THE NEED FOR HIGH RESOLUTION IN STUDIES AIMED AT CONSTRUCTING THE 3D MAGNETIC FIELD STRUCTURE OF AGN

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THE NEED FOR HIGH RESOLUTION IN STUDIES AIMED AT
CONSTRUCTING THE 3D MAGNETIC FIELD STRUCTURE OF
AGN JETS Shane OSullivan

• University College Cork, Ireland

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Introduction
2.3 cm
1.3 cm
7 mm
Diagram Wikipedia
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Introduction
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Introduction

• Helical Magnetic Fields
• Mahmud, Gabuzda Many RM gradients
• First detected by Asada et al. 2002
• Same sign gradient ? lt pitch angle

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Introduction

• Helical Magnetic Fields
• Further evidence generation of CP by Faraday
  conversion due to helical B-field
• With RM gradient intrinsic p orientation
  sign of CP
• Gabuzda et al. 2008,
• MNRAS in press, arXiv0711.4572

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Observations
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Analysis

• Different frequencies probe different Faraday
  depths
• Our current obs ideally suited for FR analysis
  long and short intervals reduce np ambiguity
  in obs polarization angles

• Also allow us to construct RM maps on range of
  scales Faraday depths
• Info on RM distribution and sign in core region
  and out along inner jet

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Analysis
Pushkarev 2001
Important to remove if calculating properties in
source rest frame RM ? (1z)2
VLA Faraday rotation observations to remove
integrated (foreground) RM
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RM Results

• Helical Magnetic Fields
• 0954658 RM gradient

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RM Results

• Helical Magnetic Fields
• Transverse profiles p peak offset from I peak
• RM greater on opposite side of p peak
  (Papageorgiou Cawthorne, 2008)

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RM Results
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Evaluation

• 2200420 (BL Lac)
• Simultaneous observations
• Change in sign of core RM in different frequency
  intervals
• LoS B-field changes with distance from base of
  jet

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Evaluation
Intrinsic EVPA orientation

• 2200420
• Intrinsic B-field dominated by toroidal component
• Core PA changes (precesses Stirling et al. 2003,
  ongoing studies by Cawthorne, Marscher et al.)
• Can explain RM sign changes by bend in jet
  surrounded by helical B-field

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Interpretation

• 2200420
• Head-on view (? lt 1/G) in jet rest frame
• ive RM obs for unresolved jet since dominant LoS
  compnt from top half of jet
• Tail-on view (? lt 1/G) -ive RM for same
  helical field

Helix by V. Vitrishchak
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Interpretation

• 2200420
• VLBI core obsd radiation mostly near t
  1 surface, which changes with freq, so different
  freq intervals probing different physical scales
  of the inner jet
• If jet bends on scales less than lowest freq
  observation possible explanation for RM sign
  changes

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RM Results
-

• For jets that do not display bends, the same
  effect can occur for an accelerating/decelerating
  jet

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RM Results
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Summary of Core RM Results
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Summary
Transverse RM gradient
Helical B-field
CP generation
Core RM sign changes
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VSOP 2
VSOP 2
Faraday rotation analysis closer to central
engine with excellent transverse resolution
VSOP 2
Extremely high RMs Higher resolution means
reduction in beam depolarization new core p
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Thank You!
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Data Reduction

• Calibration Imaging done in AIPS
• Mapping done with AIPS task imagr, using robust
  weighting, mixture of natural and uniform
  weighting schemes.
• Very useful for VLBA data because need good
  resolution to image core but also need
  sensitivity to extended jet structure

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IFR

• Internal Faraday Rotation
• Rotation gt 45o without ? in m EXTERNAL

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Attridge
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Attridge

• 3C273 43 - 86 GHz
• Minimum RM 21,000 rad/m2 in observer frame
• Minimum rotation 65o
• Depolarization not consistent with IFR
• Must be EXTERNAL

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RM Variability
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RM Variability

• Short timescale RM variations
• Geometry of jet reflected in RM
• Zavala Taylor Dt 1.3 3 yrs months?
• F rotating medium must be close to source
• Geometry of jet reflected on RM distribution
• ZT map
• Boundary Layer or Sheath