J/AJ/144/105 MOJAVE. VIII. Faraday rotation in AGN jets. (Hovatta+, 2012)
MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments.
VIII. Faraday rotation in parsec-scale AGN jets.
Hovatta T., Lister M.L., Aller M.F., Aller H.D., Homan D.C., Kovalev Yu.Y.,
Pushkarev A.B., Savolainen T.
<Astron. J., 144, 105 (2012)>
=2012AJ....144..105H 2012AJ....144..105H
ADC_Keywords: Active gal. nuclei ; BL Lac objects ; QSOs ; Polarization ;
Radio continuum ; Redshifts
Keywords: BL Lacertae objects: general - galaxies: active - galaxies: jets -
polarization - quasars: general - radio continuum: galaxies
Abstract:
We report observations of Faraday rotation measures for a sample of
191 extragalactic radio jets observed within the MOJAVE program.
Multifrequency Very Long Baseline Array observations were carried out
over 12 epochs in 2006 at four frequencies between 8 and 15GHz. We
detect parsec-scale Faraday rotation measures in 149 sources and find
the quasars to have larger rotation measures on average than BL Lac
objects. The median core rotation measures are significantly higher
than in the jet components. This is especially true for quasars where
we detect a significant negative correlation between the magnitude of
the rotation measure and the de-projected distance from the core. We
perform detailed simulations of the observational errors of total
intensity, polarization, and Faraday rotation, and concentrate on the
errors of transverse Faraday rotation measure gradients in unresolved
jets. Our simulations show that the finite image restoring beam size
has a significant effect on the observed rotation measure gradients,
and spurious gradients can occur due to noise in the data if the jet
is less than two beams wide in polarization. We detect significant
transverse rotation measure gradients in four sources (0923+392,
1226+023, 2230+114, and 2251+158). In 1226+023 the rotation measure is
for the first time seen to change sign from positive to negative over
the transverse cuts, which supports the presence of a helical magnetic
field in the jet. In this source we also detect variations in the jet
rotation measure over a timescale of three months, which are difficult
to explain with external Faraday screens and suggest internal Faraday
rotation. By comparing fractional polarization changes in jet
components between the four frequency bands to depolarization models,
we find that an external purely random Faraday screen viewed through
only a few lines of sight can explain most of our polarization
observations, but in some sources, such as 1226+023 and 2251+158,
internal Faraday rotation is needed.
Description:
Our sample consists of 191 AGNs observed within the MOJAVE Very Long
Baseline Array (VLBA) survey (Lister et al., 2009, cat. J/AJ/137/3718,
Paper V). It includes 134 sources of the complete flux density-limited
MOJAVE-1 sample. The rest of the sources belong to the MOJAVE-2 sample
(http://www.physics.purdue.edu/astro/MOJAVE/allsources.html), which
includes sources from the 2cm survey (Kellermann et al. 2004, cat.
J/ApJ/609/539), gamma-ray blazars, and other sources with unusual jet
properties.
The sources were observed with VLBA in 2006 over 12 epochs with about
monthly separation, each epoch containing 18 sources (except for epoch
2006 February 12, which included only 14 sources and epoch 2006 April
28, which included 17 sources). The observations were made in dual
polarization mode using frequencies centered at 8.104, 8.424 (X band),
12.119, and 15.369GHz (U band).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 83 211 Sources and their rotation measure properties
table3.dat 47 428 Model-fit components at 15.3GHz and their RM values
--------------------------------------------------------------------------------
See also:
VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron+ 2010)
J/A+A/545/A113 : MOJAVE IX. Core shift effects (Pushkarev+, 2012)
J/ApJ/722/L7 : Fermi/LAT detected MOJAVE AGNs (Pushkarev+, 2010)
J/ApJ/710/764 : Extended radio emission in MOJAVE blazars (Kharb+, 2010)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJ/706/1253 : MOJAVE VII. Blazar jet acceleration (Homan+, 2009)
J/AJ/138/1874 : MOJAVE. VI. Kinematic analysis of blazar jets (Lister+, 2009)
J/AJ/137/3718 : 15GHz monitoring of AGN jets with VLBA (Lister+, 2009)
J/ApJS/171/376 : MOJAVE. III. VLA 1.4GHz images (Cooper+, 2007)
J/AJ/131/1262 : AGN jets circular polarization images at 15GHz (Homan+, 2006)
J/AJ/130/1389 : Linear polarization of AGN jets at 15GHz (Lister+, 2005)
J/ApJ/609/539 : Kinematics of parsec-scale radio jets (Kellermann+, 2004)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Source IAU name (B1950.0)
10- 25 A16 --- OName Other name
27- 34 F8.6 --- z ? Redshift
36 A1 --- O [QBGU] Optical classification (1)
38- 41 F4.1 c beta ? Apparent speed in units of the speed of
light β=v/c (2)
43- 52 A10 "Y:M:D" Obs.date Date of rotation measure observation
54- 59 F6.1 rad/m2 GRM Galactic rotation measure correction (from
Taylor et al. 2009, cat. J/ApJ/702/1230)
61- 67 F7.1 rad/m2 mRM ? Median rotation measure over source
69- 75 F7.1 rad/m2 mRMc ? Median rotation measure over core area
77- 83 F7.1 rad/m2 mRMj ? Median rotation measure over jet
--------------------------------------------------------------------------------
Note (1): Optical class as follows:
Q = quasar;
B = BL Lac object;
G = active galaxy;
U = unidentified.
