A High Energy Centaur

1
A High Energy Centaur

• High-energy particle acceleration at the
  radio-lobe shock of Centaurus A, J. H. Croston
  et.al. arXiv0901.1346, accepted in MNRAS
• Presenter Paul Edmon
• Journal Club
• 2-05-09

2
Outline

• Centaurus A
• Chandra Observations
• Spectral Fitting
• Dynamical Information
• Comparisons and Conclusions

3
Centaurus A

• Distance 3.7 Mpc
• Visual Magnitude 7.8
• Angular Scale 1 arcsec 17.9 pc
• A FRII Radio Galaxy
• One of the closest AGN to us
• Largest Jet Extent (not in picture) 600 kpc
• Possible Source of UHECR
• Auger anisotropy data has CR clustering around
  Cen A
• Scale of 600-kpc lobes consistent with scale
  needed to produce UHECR (in a 1 µG field, E500
  EeV)

Credit ESO/WFI (Optical), ESO/APEX/A.Weiss
et.al. (Sub-millimetre), Chandra/R. Kraft et.al.
(X-Ray)
4
Chandra Observations

• Compiled from 10 separate ACIS observations
• Time 507 ks
• Band 0.4 2.5 keV
• Resolution 2.3 arcsec
• VLA Contours at 1.4 GHz
• Combined archival data from several observing
  different modes
• Resolution 6.1 x 1.9

5
Regions for Spectral Fitting

• Spectra fitted using APEC (Astrophysical Plasma
  Emission Code) with 5 different models
• Model I Thermal Model with free abundance
• Model II Thermal Model with 0.15 Z?
• Model III Thermal Model with 0.5 Z?
• Model IV Single Power Law
• Model V Combination III and IV

6
Region 1 Spectral Fits
7
Table of Spectral Fits
8
Spectral Maps

• X-ray Spectral Index Map
• Red 0.5
• Blue 2.5
• Temperature Map
• Red 4.0 keV
• Yellow 0.7 keV
• Model V
• Has a large thermal component in the inner region
  and a large nonthermal component in the rest of
  the lobe

9
Broadband SED in Region 2

• X-Ray Spectral Index 1.0 (previous spectral
  index of 2.0 quoted in units of
  photons/cm2/s/keV)
• Left a 0.5, ?break 4.4x104, ?max 5x109
• Right a 0.5, ?max 3x108

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Dynamics

• Since Region 3 is Thermally Dominated we can
  extract dynamical information
• np 0.033 cm-3, nISM(beta model) 0.01 cm-3
• P 1.1x10-10 dyne/cm2, PISM 1.1x10-11 dyne/cm2
  
• M 2.8, v 850 km/s
• Using information from Region 3 we will try to
  get information on Region 2
• np 0.004 cm-3, nISM(beta model) 0.001 cm-3
• Assuming that the lobe is isobaric P 1.1x10-10
  dyne/cm2, PISM 1.3x10-12 dyne/cm2
• M 8.4, v 2600 km/s

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More Dynamics

• From Equipartition B 8 µG
• Enthalpy 7x1056 ergs
• Using expansion speed midway along shell
  1.2x1056 ergs
• Assuming constant expansion the age is 2 Myr
• Mean jet power 1043 ergs/s

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Comparisons and Other Facts

• Synchrotron-IC Lifetime for B 8 µG and ?
  3x108 1.1 kyr
• Expected Shell Thickness at 3.6 keV assuming a
  post-shock velocity of 650 km/s 1 pc
• Expected Shell Thickness at 0.4 keV 3 pc
• Hillas Criterion Maximum Energy 2 EeV

Credit Z. Levay
13
TeV Emission

• Left1µG, Right7µG

14
Conclusions

• The forward shock of the inner lobe of Cen A is
  producing non-thermal synchrotron emission
• Given a microGauss field strength this implies
  particle acceleration up to at least TeV
  energies, analogous to SN 1006 and other
  non-thermal X-ray emitting SNRs
• The shock in Cen A has analogous characteristics
  to the forward shock of SN 1006
• TeV Gamma Ray Emission is predicted to be seen at
  this source.

15
By Analogy
Credit HESS Collaboration