Diapositiva 1

1
Inverse Compton Hard X-rays from Galaxy
Clusters
Gianfranco Brunetti
INAF-Istituto di Radioastronomia, Bologna,
Italy Rossella Cassano Universita di Bologna
INAF-IRA Giancarlo Setti Universita di
Bologna INAF-IRA
2
The RE-Acceleration Model (Brunetti et al. 2001,
Petrosian 2001, al.)
IC
MF Amplification
Turbulence
Synchrotron
3
Theoretically
Galaxy Clusters are Lab for stochastic particle
acceleration (e.g. Brunetti Lazarian
2007) Suitable combination of Beta of plasma
(large) Turbulent media Long ion mean free path
(collisionless) Large-scale magnetised systems
Long time-scales
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Diffuse Radio Emission in situ electron
acceleration
Radio Halos are rare (Hwang 2004) Radio Halos
are always found in merging clusters (Buote 2001
Feretti 2004,05) Radio Halos have complex
spectra (spectral steepening, patchy spectral
index) (Brunetti 2002,04 Petrosian 2002 Feretti
et al. 2004,05 Orru et al. 2007) Radio Halos
are very extended (Govoni et al 2001 Brunetti
2002,04 Pfrommer Ensslin 2004 Marchegiani et
al. 2007)
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Diffuse Radio Emission origin of emitting
electrons
In the RE-Acceleration Scenario RH ( HXR) should
be Transient
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Diffuse Radio Emission origin of emitting
electrons
In the RE-Acceleration Scenario RH ( HXR)
should be Transient
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Diffuse Radio Emission origin of emitting
electrons
In the RE-Acceleration Scenario RH ( HXR)
should be Transient
8
Diffuse Radio Emission origin of emitting
electrons
GMRT (T.Venturi et al.2007GB et al.)
Sample of 50 massive GC at z 0.2-0.4 (REFLEX
eBCS) Similar z Similar masses/temperature Simila
r X-ray luminosities
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Diffuse Radio Emission origin of emitting
electrons
GMRT (T.Venturi et al.2007GB et al.)
Radio loud
Radio quiet
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IC HXR from the RE-Acceleration Model
For suitable (but viable) conditions the IC from
re-accelerated electrons/positrons can match the
observed HXRs There is a big degeneracy in
the synchrotron expectations (synchrotron
degeneracy)
Brunetti Blasi 2005
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Cassano Brunetti 2005 Cassano et al. 2006
HXR Calculations
vi
M1
M2
Merging Trees
Efm?fm vi2
Turbulent injection
Particle Acceleration
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Cassano Brunetti 2005 Cassano et al. 2006
HXR Calculations
B?Mb
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B?Mb
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Consequence HXR Results
Luminosity Functions
Number Counts
z0.05 z0.25 z0.45
HXR Tails (from re-accelerated electrons in Mpc
regions) are produced in massive clusters, Mvir
gt1015Mo
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Consequence HXR Results
Luminosity Functions
Number Counts
z0.05 z0.25 z0.45
HXR Tails (from re-accelerated electrons in Mpc
regions) are produced in massive clusters, Mvir
gt1015Mo
BeppoSAX
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Consequence HXR Results
Luminosity Functions
Simbol-X
Number Counts
z0.05 z0.25 z0.45
HXR Tails (from re-accelerated electrons in Mpc
regions) are produced in massive clusters, Mvir
gt1015Mo
BeppoSAX
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Consequence HXR Results
Redshift distribution
The bulk of HXR tails from re-accelerated particl
es is expected at z0-0.2 for typical Simbol X
surveys Shallow surveys are expected to catch
only local HXR tails
F gt10-13 cgs
F gt510-13 cgs
F gt10-12 cgs
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Conclusions
Presently known RH are probably complex and
transient (re-acceleration scenario..), they are
probably just the tip of the iceberg . Present
Modelling of particle re-acceleration may provide
first expectations for IC HXR Tails emitted from
the re-accelerated electrons/positrons Catching
IC signals from Galaxy Clusters is important
to break the synchrotron degeneracy
(Particle-Field) In case the HXR Tails
discovered by BeppoSAX RXTE are all real
SIMBOL-X should catch HXR Tails from
10-100 massive Galaxy Clusters at z0.0-0.2
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Conclusions
Presently known RH are probably complex and
transient (re-acceleration scenario..), they are
probably just the tip of the iceberg . Present
Modelling of particle re-acceleration may provide
first expectations for IC HXR Tails emitted from
the re-accelerated electrons/positrons Catching
IC signals from Galaxy Clusters is important
to break the synchrotron degeneracy
(Particle-Field) In case the HXR Tails
discovered by BeppoSAX RXTE are all real
SIMBOL-X should catch HXR Tails from
10-100 massive Galaxy Clusters at z0-0.2
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(No Transcript)
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Diffuse Radio Emission origin of emitting
electrons
MF is ubiquitous in GC CRp secondaries are
ubiquitous
Miniati et al. 2001
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Kinetic Fully Non-linear Wave--Particle
Coupling (Brunetti al. 2004 Brunetti Blasi
2005 Brunetti Lazarian 2007)
Waves spectra
Electron spectra
Ee 0.001 Eth Ep 0.005 Eth s3.2
Proton spectra
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Cassano Brunetti 2005 Cassano et al. 2006
HXR Calculations
Simplified Plasma Physics Simplified
Cosmological formalism (E-PS)
Merging Trees
Turbulent injection
Particle Acceleration
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CR in Galaxy Clusters
CR Confinment in Galaxy Clusters (e.g., Voelk et
al. 1996, Berezinsky et al. 1997) Life-Time of
hadrons Hubble Time
e.g., Blasi Colafrancesco 1999
e.g., Schlickeiser 2002
Xm
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Radio Emission from secondary electrons/p
(e.g., Blasi Colafrancesco 1999, Dolag
Ensslin 2000, Brunetti Blasi 2005)
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Results on Upper Limits
(Brunetti et al., in prep)
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Results on Upper Limits
(Brunetti et al., in prep)
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Magnetic Field in Galaxy Clusters (FerettiGovoni
talks)
Dolag 2006
Vogt Ensslin 2005
Clarke et al. 2001
Magnetic field amplification by shear-flows
driven by accretion/mergers (e.g., Dolag et al.
2002-2006, Bruggen et al. 2005) Time scale of
the decay of the field is several Gyrs (i.e.,
other processes come into play) (e.g.,
Subramanian et al. 2006)
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A Radio-Based Approach

