J/A+A/619/A88 High cadence polarization monitoring of OJ287 (Myserlis+, 2018)
High cadence, linear, and circular polarization monitoring of OJ 287.
Helical magnetic field in a bent jet.
Myserlis I., Komossa S., Angelakis E., Gomez J.L., Karamanavis V.,
Krichbaum T.P., Bach U., Grupe D.
<Astron. Astrophys. 619, A88 (2018)>
=2018A&A...619A..88M 2018A&A...619A..88M (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; BL Lac objects ; Polarization ;
Radio continuum ; VLBI ; Radio sources ; Millimetric/submm sources
Keywords: magnetic fields - polarization - quasars: supermassive black holes -
BL Lacertae objects: individual: OJ287 - galaxies: active -
galaxies: jets
Abstract:
We present a multifrequency, dense radio monitoring program of the
blazar OJ287 using the 100-m Effelsberg radio telescope. The program
aims to test different binary supermassive black hole (SMBH) scenarios
and studying the physical conditions in the central region of this
bright blazar. Between December 2015 and January 2017 (MJD
57370-57785), the radio electric vector position angle (EVPA) showed a
large clockwise (CW) rotation by about 340° with a mean rate
of -1.04°/day. Based on concurrent polarized Very Long Baseline
Array (VLBA) data, the rotation seems to originate within the jet core
at 43GHz. Optical polarization data show a similar monotonic CW EVPA
rotation of about -1.1°/day, superposed by shorter and faster
rotations of about 7.8°/day, mainly in the CW sense. When
combined, the single dish, VLBI and optical polarization data are
consistent with a polarized emission component propagating on a
helical trajectory within a bent jet. We constrained the helix arc
length (0.26pc) and radius (about 0.04pc) and the projected jet
bending arc length (about 1.9-7.6pc). The helical trajectory covers
only a part of the jet width, possibly its spine. In addition, we
found a stable polarized component with EVPA (-10°) perpendicular
to the large scale jet, suggesting dominance of the poloidal magnetic
field component.
Description:
We used the recently developed, high-precision data analysis
methodology presented in Myserlis et al. (2018A&A...609A..68M 2018A&A...609A..68M,
Cat. J/A+A/609/A68) to recover all four Stokes parameters. The
methodology is aimed on the effective treatment of the instrumental
linear and circular polarization to reach a precision of 0.001-0.002
in fractional polarization and 1° in polarization angle. We
recovered the total flux density of OJ287 at nine bands from 2.64GHz
to 43GHz, the linear polarization parameters at four bands between
2.64GHz and 10.45GHz, and the circular polarization at two bands,
4.85GHz and 8.35GHz. The data were obtained between December 2015 and
January 2017 (MJD 57370-57785) with mean cadence of ten days. The
corresponding light curves are plotted in Fig. 1 of the paper.
In order to constrain the region around the jet core where the long
EVPA rotation happens, we examined concurrent interferometric datasets
obtained by the Very Long Baseline Array (VLBA). We analyzed six data
sets at 15 GHz obtained by the MOJAVE monitoring program (Lister et
al., 2018ApJS..234...12L 2018ApJS..234...12L, Cat. J/ApJS/234/12) from July 20, 2015 to
January 28, 2017 (MJD 57223-57781) and 17 data sets at 43 GHz obtained
by the Boston University VLBA blazar monitoring program from July 2,
2015 to January 14, 2017 (MJD 57205-57767). We first created the
Stokes I, Q and U maps using the corresponding visibility data that we
retrieved from the online archives. In Fig. 5 of the paper we show a
sample polarized map at each frequency. All images are included in the
current dataset. Then, we transformed the data from Jy/beam to Jy.
Finally, we calculated the integrated Stokes I, Q and U within
predefined circular areas around the core position (i.e. the location
of the peak flux) with radii between 0.05 and 2mas in 0.05mas steps.
The results were used to estimate the integrated polarized flux,
polarization degree and EVPA within each circular area. Here we report
the integrated values for the area with the minimum radius which shows
the long EVPA rotation, namely 0.10mas for the 15GHz data and 0.15mas
for the 43GHz data. For the 43GHz data we report also the integrated
values over the largest circular area of 2mas radius which encircles
the whole extend of the source at that frequency. The corresponding
light curves are plotted in Fig. 6 of the paper.
