MITEoR: a scalable interferometer for precision 21 cm cosmology

Abstract

We report on the MIT Epoch of Reionization (MITEoR) experiment, a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce the cost of the high-sensitivity 3D mapping required for 21 cm cosmology. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction. We demonstrate and quantify the power and robustness of redundancy for scalability and precision. We find that the calibration parameters precisely describe the effect of the instrument upon our measurements, allowing us to form a model that is consistent with χ 2 per degree of freedom < 1.2 for as much as 80% of the observations. We use these results to develop an optimal estimator of calibration parameters using Wiener filtering, and explore the question of how often and how finely in frequency visibilities must be reliably measured to solve for calibration coefficients. The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious Hydrogen Epoch of Reionization Array (HERA) project and other next-generation instruments, which would incorporate many identical or similar technologies.

PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM ATz= 8.4

“…The grid-based configuration of PAPER antennas allows a large number of antenna calibration parameters to be solved for on the basis of redundancy (P12a; P14; Zheng et al 2014). Multiple baselines of the same length and orientation measure the same sky signal.…”

“…In practice, redundant calibration often takes on two flavors: log calibration (LOGCAL) and linear calibration (LINCAL) (Liu et al 2010;Zheng et al 2014). LOGCAL uses logarithms applied to visibilities,…”

“…Using initial estimates taken from LOGCAL, LINCAL constructs an unbiased estimator. Redundant calibration was performed using OMNICAL 17 an open-source redundant calibration package that is relatively instrument agnostic (Zheng et al 2014). This package implements both LOGCAL and LINCAL, solving for a complex gain solution per antenna, frequency, and integration.…”

“…These configurations are poorly suited for synthesis imaging but deliver a substantial sensitivity boost for power-spectral measurements that are not yet limited by cosmic variance (Parsons et al 2012a, hereafter P12a). Moreover, they are particularly suited for redundancy-based calibration (Wieringa 1992;Liu et al 2010;Zheng et al 2014), on which PAPER now relies to solve for the majority of the internal instrumental degrees of freedom (dof). The efficacy of this approach was demonstrated with data from a 32-antenna deployment of PAPER, which achieved an upper limit on the 21 cm power spectrum Δ 2 (k) ⩽ (41 mK) 2 at k h 0.27 Mpc 1 = - (Parsons et al 2014, hereafter P14).…”

Optimized Beam Sculpting With Generalized Fringe-Rate Filters

“…These differences have led to the design, construction, and usage of new interferometers that only have moderate angular resolution, but are comprised of a large number of receiving elements with wide fields of view operating over a wide bandwidth. Examples of new interferometers that broadly fit some or all of this description include the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; Parsons et al 2010), the Murchison Widefield Array (MWA; Tingay et al 2013;Bowman et al 2013), the LOw Frequency ARray (LOFAR; van Haarlem et al 2013), the Canadian Hydrogen Intensity Mapping Experiment (CHIME; Bandura et al 2014), the MIT Epoch of Reionization experiment (MITEoR; Zheng et al 2014), the Large Aperture Experiment to Detect the Dark Ages (LEDA; Greenhill & Bernardi 2012), and the Hydrogen Epoch of Reionization Array (HERA; Pober et al 2014). Further deviating from conventional array designs, the PAPER, MITEoR, CHIME, HERA projects have also maximized sensitivity by choosing to place their antenna elements in regular, redundant grids (Parsons 1 Astronomy Dept., U. California, Berkeley, CA 2 Radio Astronomy Lab., U. California, Berkeley, CA 3 Berkeley Center for Cosmological Physics, Berkeley, CA et al 2012a).…”