J/ApJ/771/105 MWA Stokes I 189MHz sources (Bernardi+, 2013)
A 189 MHz, 2400 deg2 polarization survey with the Murchison Widefield
Array 32-element prototype.
Bernardi G., Greenhill L.J., Mitchell D.A., Ord S.M., Hazelton B.J.,
Gaensler B.M., de Oliveira-Costa A., Morales M.F., Udaya Shankar N.,
Subrahmanyan R., Wayth R.B., Lenc E., Williams C.L., Arcus W., Arora B.S.,
Barnes D.G., Bowman J.D., Briggs F.H., Bunton J.D., Cappallo R.J.,
Corey B.E., Deshpande A., deSouza L., Emrich D., Goeke R., Herne D.,
Hewitt J.N., Johnston-Hollitt M., Kaplan D., Kasper J.C., Kincaid B.B.,
Koenig R., Kratzenberg E., Lonsdale C.J., Lynch M.J., McWhirter S.R.,
Morgan E., Oberoi D., Pathikulangara J., Prabu T., Remillard R.A.,
Rogers A.E.E., Roshi A., Salah J.E., Sault R.J., Srivani K.S., Stevens J.,
Tingay S.J., Waterson M., Webster R.L., Whitney A.R., Williams A.,
Wyithe J.S.B.
<Astrophys. J., 771, 105 (2013)>
=2013ApJ...771..105B 2013ApJ...771..105B
ADC_Keywords: Interferometry ; Radio continuum
Keywords: diffuse radiation; ISM: magnetic fields; polarization;
radio continuum: general; surveys; techniques: interferometric
Abstract:
We present a Stokes I, Q and U survey at 189MHz with the Murchison
Widefield Array 32 element prototype covering 2400deg2. The survey
has a 15.6' angular resolution and achieves a noise level of
15mJy/beam. We demonstrate a novel interferometric data analysis that
involves calibration of drift scan data, integration through the
co-addition of warped snapshot images, and deconvolution of the
point-spread function through forward modeling. We present a point
source catalog down to a flux limit of 4Jy. We detect polarization
from only one of the sources, PMN J0351-2744, at a level of
1.8%±0.4%, whereas the remaining sources have a polarization
fraction below 2%. Compared to a reported average value of 7% at
1.4GHz, the polarization fraction of compact sources significantly
decreases at low frequencies. We find a wealth of diffuse polarized
emission across a large area of the survey with a maximum peak of
∼13K, primarily with positive rotation measure values smaller than
+10rad/m2. The small values observed indicate that the emission is
likely to have a local origin (closer than a few hundred parsecs).
There is a large sky area at α≥2h30m where the diffuse
polarized emission rms is fainter than 1K. Within this area of low
Galactic polarization we characterize the foreground properties in a
cold sky patch at (α,δ)=(4h,-27.6°) in terms of
three-dimensional power spectra.
Description:
The observations were carried out at 189MHz (central frequency with a
resolution of 40kHz) with the MWA 32 element ("tile", 32T) prototype,
located in the outback of Western Australia at the Murchison Radio
Observatory, and took place on 2010 September 21, for a total of ∼8hr.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 22 137 Catalog of sources brighter than 4Jy at 189MHz
observed at the with the Murchison Widefield Array
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See also:
VIII/84 : A final non-redundant catalogue for 7C 151-MHz survey (Hales+ 2007)
VIII/79 : The VLA Low-frequency Sky Survey at 74MHz (Cohen+ 2007)
VIII/38 : The Parkes-MIT-NRAO 4.85GHz (PMN) Surveys (Griffith+ 1993-1996)
VIII/35 : Radio Sources observed with Culgoora Circular Array (Slee 1995)
VIII/24 : 6C Survey of Radio Sources - V. (Hales+ 1993)
VIII/15 : Parkes Radio Sources Catalogue (PKSCAT90) (Wright+ 1990)
J/MNRAS/426/3295 : Complete 150MHz GMRT source catalogue (Ghosh+, 2012)
J/ApJ/755/47 : Murchison Widefield Array 110-200MHz obs. (Williams+ 2012)
J/ApJ/734/L34 : 145MHz source measurements by PAPER (Jacobs+, 2011)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJ/642/868 : Rotation measures for 223 pulsars (Han+, 2006)
J/ApJS/80/137 : Southern Extragalactic Radio Sources (Jones+, 1992)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Source identifier
13 A1 --- f_Name [*] first measurements in the 100-200MHz band
15- 18 F4.1 Jy Flux [4/47.7] 189MHz flux
20- 22 F3.1 Jy e_Flux [0.3/2.6] Flux uncertainty (1)
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Note (1): The errors are derived from the standard deviation of the distribution
of pixel intensities in a ∼10'x10' area centered on each source after
it was subtracted from the image.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 22-Jan-2015