Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array

Shyeh Tjing Loi, Tara Murphy, Martin E. Bell, David L. Kaplan, Emil Lenc, André R. Offringa, Natasha Hurley-Walker, G. Bernardi, Judd Bowman, F. Briggs, R. J. Cappallo, B. E. Corey, A. A. Deshpande, D. Emrich, B. M. Gaensler, R. Goeke, L. J. Greenhill, B. J. Hazelton, M. Johnston-Hollitt, J. C. KasperE. Kratzenberg, C. J. Lonsdale, M. J. Lynch, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, D. Oberoi, S. M. Ord, T. Prabu, A. E E Rogers, A. Roshi, N. Udaya Shankar, K. S. Srivani, R. Subrahmanyan, S. J. Tingay, M. Waterson, R. B. Wayth, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Refraction and diffraction of incoming radio waves by the ionosphere induce time variability in the angular positions, peak amplitudes and shapes of radio sources, potentially complicating the automated cross-matching and identification of transient and variable radio sources. In this work, we empirically assess the effects of the ionosphere on data taken by the Murchison Widefield Array (MWA) radio telescope. We directly examine 51 h of data observed over 10 nights under quiet geomagnetic conditions (global storm index Kp < 2), analysing the behaviour of short-time-scale angular position and peak flux density variations of around ten thousand unresolved sources. We find that while much of the variation in angular position can be attributed to ionospheric refraction, the characteristic displacements (10-20 arcsec) at 154 MHz are small enough that search radii of 1-2 arcmin should be sufficient for crossmatching under typical conditions. By examining bulk trends in amplitude variability, we place upper limits on the modulation index associated with ionospheric scintillation of 1-3 per cent for the various nights. For sources fainter than ~1 Jy, this variation is below the image noise at typical MWA sensitivities. Our results demonstrate that the ionosphere is not a significant impediment to the goals of time-domain science with the MWA at 154 MHz.

Original languageEnglish (US)
Pages (from-to)2731-2746
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume453
Issue number3
DOIs
StatePublished - 2015

Keywords

  • Atmospheric effects
  • Instrumentation: interferometers
  • Radio continuum: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Loi, S. T., Murphy, T., Bell, M. E., Kaplan, D. L., Lenc, E., Offringa, A. R., Hurley-Walker, N., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R. J., Corey, B. E., Deshpande, A. A., Emrich, D., Gaensler, B. M., Goeke, R., Greenhill, L. J., Hazelton, B. J., Johnston-Hollitt, M., ... Williams, C. L. (2015). Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array. Monthly Notices of the Royal Astronomical Society, 453(3), 2731-2746. https://doi.org/10.1093/mnras/stv1808