Note (2): Used in viewing angle calculation of Figure 4 in this paper.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Source IAU name (B1950.0)
10- 11 I2 --- m_Name [0/26] Component identification
(0=core component)
13- 22 A10 "Y:M:D" Date Date of rotation measure observation
24- 28 F5.2 mas r Component distance from the phase center
of the map
30- 35 F6.1 deg PA [-180/180] Component position angle from
the phase center of the map
37- 41 I5 rad/m2 RM Component rotation measure
43- 45 I3 rad/m2 e_RM Uncertainty in RM
47 A1 --- I [Y] Indicates whether a jet component is
isolated (see Section 3.3 for more details)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Lister et al. Paper I. 2005AJ....130.1389L 2005AJ....130.1389L Cat. J/AJ/130/1389
Homan et al. Paper II. 2006AJ....131.1262H 2006AJ....131.1262H Cat. J/AJ/131/1262
Cooper et al. Paper III. 2007ApJS..171..376C 2007ApJS..171..376C Cat. J/ApJS/171/376
Cara et al. Paper IV. 2008ApJ...674..111C 2008ApJ...674..111C
Lister et al. Paper V. 2009AJ....137.3718L 2009AJ....137.3718L Cat. J/AJ/137/3718
Lister et al. Paper VI. 2009AJ....138.1874L 2009AJ....138.1874L Cat. J/AJ/138/1874
Homan et al. Paper VII. 2009ApJ...706.1253H 2009ApJ...706.1253H Cat. J/ApJ/706/1253
Pushkarev et al. Paper IX. 2012A&A...545A.113P 2012A&A...545A.113P Cat. J/A+A/545/A113
Lister et al. Paper X. 2013AJ....146..120L 2013AJ....146..120L Cat. J/AJ/146/120
Hovatta et al. Paper XI. 2014AJ....147..143H 2014AJ....147..143H Cat. J/AJ/147/143
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Lister et al. Paper XIII. 2016AJ....152...12L 2016AJ....152...12L Cat. J/AJ/152/12
Pushkarev et al. Paper XIV. 2017MNRAS.468.4992P 2017MNRAS.468.4992P Cat. J/MNRAS/468/4992
Lister et al. Paper XV. 2018ApJS..234...12L 2018ApJS..234...12L Cat. J/ApJS/234/12
Hodge et al. Paper XVI. 2018ApJ...862..151H 2018ApJ...862..151H Cat. J/ApJ/862/151
Lister et al. Paper XVII. 2019ApJ...874...43L 2019ApJ...874...43L Cat. J/ApJ/874/43
Lister et al. Paper XVIII. 2021ApJ...923...30L 2021ApJ...923...30L Cat. J/ApJ/923/30
Homan et al. Paper XIX. 2021ApJ...923...67H 2021ApJ...923...67H Cat. J/ApJ/923/67
Pushkarev et al. Paper XX. 2023MNRAS.520.6053P 2023MNRAS.520.6053P
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 24-Oct-2013