J/A+A/623/A111 3C273 polarization over ALMA 1.3mm band (Hovatta+, 2019)
Magnetic field at a jet base: extreme Faraday rotation in 3C273
revealed by ALMA.
Hovatta T., O'Sullivan S., Marti-Vidal I., Savolainen T., Tchekhovskoy A.
<Astron. Astrophys. 623, A111 (2019)>
=2019A&A...623A.111H 2019A&A...623A.111H (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Polarization
Keywords: polarization - quasars: individual: 3C273 - galaxies: jets -
radio continuum: galaxies
Abstract:
We studied the polarization behavior of the quasar 3C 273 over the 1mm
wavelength band at ALMA with a total bandwidth of 7.5GHz across
223-243GHz at 0.8" resolution, corresponding to 2.1kpc at the
distance of 3C 273. With these observations we were able to probe the
optically thin polarized emission close to the jet base, and constrain
the magnetic field structure.
We computed the Faraday rotation measure using simple linear fitting
and Faraday rotation measure synthesis. In addition, we modeled the
broadband behavior of the fractional Stokes Q and U parameters
(qu-fitting). The systematic uncertainties in the polarization
observations at ALMA were assessed through Monte Carlo simulations.
We find the unresolved core of 3C 273 to be 1.8% linearly polarized.
We detect a very high rotation measure (RM) of
(5.0±0.3)x105rad/m2 over the 1 mm band when assuming a single
polarized component and an external RM screen. This results in a
rotation of >40° of the intrinsic electric vector position angle,
which is significantly higher than typically assumed for millimeter
wavelengths. The polarization fraction increases as a function of
wavelength, which according to our qu-fitting could be due to multiple
polarized components of different Faraday depth within our beam or to
internal Faraday rotation. With our limited wavelength coverage we
cannot distinguish between the cases, and additional multifrequency
and high angular resolution observations are needed to determine the
location and structure of the magnetic field of the Faraday active
region. Comparing our RM estimate with values obtained at lower
frequencies, the RM increases as a function of observing frequency,
following a power law with an index of 2.0±0.2, consistent with a
sheath surrounding a conically expanding jet. We also detect ∼0.2%
circular polarization, although further observations are needed to
confirm this result.
Description:
Stokes parameters and derived polarization fraction and electric
vector position angle of 3C273 for each 31.5MHz wide channel over the
ALMA 1.3mm band. Stokes I, Q, U, V, fractional polarization and
electric vector position angle, and their corresponding uncertainties
are given.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
12 29 06.70 +02 03 08.7 3C273 = QSO J1229+0203
----------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 78 216 Values for each channel for 3C273
--------------------------------------------------------------------------------
See also:
J/MNRAS/392/1181 : BV(RI)c photometry of 3C 273 (Dai+, 2009)
J/ApJS/213/26 : Optical light curves of PHL1811 and 3C273 (Fan+, 2014)
J/A+A/576/A122 : 3C 273 high energy spectrum (Esposito+, 2015)
J/ApJS/229/21 : VRI monitoring of the QSO 3C 273 in 2005-2016 (Xiong+, 2017)
J/A+A/601/A35 : High-fidelity VLA imaging of 3C273 (Perley+, 2017)
J/A+A/604/A111 : 22GHz image of 3C 273 (Bruni+, 2017)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 GHz Freq Center frequency of the channel
8- 12 F5.3 Jy I Stokes I flux density
14- 18 F5.3 Jy e_I 1-sigma uncertainty of Stokes I
20- 25 F6.3 Jy Q Stokes Q flux density
27- 31 F5.3 Jy e_Q 1-sigma uncertainty of Stokes Q
33- 38 F6.3 Jy U Stokes U flux density
40- 44 F5.3 Jy e_U 1-sigma uncertainty of Stokes U
46- 50 F5.3 Jy V Stokes V flux density
52- 56 F5.3 Jy e_V 1-sigma uncertainty of Stokes V
58- 61 F4.2 % Pfrac Polarization fraction
63- 66 F4.2 % e_Pfrac 1-sigma uncertainty of p fraction
68- 73 F6.2 deg EVPA Electric vector position angle
75- 78 F4.2 deg e_EVPA 1-sigma uncertainty of EVPA
--------------------------------------------------------------------------------
Acknowledgements:
Talvikki Hovatta, talvikki.hovatta(at)utu.fi
(End) Talvikki Hovatta [Univ. Turku, Finland] Patricia Vannier [CDS] 05-Feb-2019