch of Reionization Array

“…Both the data and the model have a central peak at κ k ¼ 0 pseudo h Mpc −1 and a noise floor at jκ k j ≳ 0.85 pseudo h Mpc −1 consistent with the model of foregrounds including noise (right). The data exhibit secondary peaks at κ k ≃ 0.5 pseudo h Mpc −1 , which have not been modeled in the right panel and are believed to be caused by baseline-dependent errors, such as cross-talk between pairs of antennas [92]. The values around these secondary peaks appear to be systematic-limited contrasting the rest of the bins where they are predominantly noise-limited.…”

“…The secondary peaks in the power spectrum arise due to a ∼1 MHz spectral ripple that can be seen in the visibility amplitude, phase, and closure phase spectra at a level of ∼0.5%, in the worst cases [71]. References [92,93] have also observed and modeled a very similar systematic effect in their data and they conclude that it is not an antenna-based but a baseline-dependent systematic such as cross-talk between antennas. The fact that bispectrum phases are immune to direction-independent and multiplicative antenna-based systematics therefore confirms that these secondary peaks probably arise from baselinedependent effects which could be some combination of interfeed or interdish cross-coupling along over-the-air or electrical pathways.…”

Understanding the HERA Phase I receiver system with simulations and its impact on the detectability of the EoR delay power spectrum

“…The analysis of the data obtained with 46 antennas closely packed are consistent with these simulations. These results are detailed in Kern et al (2020a). In particular, the system response is studied thanks to the interferometric visibility computed in the delay domain (cf.…”

Effects of model incompleteness on the drift-scan calibration of radio telescopes

“…Typically, in arrays like the JVLA, which are not equipped with Dicke switching radiometers, autocorrelations are usually not employed in calibration. However, responding to the challenge of calibrating on wide fields without signal loss/suppression (Patil et al 2016;Barry et al 2016), 21-cm experiments have used auto-correlations to calibrate signal chain reflections (Barry et al 2019;Li et al 2019;Kern et al 2019Kern et al , 2020a and to make an independent measure of absolute calibration (see e.g. HERA memo #34, Bowman et al 2007).…”