J/A+A/609/A68 Full-Stokes polarimetry of 5 radio sources (Myserlis+, 2018)
Full-Stokes polarimetry with circularly polarized feeds.
Sources with stable linear and circular polarization in the GHz regime.
Myserlis I., Angelakis E., Kraus A., Liontas C.A., Marchili N., Aller M.F.,
Aller H.D., Karamanavis V., Fuhrmann L., Krichbaum T.P., Zensus J.A.
<Astron. Astrophys. 609, A68 (2018)>
=2018A&A...609A..68M 2018A&A...609A..68M (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, radio ; Polarization ;
Radio continuum ; Radio sources
Keywords: polarization - techniques: polarimetric - galaxies: active -
radio continuum: galaxies - methods: data analysis - galaxies: jets
Abstract:
We present an analysis pipeline that enables the recovery of reliable
information for all four Stokes parameters with high accuracy. Its
novelty relies on the effective treatment of the instrumental effects
even before the computation of the Stokes parameters, contrary to
conventionally used methods such as that based on the Mueller matrix.
For instance, instrumental linear polarization is corrected across the
whole telescope beam and significant Stokes Q and U can be recovered
even when the recorded signals are severely corrupted by instrumental
effects. The accuracy we reach in terms of polarization degree is of
the order of 0.1-0.2%. The polarization angles are determined with an
accuracy of almost 1. The presented methodology was applied to
recover the linear and circular polarization of around 150 active
galactic nuclei, which were monitored between July 2010 and April 2016
with the Effelsberg 100-m telescope at 4.85GHz and 8.35GHz with a
median cadence of 1.2 months. The polarized emission of the Moon was
used to calibrate the polarization angle measurements. Our analysis
showed a small system-induced rotation of about 1deg at both
observing frequencies. Over the examined period, five sources have
significant and stable linear polarization; three sources remain
constantly linearly unpolarized; and a total of 11 sources have stable
circular polarization degree m_c_, four of them with non-zero m_c_. We
also identify eight sources that maintain a stable polarization angle.
All this is provided to the community for future polarization
observations reference. We finally show that our analysis method is
conceptually different from those traditionally used and performs
better than the Mueller matrix method. Although it has been developed
for a system equipped with circularly polarized feeds, it can easily
be generalized to systems with linearly polarized feeds as well.
Description:
In the publication, we present a novel analysis pipeline that enables
the recovery of radio linear and circular polarization with high
accuracy. Its novelty relies on the effective treatment of the
instrumental linear and circular polarization. The accuracy we reach
in terms of polarization degree is of the order of 0.1-0.2 polarization angles are determined with an accuracy of almost 1
degree.
The presented methodology was applied to recover the linear and
circular polarization of around 150 active galactic nuclei, which were
monitored between July 2010 and April 2016 with the Effelsberg 100m
telescope at 4.85GHz and 8.35GHz with a median cadence of 1.2
months.
In order to examine the quality of our circular polarization
calibration, we compared our measurements against contemporaneous data
obtained by the UMRAO monitoring program. The comparison was performed
for five sources with overlapping data sets in the period of
2010.5-2012.3, namely 3C 84, OJ 287, 3C 279, BL Lac and 3C 454.3.
Specifically, we compared all concurrent data points within a maximum
separation of 2 weeks. The corresponding data sets for the time range
embracing the overlapping period are shown in Fig. C.1 of the paper.
Here we provide the circular polarization data used to create this
figure. These data correspond to the UMRAO data set as well as both
circular polarization calibration methods A and B, presented in the
paper.
Objects:
--------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------
03 19 48.16 +41 30 42.1 3C 84 = NGC 1275
08 54 48.87 +20 06 30.6 OJ 287 = QSO J0854+2006
12 56 11.16 -05 47 21.5 3C 279 = QSO B1253-055
22 02 43.29 +42 16 39.9 BL Lac = QSO J2202+4216
22 53 57.74 +16 08 53.5 3C 454.3 = QSO B2251+158
--------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sources.dat 31 5 Observed sources
figc1.dat 44 621 Circular polarization data
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Byte-by-byte Description of file: sources.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Source name
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 19 F5.2 s RAs Right ascension (J2000)
21 A1 --- DE- Declination sign (J2000)
22- 23 I2 deg DEd Declination (J2000)
25- 26 I2 arcmin DEm Declination (J2000)
28- 31 F4.1 arcsec DEs Declination (J2000)
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Byte-by-byte Description of file: figc1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Source name
10- 13 F4.2 GHz Freq Observed frequency
16- 20 A5 --- Dataset Dataset identifier (1)
23- 31 F9.1 d JD Julian date
34- 38 F5.2 41- 44 F4.2 --------------------------------------------------------------------------------
Note (1): The Dataset identifiers are as follows:
umrao = Circular polarization data from the UMRAO monitoring program
mthdA = Circular polarization measurements calibrated using method A
as described in the paper
mthdB = Circular polarization measurements calibrated using method B
as described in the paper
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Acknowledgements:
Ioannis Myserlis, imyserlis(at)mpifr-bonn.mpg.de
This research is based on observations with the 100-m telescope of the
MPIfR (Max-Planck-Institut fur Radioastronomie) at Effelsberg. This
research has made use of data from the University of Michigan Radio
Astronomy Observatory which has been supported by the University of
Michigan and by a series of grants from the National Science
Foundation, most recently AST-0607523.
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(End) Ioannis Myserlis [MPIfR, Germany], Patricia Vannier [CDS] 15-Sep-2017