In this paper, we report new limits on 21cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. This work extends the work presented in Parsons et al. (2014) with more collecting area, a longer observing period, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optimal quadratic estimators. The result is a new 2σ upper limit on Δ2(k) of (22.4 mK)2 in the range 0.15<k<0.5hMpc−1 at z=8.4. This represents a three-fold improvement over the previous best upper limit. As we discuss in more depth in a forthcoming paper (Pober et al. 2015, in prep), this upper limit supports and extends previous evidence against extremely cold reionization scenarios. We conclude with a discussion of implications for future 21cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array (HERA). The limits presented in this paper have been retracted: The erratum can be found in Appendix A.
@article{arxiv.1502.06016,
title = {PAPER-64 Constraints on Reionization: The 21cm Power Spectrum at z=8.4},
author = {Zaki S. Ali and Aaron R. Parsons and Haoxuan Zheng and Jonathan C. Pober and Adrian Liu and James E. Aguirre and Richard F. Bradley and Gianni Bernardi and Chris L. Carilli and Carina Cheng and David R. DeBoer and Matthew R. Dexter and Jasper Grobbelaar and Jasper Horrell and Daniel C. Jacobs and Pat Klima and David H. E. MacMahon and Matthys Maree and David F. Moore and Nima Razavi and Irina I. Stefan and William P. Walbrugh and Andre Walker},
journal= {arXiv preprint arXiv:1502.06016},
year = {2018}
}