J/ApJ/825/59 LMC and Cen A 1.3-10GHz polarization behavior (Anderson+, 2016)
A study of broadband Faraday rotation and polarization behavior over 1.3-10GHz
in 36 discrete radio sources.
Anderson C.S., Gaensler B.M., Feain I.J.
<Astrophys. J., 825, 59-59 (2016)>
=2016ApJ...825...59A 2016ApJ...825...59A (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Polarization ; Magellanic Clouds
Keywords: galaxies: active; galaxies: jets; galaxies: magnetic fields;
polarization; Sun: magnetic fields; techniques: polarimetric
Abstract:
We present a broadband polarization analysis of 36 discrete polarized
radio sources over a very broad, densely sampled frequency band. Our
sample was selected on the basis of polarization behavior apparent in
narrowband archival data at 1.4GHz: half the sample shows complicated
frequency-dependent polarization behavior (i.e., Faraday complexity)
at these frequencies, while half shows comparatively simple behavior
(i.e., they appear Faraday simple). We re-observed the sample using
the Australia Telescope Compact Array in full polarization, with 6GHz
of densely sampled frequency coverage spanning 1.3-10GHz. We have
devised a general polarization modeling technique that allows us to
identify multiple polarized emission components in a source, and to
characterize their properties. We detect Faraday complex behavior in
almost every source in our sample. Several sources exhibit
particularly remarkable polarization behavior. By comparing our new
and archival data, we have identified temporal variability in the
broadband integrated polarization spectra of some sources. In a number
of cases, the characteristics of the polarized emission components,
including the range of Faraday depths over which they emit, their
temporal variability, spectral index, and the linear extent of the
source, allow us to argue that the spectropolarimetric data encode
information about the magneto-ionic environment of active galactic
nuclei themselves. Furthermore, the data place direct constraints on
the geometry and magneto-ionic structure of this material. We discuss
the consequences of restricted frequency bands on the detection and
interpretation of polarization structures, and the implications for
upcoming spectropolarimetric surveys.
Description:
The targets for our study were selected from among two archival
polarization data sets, which were observed and processed by several
independent groups. i.e. LMC observations spanning from 1994 Oct to
1996 Jan in 1.328-1.432GHz band; Cen A observations spanning from 2006
Dec to 2008 Feb in 1.296-1.480GHz band.
We observed the 40 sample sources using the Australia Telescope
Compact Array (ATCA) over 1.1-3.1GHz (16cm), 4.5-6.5GHz (6cm), and
8.0-10.0GHz (3cm) in full polarization with a nominal 1MHz channel
resolution between 2012 Feb 10-12 and 2012 Aug 17-19.
We imaged each source in Stokes I, Q, and U at 20MHz intervals through
the 16 and 6cm bands, and at a substantially coarser resolution of
200MHz in the 3cm band. See sections 2 and 3 for further explanations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 94 36 Selected observational properties of
our sample sources
table6.dat 95 4748 The spectropolarimetric data
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See also:
J/AJ/149/60 : Modeling Faraday structures. I. 1100-1400 MHz (Sun+, 2015)
J/MNRAS/436/2915 : Polarization of bright AT20G sources (Massardi+, 2013)
J/MNRAS/434/956 : AT20G high-angular-resolution catalogue (Chhetri+, 2013)
J/AJ/144/105 : MOJAVE. VIII. Faraday rotation in AGN jets. (Hovatta+, 2012)
J/ApJ/759/25 : Rotation measures at 1.4GHz toward the LMC (Mao+, 2012)
J/MNRAS/402/2403 : Australia Telescope 20GHz Survey (AT20G) (Murphy+, 2010)
J/ApJ/707/114 : Faraday rotation in Cen A (Feain, 2009)
J/ApJS/45/97 : Extragal. Radio Sources Faraday Rot. (Simard-Normandin+ 1981)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID Source identifier
12- 13 I2 h RAh [4/13] Hour of Right Ascension (J2000)
15- 16 I2 min RAm Minute of Right Ascension (J2000)
18- 22 F5.2 s RAs Second of Right Ascension (J2000)
24 A1 --- DE- [-] Sign of the Declination (J2000)
25- 26 I2 deg DEd [38/74] Degree of Declination (J2000)
28- 29 I2 arcmin DEm Arcminute of Declination (J2000)
31- 35 F5.2 arcsec DEs Arcsecond of Declination (J2000)
37- 44 A8 cm Band Self calibrated band(s)
46- 47 I2 arcsec Size [2/90]? Maximum angular size (1)
49- 51 A3 --- Res Resolved over 1.3-10GHz (2)
53- 58 F6.4 Jy I1.4 [0.007/2.2] Stokes I model value at 1.4GHz
60- 65 F6.4 Jy e_I1.4 [0.0002/0.004] Uncertainty in I1.4
67- 67 I1 --- Imod [1/7] Polynomial degree of I1.4
69- 74 F6.3 --- SpInd [-2.3/0.4] Mean spectral index over
the 1.3-10GHz band
76- 80 F5.3 --- e_SpInd [0.002/0.2] Uncertainty in SpInd
82- 91 A10 --- Vis AT20G High angular resolution catalog
visibility ratio(s) (3)
93- 94 I2 --- Fig ? Figure number for this resolved source;
column added by CDS (4)
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Note (1): The maximum angular size was determined from images at 1.4GHz for
extended sources, and from images at the highest frequency at which
the source remained visible in cases where the source resolved into
multiple separated sub-components towards higher frequencies.
Note (2): A "u" indicates that a source is unresolved over 1.3-10GHz, by which
we mean its peak-to-total flux density ratio is at least 0.95 over
the full range. An "r" indicates that a source is resolved at all
frequencies between 1.3 & 10GHz (i.e. a peak-to-total flux density
ratio of <0.95), while a number indicates the frequency in GHz
above which the source becomes resolved. These designations apply to
observations conducted with the ATCA array configurations listed in
column 4 of Table 1 and imaged using robust =0 weighting.
Note (3): Uncertainties are all ±0.03.
Note (4): In Figures 46-63, images of our resolved sample sources are provided
at both the low and high frequency ends of each CABB band.
See Appendix A.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID Source identifier
12- 19 F8.6 GHz nu [1.27/9.91] Frequency
21- 29 F9.6 Jy I [-0.0017/2.2] Stokes I data
31- 38 F8.6 Jy e_I [0.00015/0.015] Uncertainty in I
40- 48 F9.6 Jy Q [-0.035/0.043] Stokes Q data
50- 57 F8.6 Jy e_Q [0/0.007] Uncertainty in Q
59- 67 F9.6 Jy U [-0.042/0.025] Stokes U data
69- 76 F8.6 Jy e_U [0.0001/0.004] Uncertainty in U
78- 86 F9.6 Jy V [-0.02/0.02] Stokes V data
88- 95 F8.6 Jy e_V [0.0001/0.005] Uncertainty in V
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Aug-2016