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  • 1
    Language: English
    In: Quick submit: 2017-02-13T20:44:11-0500
    Description: We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 104 mK on comoving scales k≲0.5hMpc−1. This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12≲z≲18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.
    Keywords: Dark Ages, Reionization, First Stars ; Techniques: Interferometric ; Radio Lines: General ; X-Rays: Galaxies
    ISSN: Ewall-Wice, A., Joshua S. Dillon, J. N. Hewitt, A. Loeb, A. Mesinger, A. R. Neben, A. R. Offringa, et al. 2016. “First Limits on the 21 Cm Power Spectrum During the Epoch of X-Ray Heating.” Monthly Notices of the Royal Astronomical Society 460 (4) (May 19): 4320–4347. doi:10.1093/mnras/stw1022.
    ISSN: 0035-8711
    Source: Harvard University Library
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  • 2
    Language: English
    In: Quick submit: 2017-02-13T20:05:44-0500
    Description: The Detection of redshifted 21 cm emission from the epoch of reionization (EoR) is a challenging task owing to strong foregrounds that dominate the signal. In this paper, we propose a general method, based on the delay spectrum approach, to extract HI power spectra that is applicable to tracking observations using an imaging radio interferometer (Delay Spectrum with Imaging Arrays (DSIA)). Our method is based on modelling the HI signal taking into account the impact of wide field effects such as the w-term which are then used as appropriate weights in cross-correlating the measured visibilities. Our method is applicable to any radio interferometer that tracks a phase center and could be utilized for arrays such as MWA, LOFAR, GMRT, PAPER and HERA. In the literature the delay spectrum approach has been implemented for near-redundant baselines using drift scan observations. In this paper we explore the scheme for non-redundant tracking arrays, and this is the first application of delay spectrum methodology to such data to extract the HI signal. We analyze 3 hours of MWA tracking data on the EoR1 field. We present both 2-dimensional (k∥,k⊥) and 1-dimensional (k) power spectra from the analysis. Our results are in agreement with the findings of other pipelines developed to analyse the MWA EoR data.
    Keywords: Cosmology: Observations ; Cosmology: Theory ; Dark Ages ; Reionization ; First Stars ; Techniques: Interferometric
    ISSN: Paul, Sourabh, Shiv K. Sethi, Miguel F. Morales, K. S. Dwarkanath, N. Udaya Shankar, Ravi Subrahmanyan, N. Barry, et al. 2016. Delay Spectrum with Phase-Tracking Arrays: Extracting the HI power spectrum from the Epoch of Reionization. The Astrophysical Journal 833 (2) (December 19): 213. doi:10.3847/1538-4357/833/2/213.
    ISSN: 1538-4357
    Source: Harvard University Library
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  • 3
    Language: English
    In: Quick submit: 2017-02-13T20:42:24-0500
    Description: We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds.
    Keywords: Cosmology: Dark Ages, Reionization, First Stars ; Methods: Data Analysis ; Techniques: Interferometric
    ISSN: Jacobs, Daniel C., B. J. Hazelton, C. M. Trott, Joshua S. Dillon, B. Pindor, I. S. Sullivan, J. C. Pober, et al. 2016. “The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology.” The Astrophysical Journal 825 (2) (July 11): 114. doi:10.3847/0004-637x/825/2/114.
    ISSN: 1538-4357
    Source: Harvard University Library
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  • 4
    Language: English
    In: Quick submit: 2017-02-13T20:12:04-0500
    Description: The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hours of MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of Δ2≤2.7×104 mK2 at k=0.27 h~Mpc−1 and z=7.1, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis we have identified a list of improvements to be made to our EoR data analysis strategies. These improvements will be implemented in the future and detailed in upcoming publications.
    ISSN: Beardsley, A. P., B. J. Hazelton, I. S. Sullivan, P. Carroll, N. Barry, M. Rahimi, B. Pindor, et al. 2016. “FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7.” The Astrophysical Journal 833 (1) (December 9): 102. doi:10.3847/1538-4357/833/1/102.
    ISSN: 1538-4357
    Source: Harvard University Library
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  • 5
    Language: English
    In: Quick submit: 2017-02-13T22:39:01-0500
    Description: Detection of the cosmological neutral hydrogen signal from the Epoch of Reionization, and estimation of its basic physical parameters, is the principal scientific aim of many current low-frequency radio telescopes. Here we describe the Cosmological HI Power Spectrum Estimator (CHIPS), an algorithm developed and implemented with data from the Murchison Widefield Array (MWA), to compute the two-dimensional and spherically-averaged power spectrum of brightness temperature fluctuations. The principal motivations for CHIPS are the application of realistic instrumental and foreground models to form the optimal estimator, thereby maximising the likelihood of unbiased signal estimation, and allowing a full covariant understanding of the outputs. CHIPS employs an inverse-covariance weighting of the data through the maximum likelihood estimator, thereby allowing use of the full parameter space for signal estimation ("foreground suppression"). We describe the motivation for the algorithm, implementation, application to real and simulated data, and early outputs. Upon application to a set of 3 hours of data, we set a 2σ upper limit on the EoR dimensionless power at k=0.05~h.Mpc−1 of Δ2k〈7.6×104~mK2 in the redshift range z=[6.2−6.6], consistent with previous estimates.
    Keywords: Techniques: Interferometric ; Early Universe
    ISSN: Trott, Cathryn M., Bart Pindor, Pietro Procopio, Randall B. Wayth, Daniel A. Mitchell, Benjamin McKinley, Steven J. Tingay et al. "CHIPS: The Cosmological H i Power Spectrum Estimator." The Astrophysical Journal 818, no. 2 (2016): 139. doi: 10.3847/0004-637X/818/2/139
    ISSN: 0004-637X
    Source: Harvard University Library
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