Multi-frequency polarization
structure of the (sub-)pc scale jet
in 3C273 at mm-wavelengths
Tuomas Savolainen
Aalto University Metsähovi Radio Observatory, Finland
Max-Planck-Institut für Radioastronomie, Germany
VLBI-scale Faraday rotation in the jet
of 3C273 at cm-wavelengths
McKinney & Blandford 2009
Zavala & Taylor (2005)
Hovatta et al. (2012)
100 𝑟𝑆
Asada et al. (2002)
2
43-86 GHz EVPA difference
(Attridge et al. 2005)
McKinney & Blandford 2009
• No absolute EVPA calibration at
86 GHz, but 67° change in
Δ𝜒43−86 across the jet at
0.8mas from the core
• ∆RM > 3.2 × 104 rad m−2
• Depolarized core. If external,
𝜎𝑅𝑀 > 5 × 104 rad/m2
100 𝑟𝑆
3
43-86 GHz EVPA difference
(Hada et al. 2016)
McKinney & Blandford 2009
100 𝑟𝑆
No absolute EVPA calibration at 86 GHz.
Δ𝜒 = 50° indicates ∆RM > 2.4 × 104 rad m−2
4
15-86 GHz VLBA polarimetry
of 3C273 in Oct 2010
McKinney & Blandford 2009
15 GHz
24 GHz
100 𝑟𝑆
𝐼𝑝𝑒𝑎𝑘 𝐼𝑏𝑎𝑠𝑒 = 2500
𝐼𝑝𝑒𝑎𝑘 𝐼𝑏𝑎𝑠𝑒 = 1300
5
15-86 GHz VLBA polarimetry
of 3C273 in Oct 2010
McKinney & Blandford 2009
43 GHz
86 GHz
100 𝑟𝑆
86 GHz EVPA calibration using
IRAM 30-m (Agudo et al. 2014)
𝐼𝑝𝑒𝑎𝑘 𝐼𝑏𝑎𝑠𝑒 = 600
𝐼𝑝𝑒𝑎𝑘 𝐼𝑏𝑎𝑠𝑒 = 260
6
Differences in EVPA
between 86 and 43 GHz
McKinney & Blandford 2009
100 𝑟𝑆
7
Differences in EVPA
between 86 and 43 GHz
∆𝐑𝐌 ≳ 𝟐 × 𝟏𝟎𝟒 𝐫𝐚𝐝 𝐦−𝟐
McKinney & Blandford 2009
∆𝝌 = +𝟓°
∆𝝌 = −𝟐𝟎°
𝑹𝑴 ~ 𝟏 × 𝟏𝟎𝟒 𝐫𝐚𝐝 𝐦−𝟐
100 𝑟𝑆
∆𝝌 = −𝟒𝟓°
8
Polarization degree and depolarization
McKinney & Blandford 2009
m = 𝟒 ± 𝟏%
m ≈ 𝟎. 𝟓%
m = 𝟏𝟎 ± 𝟐%
m = 𝟕 ± 𝟏%
100 𝑟𝑆
m ≈ 𝟐𝟎%
86 GHz
43 GHz
Depolarization close to the core. If due to external
Faraday dispersion , 𝜎𝑅𝑀 ≳ 2 × 104 rad/m2
9
Need for higher N-S resolution
Super-resolved
0.15 mas circ. beam
• Transverse polarization structure
within first milliarcsec (2.4 pc /
4000 𝑟𝐺 )
• “Thread” of polarized emission
with EVPA following the bend
inside the jet?
• Need for more N-S resolution
and more sensitivity at 86GHz:
GMVA+ALMA observations last
April (Akiyama et al.)
10
Summary
• Obtained high-quality 15-86 GHz polarimetric
VLBA images of 3C273 – including EVPA
calibration also at 86 GHz
• Confirms the earlier results of RM ≳ 2 ×
104 rad m−2 inside the first milliarcsecond
• Depolarized core at 43 GHz indicating 𝜎𝑅𝑀 ≳
2 × 104 rad/m2
• Calibrated 86 GHz EVPAs seem to align with a
bend inside the first milliarcsecond
11
BACKUP SLIDES
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RM “mapping” at 86-24 GHz
McKinney & Blandford 2009
100 𝑟𝑆
Problems: (very) poor 𝜆2 -coverage, not
enough resolution at 24 GHz, possible
non- 𝜆2 behaviour …
13
Multifrequency VLBA
polarimetry at 15-86 GHz
• Observations on 27 Oct 2010 (part of a longer monitoring
program)
• Obs. freqs. 15, 24, 43 and 86 GHz
• Targets: 3C273, 3C279
• Additional calibrators: 0923+392, 1308+326
• D-term rms: 0.024 (86GHz), 0.010 (43GHz), 0.006
(24GHz), 0.004 (15GHz)
• Absolute EVPA calibration by UMRAO (15GHz, M.Aller),
VLA (24, 43 GHz), IRAM-30 (86 GHz; Agudo et al. 2014)
• 𝜎(EVPA): 5° (15GHz), 5° (24GHz), 5° (43GHz), 7° (86GHz)
14
43-86 GHz spectral index image
McKinney & Blandford 2009
100 𝑟𝑆
15
Differences in EVPA
between 86 and 43 GHz
∆𝐑𝐌 ≳ 𝟐 × 𝟏𝟎𝟒 𝐫𝐚𝐝 𝐦−𝟐
McKinney & Blandford 2009
∆𝝌 = +𝟓°
∆𝝌 = −𝟐𝟎°
𝑹𝑴 ~ 𝟏 × 𝟏𝟎𝟒 𝐫𝐚𝐝 𝐦−𝟐
100 𝑟𝑆
∆𝝌 = −𝟒𝟓°
16
Polarization degree along the jet
McKinney & Blandford 2009
43 GHz
86 GHz
100 𝑟𝑆
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Blank slide
McKinney & Blandford 2009
100 𝑟𝑆
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