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  • 1
    Language: English
    In: Nature, December 2018, Vol.564(7736), pp.E35
    Description: [...]their choice to use it over the full band was not justified. Judd D. Bowman1·, Alan E. E. Rogers2, Raul A. Monsalve1'3'4'5'6, Thomas J. Mozdzen1 & Nivedita Mahesh1 1School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA. 2Haystack Observatory, Massachusetts Institute of Technology, Westford, MA, USA. 3Department of Physics, McGill University, Montréal, Quebec, Canada. 4McGill Space Institute, McGill University, Montréal, Quebec, Canada. 5Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO, USA. 6Facultad de Ingeniería, Universidad Católica de la Santísima Concepción, Concepción, Chile. *e-mail: judd.bowman@asu.edu Published online 19 December 2018. First results on the epoch of reionization from first light with SARAS 2.
    Keywords: United States–Us ; Massachusetts ; Canada ; Quebec Canada ; Arizona ; Chile ; Space Exploration ; Astronomy ; Ionization ; Astronomy ; Calibration ; Astrophysics ; Ionosphere ; Space Exploration ; Parameter Estimation ; Massachusetts Institute of Technology ; Arizona State University ; University of Colorado ; Mcgill University;
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    In: Nature, 2014, Vol.506(7487), p.163
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 3
    Language: English
    In: Nature, Dec 9, 2010, Vol.468(7325), p.796(3)
    Description: Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies (1). The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (〉100K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources (2). If reionization happened rapidly, there should be a characteristic signature (2-4) visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 〈 z 〈 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of [DELTA]z 〈 0.06 at the 95% confidence level.
    Keywords: Hydrogen -- Research ; Brightness (Photometry) -- Research ; Radiation (Physics) -- Research
    ISSN: 0028-0836
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  • 4
    In: Nature, 2010, Vol.468(7325), p.796
    Description: Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies1. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (〉100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature2, 3, 4 visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 〈 z 〈 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of Δz 〈 0.06 at the 95% confidence level.
    Keywords: Sciences (General) ; Physics;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 5
    In: Nature, 2018, Vol.555(7694), p.67
    Description: After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz. Here we report the detection of a flattened absorption profile in the sky-averaged radio spectrum, which is centred at a frequency of 78 megahertz and has a best-fitting full-width at half-maximum of 19 megahertz and an amplitude of 0.5 kelvin. The profile is largely consistent with expectations for the 21-centimetre signal induced by early stars, however, the best-fitting amplitude of the profile is more than a factor of two greater than the largest predictions. This discrepancy suggests that either the primordial gas was much colder than expected or the background radiation temperature was hotter than expected. Astrophysical phenomena (such as radiation from stars and stellar remnants) are unlikely to account for this discrepancy, of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude. The low-frequency edge of the observed profile indicates that stars existed and had produced a background of Lyman-alpha photons by 180 million years after the Big Bang. The high-frequency edge indicates that the gas was heated to above the radiation temperature less than 100 million years later. Comment: Accepted version of article published March 1, 2018. Full edited version available through Nature Springer SharedIt at: http://rdcu.be/H0pE
    Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Instrumentation And Methods For Astrophysics;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 6
    Language: English
    In: Nature, Feb 13, 2014, Vol.506(7487), p.163(2)
    Description: Simulations of the cosmos cast doubt on assumptions about the temperature of primordial hydrogen gas when it was ionized by the first stars and galaxies, complicating the interpretation of ongoing observations. SEE LETTER P.197
    Keywords: Hydrogen – Properties ; Ionization – Research ; X-Ray Astronomy – Research ; Simulation – Research
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 7
    Language: English
    In: Monthly Notices of the Royal Astronomical Society, Jan, 2012, Vol.419(2), p.1070(15)
    Description: To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2966.2011.19766.x Byline: Geraint J. A. Harker (12★), Jonathan R. Pritchard (3), Jack O. Burns (12), Judd D. Bowman (4) Keywords: methods: statistical; cosmology: theory; diffuse radiation; radio lines: general Abstract: ABSTRACT Efforts are being made to observe the 21-cm signal from the 'cosmic dawn' using sky-averaged observations with individual radio dipoles. In this paper, we develop a model of the observations accounting for the 21-cm signal, foregrounds and several major instrumental effects. Given this model, we apply Markov Chain Monte Carlo techniques to demonstrate the ability of these instruments to separate the 21-cm signal from foregrounds and quantify their ability to constrain properties of the first galaxies. For concreteness, we investigate observations between 40 and 120 MHz with the proposed Dark Ages Radio Explorer mission in lunar orbit, showing its potential for science return. Author Affiliation: (1)Center for Astrophysics and Space Astronomy, Department of Astrophysics and Planetary Sciences, University of Colorado at Boulder, CO 80309, USA (2)NASA Lunar Science Institute, NASA Ames Research Center, Moffett Field, CA 94035, USA (3)Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA (4)Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, USA Article History: Accepted 2011 September 2. Received 2011 August 31; in original form 2011 July 14 Article note: (★) E-mail: geraint.harker@colorado.edu
    Keywords: Monte Carlo Methods -- Analysis ; Markov Processes -- Analysis ; Space Exploration -- Analysis ; Universities And Colleges -- Analysis ; Nuclear Radiation -- Analysis
    ISSN: 0035-8711
    Source: Cengage Learning, Inc.
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  • 8
    In: Nature, Volume 468, Issue 7325, pp. 796-798 (2010)
    Description: Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (〉100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 〈 z 〈 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of dz 〈 0.06 at the 95% confidence level. Comment: 8 pages, 2 figures, Published in Nature, Volume 468, Issue 7325, pp. 796-798 (2010)
    Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics
    Source: Cornell University
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  • 9
    Description: A new method of absolute calibration of sky noise temperature using a three-position switched spectrometer, measurements of antenna and low noise amplifier impedance with a vector network analyzer, and ancillary measurements of the amplifier noise waves is described. The details of the method and its application to accurate wideband measurements of the spectral index of the sky noise are described and compared with other methods. Comment: 15 pages, 10 figures, published in Radio Science
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics
    Source: Cornell University
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  • 10
    In: Radio Science, December 2012, Vol.47(6), pp.n/a-n/a
    Description: A new method of absolute calibration of sky noise temperature using a three‐position switched spectrometer, measurements of antenna and low noise amplifier impedance with a vector network analyzer, and ancillary measurements of the amplifier noise waves is described and compared with other methods of calibration. An initial test of the method has been made using brief observations from 55 to 110 MHz at West Forks, Maine, to estimate the sky noise spectral index. Estimates are made of the accuracy that might ultimately be achieved with observations to detect or set limits on the red‐shifted 21 cm line at a radio quiet site. It is concluded that an antenna reflection coefficient better than about −20 dB is required to avoid being limited by the accuracy of the antenna reflection coefficient measurements using a vector network analyzer. Absolute calibration of antenna and spectrometer for sky noise measurements
    Keywords: Antenna ; Calibration ; Spectrometer
    ISSN: 0048-6604
    E-ISSN: 1944-799X
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