Journal ArticleDOI
On the Relative Brightness of Coronal Holes at Low Frequencies
TLDR
In this paper, the authors present low-frequency radio observations of coronal holes (CHs) made with the Murchison Widefield Array (MWA) and compare their observations to synthetic images obtained using the software suite FORWARD, in combination with the magnetohydrodynamic algorithm outside a sphere (MAS) model.Abstract:
We present low-frequency (80 – 240 MHz) radio observations of coronal holes (CHs) made with the Murchison Widefield Array (MWA). CHs are expected to be dark structures relative to the background corona across the MWA bandwidth due to their low densities. However, we observe that multiple CHs near disk center transition from being dark structures at higher frequencies to bright structures at lower frequencies (
${\lesssim} \, 145~\mbox{MHz}$
). We compare our observations to synthetic images obtained using the software suite FORWARD, in combination with the magnetohydrodynamic algorithm outside a sphere (MAS) model of the global coronal magnetic field, density, and temperature structure. The synthetic images do not exhibit this transition, and we quantify the discrepancy as a function of frequency. We propose that the dark-to-bright transition results from refraction of radio waves into the low-density CH regions, and we develop a qualitative model based on this idea and the relative optical depths inside and outside a CH as a function of frequency. We show that opacity estimates based on the MAS model are qualitatively consistent with our interpretation, and we conclude that propagation and relative absorption effects are a viable explanation for the dark-to-bright transition of CHs from high to low frequencies.read more
Citations
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Journal ArticleDOI
The Low-Frequency Solar Corona in Circular Polarization
Patrick I. McCauley,Iver H. Cairns,Stephen M. White,Surajit Mondal,Emil Lenc,John Morgan,Divya Oberoi +6 more
TL;DR: In this paper, the authors present spectropolarimetric imaging observations of the solar corona at low frequencies (80, − 240 MHz) using the Murchison Widefield Array (MWA) and introduce an algorithm to mitigate an instrumental artifact by which the total intensity signal contaminates the polarimetric images due to calibration errors.
Journal ArticleDOI
Structure of the solar atmosphere: a radio perspective
TL;DR: In this paper, the authors present a review of the physical processes that determine solar radio emission and link the radio domain with the rest of the electromagnetic spectrum, which is necessary to understand the solar radio emissions.
Journal ArticleDOI
Incoherent Solar Radio Emission
TL;DR: In this article, the authors discuss free-free, gyroresonance and gyrosynchrotron emission mechanisms and their diagnostic potential for the non-flaring solar atmosphere.
Journal Article
Radio Burst and Circular Polarization Studies of the Solar Corona at Low Frequencies
TL;DR: In this paper, low-frequency (80-240 MHz) radio observations of the solar corona are presented using the Murchison Widefield Array (MWA), and several discoveries are reported.
Dissertation
Dark-to-bright Transition of Coronal Holes and Spectropolarimetric Imaging of Type III Solar Radio Bursts Using the MWA.
TL;DR: RahRahman et al. as mentioned in this paper presented low-frequency (80 − 240 MHz) radio observations of coronal holes (CHs) made with the Murchison Widefield Array (MWA) interferometer.
References
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Journal ArticleDOI
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)
James R. Lemen,Alan M. Title,David J. Akin,Paul Boerner,C. Chou,Jerry F. Drake,Dexter W. Duncan,Christopher G. Edwards,Frank M. Friedlaender,Gary F. Heyman,Neal E. Hurlburt,N. Katz,Gary D. Kushner,M. Levay,Russell W. Lindgren,D. Mathur,Edward L. McFeaters,Sarah D. Mitchell,Roger A. Rehse,Carolus J. Schrijver,L. Springer,L. Springer,Robert A. Stern,Theodore D. Tarbell,Jean-Pierre Wuelser,C. Jacob Wolfson,C. Yanari,Jay A. Bookbinder,Peter Cheimets,David Caldwell,Edward E. DeLuca,Richard Gates,Leon Golub,Sang Park,William A. Podgorski,R. I. Bush,Philip H. Scherrer,Mark A. Gummin,Peter L. Smith,Gary Auker,Paul Jerram,Peter J. Pool,Regina Soufli,David L. Windt,Sarah Beardsley,Matthew Clapp,J. Lang,Nicholas R. Waltham +47 more
TL;DR: The Atmospheric Imaging Assembly (AIA) as discussed by the authors provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution.