All EVPA measurements are corrected for the n-pi ambiguity effect by
minimizing the variations between consecutive data points after
accounting for their uncertainties.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
08 54 48.87 +20 06 30.6 OJ287 = QSO J0854+2006
-------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig1i.dat 68 284 Stokes I - Effelsberg
fig1ml.dat 66 162 Linear polarization degree - Effelsberg
fig1pa.dat 70 162 Polarization angle - Effelsberg
fig1mc.dat 68 45 Circular polarization degree - Effelsberg
fig6i.dat 67 33 Integrated Stokes I - VLBA
fig6ml.dat 65 19 Integrated linear polarization degree - VLBA
fig6pa.dat 69 18 Integrated polarization angle - VLBA
list.dat 96 69 List of fits files
fits/* . 69 Individual fits files
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See also:
J/ApJS/234/12 : MOJAVE XV. VLBA 15GHz obs. of AGN jets 1996-2016 (Lister+ 2018)
J/A+A/609/A68 : Full-Stokes polarimetry of 5 radio sources (Myserlis+, 2018)
Byte-by-byte Description of file: fig1i.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 37 F5.2 GHz Freq [2.64/43] Observed frequency (2.64, 4.85, 8.35,
10.45, 14.60, 19.00, 23.05, 32.00, 43.00)
40- 52 F13.5 d JD Julian date
55- 60 F6.3 Jy I Stokes I
63- 68 F6.3 Jy e_I 1-sigma uncertainty on I
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig1ml.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 37 F5.2 GHz Freq [2.64/10.45] Observed frequency
(2.64, 4.85, 8.35, 10.45)
40- 52 F13.5 d JD Julian date
55- 59 F5.2 % ml Linear polarization degree
62- 66 F5.2 % e_ml 1-sigma uncertainty on ml
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig1pa.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 37 F5.2 GHz Freq [2.64/10.45] Observed frequency
(2.64, 4.85, 8.35, 10.45)
40- 52 F13.5 d JD Julian date
55- 61 F7.2 deg EVPA Polarisation angle (EVPA)
64- 70 F7.2 deg e_EVPA 1-sigma uncertainty on EVPA
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig1mc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 37 F5.2 GHz Freq [4.85/8.35] Observed frequency (4.85 or 8.35)
40- 52 F13.5 d JD Julian date
55- 60 F6.2 % mc Circular polarization degree
63- 68 F6.2 deg e_mc 1-sigma uncertainty on mc
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig6i.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 34 I2 GHz Freq [15/43] Observed frequency (15 or 43)
37- 40 F4.2 mas Radius Radius of circular area around core
43- 51 F9.1 d JD Julian date
54- 59 F6.3 Jy I Integrated Stokes I within radius
62- 67 F6.3 Jy e_I 1-sigma uncertainty on I
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig6ml.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 34 I2 GHz Freq [15/43] Observed frequency (15 or 43)
37- 40 F4.2 mas Radius Radius of circular area around core
43- 51 F9.1 d JD Julian date
54- 58 F5.2 % ml Integrated polarization degree within radius
61- 65 F5.2 % e_ml 1-sigma uncertainty on ml
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig6pa.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name [OJ287] Source name
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
33- 34 I2 GHz Freq [15/43] Observed frequency (15 or 43)
37- 40 F4.2 mas Radius Radius of circular area around core
43- 51 F9.1 d JD Julian date
54- 60 F7.2 deg EVPA Integrated polarization angle within radius
63- 69 F7.2 deg e_EVPA 1-sigma uncertainty on EVPA
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx [2048] Number of pixels along X-axis
25- 28 I4 --- Ny [2048] Number of pixels along Y-axis
30- 35 F6.3 GHz Freq [15.352/43.115] Observed frequency (15 or 43)
37- 46 A10 --- Obs.Date Observation date
48- 56 F9.1 d JD Julian date
58- 62 I5 Kibyte size Size of FITS file
64- 75 A12 --- FileName Name of FITS file, in subdirectory fits
77- 96 A20 --- Title Title of the file
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Acknowledgements:
This research is based on observations with the 100-m telescope of the
MPIfR (Max-Planck-Institut fuer Radioastronomie) at Effelsberg.
This research has made use of data from the MOJAVE database that is
maintained by the MOJAVE team (Lister et al., 2018,
2018ApJS..234...12L 2018ApJS..234...12L, Cat. J/ApJS/234/12)
This study makes use of 43GHz VLBA data from the VLBA-BU Blazar
Monitoring Program (VLBA-BU-BLAZAR;
http://www.bu.edu/blazars/VLBAproject.html), funded by NASA through
the Fermi Guest Investigator Program. The VLBA is an instrument of the
Long Baseline Observatory. The Long Baseline Observatory is a facility
of the National Science Foundation operated by Associated
Universities, Inc.
Ioannis Myserlis, imyserlis(at)mpifr-bonn.mpg.de
(End) Ioannis Myserlis [MPIfR, Germany], Patricia Vannier [CDS] 22-Oct-2018