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  1. Book ; Online: Mitigating the effect of 1/f noise on the detection of the HI intensity mapping power spectrum from single-dish measurements

    Irfan, Melis O. / Li, Yichao / Santos, Mario G. / Bull, Philip / Gu, Junhua / Cunnington, Steven / Grainge, Keith / Wang, Jingying

    2023  

    Abstract: We present and compare several methods to mitigate time-correlated (1/f) noise within the HI intensity mapping component of the MeerKAT Large Area Synoptic Survey (MeerKLASS). By simulating scan strategies, the HI signal, foreground emissions, white and ... ...

    Abstract We present and compare several methods to mitigate time-correlated (1/f) noise within the HI intensity mapping component of the MeerKAT Large Area Synoptic Survey (MeerKLASS). By simulating scan strategies, the HI signal, foreground emissions, white and correlated noise, we assess the ability of various data processing pipelines to recover the power spectrum of HI brightness temperature fluctuations. We use MeerKAT pilot data to assess the level of 1/f noise expected for the MeerKLASS survey and use these measurements to create realistic levels of time-correlated noise for our simulations. We find the time-correlated noise component within the pilot data to be between 10 and 20 times higher than the white noise level at the scale of k = 0.04 Mpc^-1. Having determined that the MeerKAT 1/f noise is partially correlated across all the frequency channels, we employ Singular Value Decomposition (SVD) as a technique to remove both the 1/f noise and Galactic foregrounds but find that over-cleaning results in the removal of HI power at large (angular and radial) scales; a power loss of 40 per cent is seen for a 3-mode SVD clean at the scale of k = 0.04 Mpc^-1. We compare the impact of map-making using weighting by the full noise covariance (i.e. including a 1/f component), as opposed to just a simple unweighted binning, finding that including the time-correlated noise information reduces the excess power added by 1/f noise by up to 30 per cent.

    Comment: 14 pages, 12 figures, accepted by MNRAS. This replacement features updated simulations which now include foreground emissions, telescope slew time and a receiver and elevation-dependant temperature contribution to each receiver which changes over frequency
    Keywords Astrophysics - Cosmology and Nongalactic Astrophysics ; Astrophysics - Instrumentation and Methods for Astrophysics
    Subject code 612
    Publishing date 2023-02-06
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Book ; Online: HI intensity mapping with MeerKAT

    Li, Yichao / Santos, Mario G. / Grainge, Keith / Harper, Stuart / Wang, Jingying

    1/f noise analysis

    2020  

    Abstract: The nature of the time correlated noise component (the 1/f noise) of single dish radio telescopes is critical to the detectability of the HI signal in intensity mapping experiments. In this paper, we present the 1/f noise properties of the MeerKAT ... ...

    Abstract The nature of the time correlated noise component (the 1/f noise) of single dish radio telescopes is critical to the detectability of the HI signal in intensity mapping experiments. In this paper, we present the 1/f noise properties of the MeerKAT receiver system using South Celestial Pole (SCP) tracking data. We estimate both the temporal power spectrum density and the 2D power spectrum density for each of the antennas and polarizations. We apply Singular Value Decomposition (SVD) to the dataset and show that, by removing the strongest components, the 1/f noise can be drastically reduced, indicating that it is highly correlated in frequency. Without SVD mode subtraction, the knee frequency over a $20\,$MHz integration is higher than $0.1\,\rm Hz$; with just $2$~mode subtraction, the knee frequency is reduced to $\sim 3\times 10^{-3}\,{\rm Hz}$, indicating that the system induced 1/f-type variations are well under the thermal noise fluctuations over a few hundred seconds time scales. The 2D power spectrum shows that the 1/f-type variations are restricted to a small region in the time-frequency space, either with long wavelength correlations in frequency or in time. This gives a wide range of cosmological scales where the 21cm signal can be measured without further need to calibrate the gain time fluctuations. Finally, we demonstrate that a simple power spectrum parameterization is sufficient to describe the data and provide fitting parameters for both the 1D and 2D power spectrum.

    Comment: 14 pages, 12 figures
    Keywords Astrophysics - Cosmology and Nongalactic Astrophysics ; Astrophysics - Instrumentation and Methods for Astrophysics
    Subject code 612
    Publishing date 2020-07-03
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Characterization of optical frequency transfer over 154  km of aerial fiber.

    Gozzard, David R / Schediwy, Sascha W / Wallace, Bruce / Gamatham, Romeo / Grainge, Keith

    Optics letters

    2017  Volume 42, Issue 11, Page(s) 2197–2200

    Abstract: We present measurements of the frequency transfer stability and analysis of the noise characteristics of an optical signal propagating over aerial suspended fiber links up to 153.6 km in length. The measured frequency transfer stability over these links ... ...