Book
Radiative processes in astrophysics
TL;DR: Inverse square law for a uniformly bright sphere as discussed by the authors is used to define specific intensity and its moments, which is defined as the specific intensity or brightness of a sphere in terms of specific intensity.
Journal ArticleDOI
The Murchison widefield array: The square kilometre array precursor at low radio frequencies
Steven Tingay,Robert F. Goeke,Judd D. Bowman,David Emrich,Stephen M. Ord,Daniel A. Mitchell,Miguel F. Morales,T. Booler,Brian Crosse,Randall B. Wayth,Colin J. Lonsdale,S. E. Tremblay,D. Pallot,T. Colegate,Andreas Wicenec,Nadia Kudryavtseva,W. Arcus,David G. Barnes,Gianni Bernardi,Frank H. Briggs,S. Burns,John D. Bunton,Roger J. Cappallo,Brian E. Corey,Avinash A. Deshpande,Ludi deSouza,Bryan Gaensler,Lincoln J. Greenhill,Peter J. Hall,Bryna J. Hazelton,David Herne,Jacqueline N. Hewitt,Melanie Johnston-Hollitt,David L. Kaplan,Justin C. Kasper,B. B. Kincaid,R. Koenig,Eric Kratzenberg,Mervyn J. Lynch,Benjamin McKinley,Stephen R. McWhirter,Edward H. Morgan,Divya Oberoi,Joseph Pathikulangara,Thiagaraj Prabu,Ron Remillard,Alan E. E. Rogers,A. Roshi,Joseph E. Salah,Robert J. Sault,N. Udaya-Shankar,F. Schlagenhaufer,K. S. Srivani,Jamie Stevens,Ravi Subrahmanyan,M. Waterson,Rachel L. Webster,Alan R. Whitney,Andrew Williams,Christopher L. Williams,J. S. B. Wyithe +60 more
TL;DR: The Murchison Widefield Array (MWA) as discussed by the authors is one of three Square Kilometre Array Precursor telescopes and is located at the MUR-astronomy Observatory in Western Australia, a location chosen for its extremely low levels of radio frequency interference.
Journal ArticleDOI
Radio Emission from the Sun and Stars
TL;DR: In this paper, the authors present a review of the mechanisms for both steady, quiescent emission and intense, strongly varying outbursts of the sun's radiation, defined as those appearing on classical Hertzsprung-Russell diagrams.
Journal ArticleDOI
The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
Steven Tingay,Robert F. Goeke,Judd D. Bowman,David Emrich,Stephen M. Ord,Daniel A. Mitchell,Miguel F. Morales,Tom Booler,Brian Crosse,D. Pallot,Andreas Wicenec,W. Arcus,David G. Barnes,Gianni Bernardi,Frank H. Briggs,S. Burns,John D. Bunton,Roger J. Cappallo,T. Colegate,Brian E. Corey,Avinash A. Deshpande,L. deSouza,Bryan Gaensler,Lincoln J. Greenhill,J. Hall,Bryna J. Hazelton,David Herne,Jacqueline N. Hewitt,Melanie Johnston-Hollitt,David L. Kaplan,Justin C. Kasper,B. B. Kincaid,R. Koenig,Eric Kratzenberg,Colin J. Lonsdale,Mervyn J. Lynch,Benjamin McKinley,Stephen R. McWhirter,Edward H. Morgan,Divya Oberoi,Joseph Pathikulangara,Thiagaraj Prabu,Ron Remillard,Alan E. E. Rogers,A. Roshi,Joseph E. Salah,Robert J. Sault,N. Udaya-Shankar,F. Schlagenhaufer,K. S. Srivani,Jamie Stevens,Ravi Subrahmanyan,S. E. Tremblay,Randall B. Wayth,M. Waterson,Rachel L. Webster,Alan R. Whitney,Andrew Williams,Christopher L. Williams,J. S. B. Wyithe +59 more
TL;DR: The Murchison Widefield Array (MWA) as mentioned in this paper is one of three Square Kilometre Array Precursor telescopes and is located at the MUR-astronomy Observatory in Western Australia, a location chosen for its extremely low levels of radio frequency interference.
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