VIII/107 GLEAM sources ionospheric position shifts (Helmboldt+, 2020)
Ionospheric irregularities observed during the Galactic and Extra-galactic
All-sky MWA (GLEAM) survey.
Helmboldt J.F., Hurley-Walker N.
<Radio Science, 55, e07106 (2020)>
=2020RaSc...5507106H 2020RaSc...5507106H
=2020yCat.8107....0H 2020yCat.8107....0H
ADC_Keywords: Interferometry ; Earth ; Positional data ; Surveys ;
Radio sources ; Galaxy catalogs
Keywords: ionospheric remote sensing - ionospheric disturbances -
radio interferometry
Abstract:
Nearly 200 hours of observing with the Murchison Widefield Array (MWA)
radio telescope during the Galactic and Extra-galactic All-sky MWA
(GLEAM) survey were used to assemble images of ionospheric structure.
These images cover a nearly 50 degree-wide area on the sky at a
cadence of 10 minutes over many 5-7 hours-long observing runs. They
are generated by tracking the apparent motions of ∼200-800 cosmic
radio sources caused by changes in the transverse gradient of the
ionospheric total electron content. Spectral analysis of these images
revealed that the dataset was dominated by three distinct signatures.
The first is consistent with field-aligned structures within the
topside ionosphere/lower plasmasphere previously imaged with the MWA.
The second are structures that are relatively large and aligned nearly
east/west. Regional weather data implies that these are preferentially
detected when there is a noticeable shear within the sub- tropical jet
stream, which passes near the MWA. This suggests that this signature
may be related to gravity waves launched by jet stream shear. The
final signature is consistent with the properties of so-call
electro-buoyancy waves that are known to occur at midlatitudes at
night. Detections of these were more common when regional sporadic-E
was present, supporting a proposed connection between these waves and
polarization electric fields that may arise within sporadic-E. We
discuss the implications for future observations with the Square
Kilometer Array.
Description:
The expected and measured positions from objects from the Molongo
Reference Catalog (MRC) within the Murchison Widefield Array (MWA)
Galactic and Extra-galactic All-sky MWA (GLEAM) survey. The measured
position offsets are dominated by gradients in ionospheric refraction
over the MWA field of view.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
gleamoff.dat 185 447624 Position offsets for GLEAM/MRC objects
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See also:
VIII/16 : Molonglo Reference Catalogue of Radio Sources (Large+ 1991)
J/ApJS/107/19 : MRC/1Jy Radio source survey. I. (McCarthy+ 1996)
VIII/100 : GaLactic and Extragalactic All-sky MWA survey
(Hurley-Walker+, 2016)
VIII/102 : GLEAM II. Galactic plane (Hurley-Walker+, 2019)
VIII/105 : The GLEAM 4-Jy (G4Jy) Sample (White+, 2020)
Byte-by-byte Description of file: gleamoff.dat
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Bytes Format Units Label Explanations
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1- 10 I10 s Time GPS time (seconds since 06-Jan-1980)
11- 20 A10 --- Name Name from the Molongo Reference Catalog,
HHMM-DDdA
21- 28 F8.4 deg RAdeg Right ascension from MRC (J2000.0)
30- 37 F8.4 deg DEdeg Declination from MRC (J2000.0)
39- 48 F10.6 deg RAOdeg Observed right ascension (J2000.0)
51- 59 F9.6 deg e_RAOdeg ?=-1 Error in right ascension
61- 70 F10.6 deg DEOdeg Observed declination (J2000.0)
73- 81 F9.6 deg e_DEOdeg ?=-1 Error in declination
82- 92 F11.6 mJy Flux Peak flux density at 88MHz
95-103 F9.6 mJy e_Flux ?=-1 Error in peak flux density
105-114 F10.6 arcsec A Major axis
115-126 F12.6 arcsec e_A ?=-1 Error in major axis
128-137 F10.6 arcsec B Minor axis
140-148 F9.6 arcsec e_B ?=-1 Error in minor axis
150-159 F10.6 deg PA [] Position angle (clockwise from north)
161-174 F14.6 deg e_PA ?=-1 Error in position angle
178-185 F8.6 mJy RMS Local image RMS
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Acknowledgements:
Joseph Helmboldt, joseph.helmboldt(at)nrl.navy.mil
(End) Joseph Helmboldt [NRL, USA], Patricia Vannier [CDS] 18-Aug-2020