CHIPS: THE COSMOLOGICAL H i POWER SPECTRUM ESTIMATOR

Trott, Cathryn M.; Pindor, B.; Procopio, P.; Wayth, R. B.; Mitchell, D. A.; McKinley, B.; Tingay, S. J.; Barry, N.; Beardsley, Adam P.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Oliveira-Costa, A. de; Dillon, Joshua S.; Ewall‐Wice, Aaron; Lü, Feng; Greenhill, L. J.; Hazelton, B. J.; Hewitt, Jacqueline N.; Hurley‐Walker, N.; Johnston‐Hollitt, M.; Jacobs, Daniel; Kaplan, D. L.; Kim, Han-Seek; Lenc, E.; Line, J.; Loeb, Abraham; Lonsdale, Colin J.; Morales, M. F.; Morgan, E.; Neben, Abraham R.; Thyagarajan, Nithyanandan; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Pober, Jonathan C.; Prabu, T.; Riding, J.; Shankar, N. Udaya; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Sullivan, M.; Tegmark, Max; Webster, R. L.; Williams, A.; Williams, Christopher; Wu, Chen; Wyithe, J. Stuart B.

doi:10.3847/0004-637x/818/2/139

Cited by 128 publications

(132 citation statements)

References 52 publications

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“…In our estimation of added contamination due to beam modelling errors, we overestimate the expected errors for the MWA EoR experiment. Both MWA EoR pipelines RTS/CHIPS (Mitchell et al 2008;Trott et al 2016) and FHD/ ppsilon (Sullivan et al 2012;Jacobs et al 2016;Barry et al 2019) incorporate direction dependent calibration. RTS/CHIPS uses information about broken dipoles explicitly to better model individual MWA tile beams.…”

Section: Discussionmentioning

confidence: 99%

Calibration and 21-cm power spectrum estimation in the presence of antenna beam variations

Joseph

Trott

Wayth

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Detecting a signal from the Epoch of Reionisation (EoR) requires an exquisite understanding of galactic and extra-galactic foregrounds, low frequency radio instruments, instrumental calibration, and data analysis pipelines. In this work we build upon existing work that aims to understand the impact of calibration errors on 21-cm power spectrum (PS) measurements. It is well established that calibration errors have the potential to inhibit EoR detections by introducing additional spectral features that mimic the structure of EoR signals. We present a straightforward way to estimate the impact of a wide variety of modelling residuals in EoR PS estimation. We apply this framework to the specific case of broken dipoles in Murchison Widefield Array (MWA) to understand its effect and estimate its impact on PS estimation. Combining an estimate of the percentage of MWA tiles that have at least one broken dipole (15%-40%) with an analytic description of beam errors induced by such dipoles, we compute the residuals of the foregrounds after calibration and source subtraction. We find that that incorrect beam modelling introduces bias in the 2D-PS on the order of ∼ 10 3 mK 2 h −3 Mpc −3 , which is on the order of current lowest limits. Determining the accuracy of both current beam models and direction dependent calibration pipelines is therefore crucial in our search for an EoR signal.

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Section: Discussionmentioning

confidence: 99%

Calibration and 21-cm power spectrum estimation in the presence of antenna beam variations

Joseph

Trott

Wayth

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The longer baselines will also allow for deeper measurements of foreground sources due to the reduced classical confusion limit, expanding the foreground catalogue by a factor of 3 -4. Using a model of extragalactic foreground contamination similar to that of Trott et al (2016), this could reduce the amount of leaked foreground power by an estimated factor of 10 2 -10 3 .…”

Section: Lobes and Diffuse Emissionmentioning

confidence: 99%

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Beardsley

Johnston‐Hollitt

Trott

et al. 2019

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low frequency (80-300 MHz) southern sky. Since beginning operations in mid 2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together 60+ programs recorded 20,000 hours producing 146 papers to date. In 2016 the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper we review the major results from the prior operation of the MWA, and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes, but also include ideas for directions outside these categories.

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“…We do not consider deconvolution in this paper. It is common to subtract bright sources before the gridding step (Beardsley et al 2016;Patil et al 2017;Trott et al 2016). Gridding consists of discretizing the non-uniformly sampled u, v, w values.…”

Section: Griddingmentioning

confidence: 99%

“…Interferometric experiments aim to detect the EoR signals through power spectrum analysis (Paciga et al 2013;Beardsley et al 2016;Patil et al 2017;Trott et al 2016). Such analysis can combine a large field of view and several MHz of bandwidth to decrease the uncertainty due to the thermal noise of the instrument to ultimately detect the signals from the EoR in a statistical manner.…”

Section: Introductionmentioning

confidence: 99%

Precision requirements for interferometric gridding in the analysis of a 21 cm power spectrum

Offringa

Mertens

Tol

et al. 2019

A&A

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Context. Experiments that try to observe the 21-cm redshifted signals from the Epoch of Reionization using interferometric lowfrequency instruments have stringent requirements on the processing accuracy. Aims. We analyse the accuracy of radio interferometric gridding of visibilities with the aim to quantify the power spectrum bias caused by gridding, ultimately to determine the suitability of different imaging algorithms and gridding settings for 21-cm power spectrum analysis. Methods. We simulate realistic Low-Frequency Array (LOFAR) data, and construct power spectra with convolutional gridding and w-stacking, w-projection, image domain gridding and without w-correction. These are compared against directly Fourier transformed data. The influence of oversampling, kernel size, w-quantization, kernel windowing function and image padding are quantified. The gridding excess power is measured with a foreground subtraction strategy, for which foregrounds have been subtracted using Gaussian progress regression, as well as with a foreground avoidance strategy. Results. Constructing a power spectrum that has a bias significantly lower compared to the expected EoR signals is possible with the tested methods, but requires a kernel oversampling factor of at least 4000 and, when using w-correction, at least 500 w-quantization levels. These values are higher than typical values used for imaging, but are computationally feasible. The kernel size and padding factor parameters are less crucial. Among the tested methods, image domain gridding shows the highest accuracy with the lowest imaging time.Conclusions. LOFAR 21-cm power spectrum results are not affected by gridding. Image domain gridding is overall the most suitable algorithm for 21-cm Epoch of Reionization power spectrum experiments, including for future Square Kilometre Array (SKA) EoR analyses. Nevertheless, convolutional gridding with tuned parameters results in sufficient accuracy for interferometric 21-cm Epoch of Reionization experiments. This holds also for w-stacking for wide-field imaging. The w-projection algorithm is less suitable because of the kernel oversampling requirements, and a faceting approach is unsuitable due to the resulting spatial discontinuities.

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CHIPS: THE COSMOLOGICAL H i POWER SPECTRUM ESTIMATOR

Cited by 128 publications

References 52 publications

Calibration and 21-cm power spectrum estimation in the presence of antenna beam variations

Calibration and 21-cm power spectrum estimation in the presence of antenna beam variations

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Precision requirements for interferometric gridding in the analysis of a 21 cm power spectrum

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