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Absorption of -rays
Fabrizio Tavecchio
INAF-Oss. Astron. di Brera, Italy
Absorption of gamma rays
- x1
x2
Absorption of -rays Fabrizio Tavecchio INAF-Oss. Astron. di Brera, - - PowerPoint PPT Presentation
Absorption of -rays Fabrizio Tavecchio INAF-Oss. Astron. di Brera, - - PowerPoint PPT Presentation
Absorption of -rays Fabrizio Tavecchio INAF-Oss. Astron. di Brera, Italy Absorption of gamma rays + -> e+ + e- x 2 In the center of mass the total energy must exceed x 1 2m e c 2 Absorption of gamma rays +
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Hz
Absorption of gamma rays
- x1
x2
+ -> e+ + e-
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Internal opacity: limit on - 1
Observations of gamma rays provide interesting limits on the minimum value
- f the Doppler factor
E=10-100 GeV h=5-50 eV (UV photons)
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Internal opacity: limit on - 1
Observations of gamma rays provide interesting limits on the minimum value
- f the Doppler factor
E=10-100 GeV h=5-50 eV (UV photons)
Without any correction:
(x)= R n(1/x) 1/x ~ (1/x) ~ x increasing with E (x=E/mc2)
where n(1/x) 1/x ~ L (1/x) / R2
(100 GeV)>>1 gamma-rays cannot escape!!
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Taking into account relativistic motion:
1)
1) Intrinsic energy of gamma-ray is lower:
2)
decreasing number density of target photons 2) Density of target soft photons also strongly decreases (lower luminosity, larger radius)
e.g. Ghisellini & Dondi 1996
One finds:
‘ (x)= (x)/4+2
> (x)1/(4+2)
Typically >5
Internal opacity: limit on - 2
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Blazars as cosmic beacons
Blazars illuminate the Universe with gamma rays Gamma rays interact with the IR-O-UV bkg producing pairs
(e.g. Stecker 1966, Nikishov 1966)
Spectral distortions useful to probe the poorly known Extragalactic Background Light (EBL) Pairs re-emit through IC with CMB. Trajectories and fluxes depends on intergalactic magnetic fields
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Cosmic beacons
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Extragalactic background light
EBL measurements
Mazin & Raue 2007
Starlight Dust
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Modeling EBL
Dominguez-Diaz et al. 2010
Starlight
Dust
Energy
100 GeV 1 TeV 10 TeV | | |
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Modeling EBL
Dominguez-Diaz et al. 2010
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The “gamma-ray horizon”
Coppi & Aharonian 1997
Cen A M87 Mkn 501 3C 273
Mean free path =1
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Log E Log F(E)
E
- 2
E
- 2/3
Shock acceleration SSC, large Emin
Constraining EBL with VHE spectra of blazars
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Log E Log F(E)
E
- 2
E
- 2/3
Shock acceleration SSC, large Emin
Constraining EBL with VHE spectra of blazars
Aharonian et al. 2006
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Cosmic beacons
Mankuzhiyil, Persic & FT 2010
Modelled spectra
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Effect of IGMF
Primary emission
Emission cone (BEAMING)
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Effect of IGMF
EBL
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Inverse Compton
- n CMB
Reprocessed emission
Typical energies of reprocessed photons
!"#"!$$""%&'
Effect of IGMF
“cooled “ distribution
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B=0
()&"*&+*,-&..&/"&01..1,2"1."-,23412&/" 513)12"3)&"+*104*6"7&40128"-,2&
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B>0
Effective B-field
The reprocessed flux is diluted within a larger solid angle
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A simplified model for the spectrum
FT et al. 2010
Stationary VHE flux!
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Basic requirements
Hard and powerful TeV spectrum Large distance (high absorption) Low intrinsic GeV flux
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1ES 0229+200: the source of desires
FT et al. 2009
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1ES 0229+200: the source of desires
FT et al. 2009
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B>0!
FT et al. 2010 Neronov & Vovk 2010
Stationary VHE flux!
Dolag et al. 2011
See also: Taylor et al. 2011 Huan et al. 2011
B=10-16-10-15 G
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Adesso .... pappa!
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Intergalactic absorption
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- f the
BL Lac 1101-232 (z=0.186) found that, even assuming the lowest level of the IR background (estimated through galaxy counts), the de-absorbed spectrum is very hard (=1.5).
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Katarzinski et al. 2006 can be obtained assuming a power law electron distribution with a relatively large lower limit min
F ~ 1/3
The absolute limit is: Synchrotron SSC Below the corresponding freq. synchrotron and SSC spectra are very hard!
HESS data deabs. with the best model of Kneiske et al. 2004
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VHE emission of FSRQs
3C 279, z=0.536
Albert at al. 2008
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Constraints from 3C279 Albert at al. 2008
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- ray emission from non-blazar AGNs
Only one non–blazar AGNs is known at VHE band: the radiogalaxy M87
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- ray emission from non-blazar AGNs
Only one non–blazar AGNs is known at VHE band: the radiogalaxy M87
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VHE emission of M87
Light curve Spectrum t var ~ 2 days !
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Emission region?
Large scale jet Stawarz et al. 2003 Knot HST-1 (60 pc proj.) Stawarz et al. 2006 Cheung et al. 2007 Misaligned (20 deg) blazar Georganopoulos et al. 2005 Lenain et al. 2007 FT and GG 2008 BH horizon Neronov & Aharonian 2007 Rieger & Aharonian 2008
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Core?
Acciari et al. 2008
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Ghisellini Tavecchio Chiaberge 2005 Tavecchio & Ghisellini 2008
spine layer
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rel= layerspine(1-layerspine) The spine sees an enhanced Urad coming from the layer Also the layer sees an enhanced Urad coming from the spine
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Misaligned structured blazar jet
FT and GG 2008
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New problems: Ultra-rapid variability
Aharonian et al. 2007 - H.E.S.S. Albert et al. 2007 - MAGIC
Mkn 501 PKS 2155-304
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Observed time: (R0/c)2(1-cos) ~ R0/c ! Rees 1978 for M87
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tvar =200 s
In the standard scenario tvar > rg /c = 1.4 M9 h !
Conclusion:
- nly a small portion of the jet (and/or BH horizon)
is involved in the emission (e.g. Begelman, Fabian & Rees 2008)
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Possible alternative: VHE emission from a fast, transient “needle”
(Ghisellini & Tavecchio 2008) VHE emission dominated by IC from the needle (spine) scattering the radiation of the jet (layer)
A different “flavour” of the spine-layer scenario
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GG & FT 2008 Jet - needle
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The future -1 Fermi (former GLAST) !
First light, 96 hrs of integration
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The future -2 New Cherenkov Telescope Arrays:
CTA, Europe
?
AGIS, USA
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