Location of the TEVemitting region in PKS 2155304

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Location of the TEV-emitting region in PKS
2155-304

• Geoff Bicknell
• Research School of Astronomy Astrophysics
• Australian National University
• Stefan Wagner
• Landessternwarte
• University of Heidelberg

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Variability of PKS 2155-304
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Where is the emitting region?
If the emitting region is close to the black hole
then conventional values of Doppler factor 10
may be OK
If the emitting region 1016 cm in size then
Doppler factor may be 100
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Absorption of Gamma Rays by pair production

• Jet irradiated by emission from accretion disk
  gt Pair production
• Complicated by fact that radiation from disk can
  be reduced by power in disk wind

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Pair production from photon-photon collisions
Threshold energy
Minimum threshold
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Calculation of pair opacity
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Pair opacity (Gould Schreder, 1967 Donea
Protheroe, 2003)
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Disk spectrum
Kinetic power of Poynting flux dominated jet (GB
Li, 2008 Kuncic GB, 2004)
Shakura-Sunyaev disk temperature
9
Accretion rate
Jet power
Begelman, Fabian Rees (2008)
Estimates from prior models (e.g Aharonian, Sol
et al.)
10
Results
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Turbulent jets (3D Simulations by Toby Potter)
Density
Pressure
Mach 1 turbulent jets illustrate the formation of
shocks and high pressure (high emissivity)
regions in turbulent flow
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2 component models
Increased emission in GeV - TeV range
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Main points

• TeV (and lower energy) photons strongly absorbed
  near accretion disk
• Relative opacity depends on height gt Spectral
  index of moving blob would change when
  propagating away from the black hole
• One way to avoid significant opacity is for the
  disk emission to be strongly suppressed (e.g. by
  diversion of energy into a wind)

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• 2 component models may possibly get around some
  of the problems associated with one-zone models
• Inidcations are that emission in the GLAST energy
  range will be more significant