InverseCompton Emission from the Lobes of 3C353

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Inverse-Compton Emission from the Lobes of 3C353

• YERAC 2007
• Bordeaux, France
• Joanna Goodger

Supervisor Team Martin Hardcastle, Judith
Croston, Jim Hough University of Hertfordshire,
Hatfield, UK
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Overview

• Brief introduction to radio galaxies and emission
  mechanisms
• Data
• Results
• Summary
• Future work

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Motivation
NGC 326

• Why Study Radio-loud Active Galaxies?
• Believed all galaxies have black holes at core
• -Why are only some active?
• Origins of cosmic rays
• - Regions of acceleration jets and hotspots in
  active galaxies?
• AGN Feedback is important in cosmological models
• Crucial in understanding galaxy formation and
  evolution
• Sources of gamma rays

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Radio-loud Active Galaxies

• FRI Radio Galaxies
• Low Luminosity
• Bright jets in centre
• Jet decelerated to sub-relativistic speeds by
  interaction with ISM

Core

• FRII Radio Galaxies
• High Luminosity
• Faint Jets with bright Hotspots at the ends
• Jets remain relativistic, travelling at
  supersonic speeds

Core
FRII
FRI
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Emission Mechanism
Inverse-Compton Emission

• Synchrotron Emission

e.g. CMB
Thermal Emission Bremsstrahlung Line Emission
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3C353
1.4 GHz (21cm) from VLA
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Radio Data Reduction
Flux and Phase Calibration, Channel Calibration
(where applicable), Flagging of noise and
artificial signals, Deep Cleaning and Self
Calibration
Clean Data and image
Raw Data
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5 Band Radio Data
VLA Data
330 MHz
614 MHz
1.4 GHz
8.4 GHz
GMRT Data
15 GHz
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XMM X-ray Data

• Two Epochs of XMM data, from all X-ray cameras
  (pnMOS1MOS2)
• Thermal Emission from the merging cluster
• (not shown)
• CMB Inverse-Compton Emission from the lobes

Radio Contours at 1.4 GHz with a Gaussian
Smoothed X-ray image of the Emission in 3C353
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3C353
Hotspots Synchrotron emission in Radio and X-ray
1.4 GHz (21cm) from VLA
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3C353
Diffuse Lobe Emission Radio Synchrotron
Emission inverse-Compton/CMB X-ray Emission
1.4 GHz (21cm) from VLA
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3C353
The Core Radio synchrotron from base of
jet X-ray absorbed component from central
accretion disc X-ray unabsorbed component from
inner jet
1.4 GHz (21cm) from VLA
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3C353
Jet Knots Radio synchrotron Emission X-ray -
currently unknown for 3C353 either iC or
synchrotron
1.4 GHz (21cm) from VLA
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X-ray Emission in Lobes

• Models fitted to the X-ray spectrum
• - Power law
• - Thermal
• - Power-law Thermal
• Best fit models were the Power-law for both the
  East and West lobes, the West lobe including a
  significant core contribution.
• East Lobe c2 39.6 for 34 d.o.f.
• Photon index, G 1.9 0.4 gt a 0.9 0.4
• West Lobe c2 23.1 for 24 d.o.f.
• Photon index, G 1.2 0.6 gt a 0.2 0.6
• X-ray Emission is Non-Thermal in the Lobes
• With spectral indices consistent with iC/CMB

East Lobe
West Lobe
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X-ray Emission in Lobes

• Fitting a Synchrotron Emission Model to the Radio
  Data (?) allows the Synchrotron ( ) and
  Inverse-Compton Emission ( ) to be
  predicted for the X-ray at equipartition. The
  actual X-ray Data is shown by the bowtie (
  )
• Actual magnetic field strength,
• Bobserved 0.44 0.06 nT
• Predicted magnetic field strength,
• Bpredicted 0.89 nT
• Bpredicted 2 Bobserved

West lobe has B consistent with equipartition but
also with a significant departure from
equipartition, Bobserved 0.68 0.2 nT
Electron Dominated
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Lobe Properties

• The Spectral Index, aR varies by 0.08 across the
  lobe in Radio from steep regions (blue) to flat
  regions (red).
• The corresponding X-ray/Radio ratio varies by a
  factor of 4

Spectral Index Map
Electron Density Variation (B Bmeasured
0.39nT) For D(X-ray/Radio) 4 DaR
0.46 For DaR 0.08 D(X-ray/Radio) 1.2
A variation in Electron Density alone cannot
account for the observed changes
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Lobe Properties

• Magnetic Field Strength Variation (ne const.)
• For D(X-ray/Radio) 4 DB 2.5
• As the critical frequency goes as B, the spectral
  index between 330 MHz and 1.4 GHz, aPL in a steep
  region corresponds to the spectral index between
  1.4 GHz and 8.4 GHz, aLX in a flat region.
• We found aPL (steep) 0.7 so aLX (flat) 0.7
• We measure aLX (flat) 1.11

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Lobe Properties

• Single curve is consistent with a homogenous
  distribution of relativistic electrons together
  with varying magnetic field strength across the
  source
• Katz-Stone et al. 1993

3C353 is consistent with this picture but our
data is not good enough to rule out a B variation
alone accounting for the variation across the
lobes
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Cluster Characterisation

• Zw 1718-0108
• Northern Cluster
• kT 3.3 0.3 keV
• Southern Cluster
• kT 4.0 0.5 keV
• Both Isothermal
• Non-violent merger of originally separate
  components

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Pressure Balance

• Internal Pressures of the East and West lobes
  determined using SYNCH
• 3.4 0.6 x 10-13 Pa and 1.9 0.2 x 10-13 Pa
  respectively

Solid lines indicate observed internal pressures
of the lobes (as above) at the observed radial
distance. The dashed lines indicate the position
of the lobes assuming equipartition
Shift corresponds to 3C353 being 220 kpc in front
or behind the plane of the sky
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Summary

• By fitting iC model to the lobes we found the
  East lobe to be electron dominated and the West
  lobe to be consistent with equipartition (within
  large errors)
• The variation in the electron spectrum cannot
  account for the X-ray/radio ratio variation, but
  a change in B is required
• Cluster comprising of two originally separate,
  isothermal components which are merging
  non-violently

J.L. Goodger et al. 2007 MNRAS in Prep.
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The Future

• Collaboration with Kataoka Stwarz
• Chandra observations of 3C353 has better spatial
  resolution (filaments and jet analysis)
• Hotspot analysis
• Cluster-galaxy interaction

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Questions?