    Abstract We present measurements of the frequency transfer stability and analysis of the noise characteristics of an optical signal propagating over aerial suspended fiber links up to 153.6 km in length. The measured frequency transfer stability over these links is on the order of 10<sup>-11</sup> at an integration time of 1 s dropping to 10<sup>-12</sup> for integration times longer than 100 s. We show that wind-loading of the cable spans is the dominant source of short-timescale noise on the fiber links. We also report an attempt to stabilize the optical frequency transfer over these aerial links.
    Language English
    Publishing date 2017-06-01
    Publishing country United States
    Document type Journal Article
    ISSN 1539-4794
    ISSN (online) 1539-4794
    DOI 10.1364/OL.42.002197
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Stabilized microwave-frequency transfer using optical phase sensing and actuation.

    Schediwy, Sascha W / Gozzard, David R / Stobie, Simon / Malan, J A / Grainge, Keith

    Optics letters

    2017  Volume 42, Issue 9, Page(s) 1648–1651

    Abstract: We present a stabilized microwave-frequency transfer technique that is based on optical phase sensing and optical phase actuation. This technique shares several attributes with optical-frequency transfer and, therefore, exhibits several advantages over ... ...

    Abstract We present a stabilized microwave-frequency transfer technique that is based on optical phase sensing and optical phase actuation. This technique shares several attributes with optical-frequency transfer and, therefore, exhibits several advantages over other microwave-frequency transfer techniques. We demonstrated the stabilized transfer of an 8000 MHz microwave-frequency signal over a 166 km metropolitan optical fiber network, achieving a fractional frequency stability of 6.8×10<sup>-14</sup>  Hz/Hz at 1 s integration and 5.0×10<sup>-16</sup>  Hz/Hz at 1.6×10<sup>4</sup>  s. This technique is being considered for use on the Square Kilometre Array SKA1-mid radio telescope.
    Language English
    Publishing date 2017-05-01
    Publishing country United States
    Document type Journal Article
    ISSN 1539-4794
    ISSN (online) 1539-4794
    DOI 10.1364/OL.42.001648
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Book ; Online: The Mid-Frequency Square Kilometre Array Phase Synchronisation System

    Schediwy, Sascha / Gozzard, David / Gravestock, Charles / Stobie, Simon / Whitaker, Richard / Malan, Jocias / Boven, Paul / Grainge, Keith

    2018  

    Abstract: This paper describes the technical details and practical implementation of the Mid-Frequency Square Kilometre Array (SKA) phase synchronisation system. Over a four-year period, the system has been tested on metropolitan fibre-optic networks, on long-haul ...

    Abstract This paper describes the technical details and practical implementation of the Mid-Frequency Square Kilometre Array (SKA) phase synchronisation system. Over a four-year period, the system has been tested on metropolitan fibre-optic networks, on long-haul overhead fibre at the South African SKA site, and on existing telescopes in Australia to verify its functional performance. The tests have shown that the system exceed the 1-second SKA coherence loss requirement by a factor 2560, the 60-second coherence loss requirement by a factor of 239, and the 10-minute phase drift requirement by almost five orders-of-magnitude. The paper also reports on tests showing that the system can operate within specification over the all required operating conductions, including maximum fibre link distance, temperature range, temperature gradient, relative humidity, wind speed, seismic resilience, electromagnetic compliance, frequency offset, and other operational requirements.

    Comment: 11 pages, 8 figures. Accepted for publication in PASA. arXiv admin note: text overlap with arXiv:1805.08414
    Keywords Astrophysics - Instrumentation and Methods for Astrophysics
    Subject code 621
    Publishing date 2018-05-25
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  6. Article ; Online: Bright radio emission from an ultraluminous stellar-mass microquasar in M 31.

    Middleton, Matthew J / Miller-Jones, James C A / Markoff, Sera / Fender, Rob / Henze, Martin / Hurley-Walker, Natasha / Scaife, Anna M M / Roberts, Timothy P / Walton, Dominic / Carpenter, John / Macquart, Jean-Pierre / Bower, Geoffrey C / Gurwell, Mark / Pietsch, Wolfgang / Haberl, Frank / Harris, Jonathan / Daniel, Michael / Miah, Junayd / Done, Chris /
    Morgan, John S / Dickinson, Hugh / Charles, Phil / Burwitz, Vadim / Della Valle, Massimo / Freyberg, Michael / Greiner, Jochen / Hernanz, Margarita / Hartmann, Dieter H / Hatzidimitriou, Despina / Riffeser, Arno / Sala, Gloria / Seitz, Stella / Reig, Pablo / Rau, Arne / Orio, Marina / Titterington, David / Grainge, Keith

    Nature

    2013  Volume 493, Issue 7431, Page(s) 187–190

    Abstract: A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1); ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5-20M cicled dot, probably by means of an accretion disk. The X-ray ...

    Abstract A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1); ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5-20M cicled dot, probably by means of an accretion disk. The X-ray and radio emission are coupled in such Galactic sources; the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 10(39) erg s(-1). The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.
    Language English
    Publishing date 2013-01-10
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 120714-3
    ISSN 1476-4687 ; 0028-0836
    ISSN (online) 1476-4687
    ISSN 0028-0836
    DOI 10.1038/nature11697
    Database MEDical Literature Analysis and Retrieval System OnLINE

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