• Pro
• Deep radio data available
• Deep observations at low frequencies
• in 2-3 years (LOFAR)

Contro -Secondaries (e.g., Blasi
Colafrancesco 1999, Dolag Ensslin 2000) -
Shock Acceleration (e.g., Sarazin 1999, Dermer
Berrington 2005) - Stochastic Acceleration
(e.g., Schlickeiser et al. 1987) - Stochastic
RE-Acceleration (e.g., Brunetti et al. 2001,
Petrosian 2001, ...)
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A Radio-Based Approach

• Pro
• Deep radio data available
• Deep observations at low frequencies
• in 2-3 years (LOFAR)

Contro -Secondaries (e.g., Blasi
Colafrancesco 1999, Dolag Ensslin 2000) -
Shock Acceleration (e.g., Sarazin 1999, Dermer
Berrington 2005) - Stochastic Acceleration
(e.g., Schlickeiser et al. 1987) - Stochastic
RE-Acceleration (e.g., Brunetti et al. 2001,
Petrosian 2001, ...)
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Results I Origin of the emitting electrons
(Brunetti et al., in
prep)
z gt 0.2
Region of non Radio-emitting massive clusters
Present RH are inconsistent with the scenario of
secondary electrons
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A Radio-Based Approach
How to disentangle the contributions from
re-accelerated and from secondary particles ?
NCR
Nth
Synchrotron
e?
B
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Results II Limits on CR in Galaxy Clusters
(Brunetti et al., in prep)
Simulations
?2.9-3.3 (M2-2.3)
?2.1-2.3 (M3.8-6.4)
1
synchrotron
B
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Results II Limits on CR in Galaxy Clusters
(Brunetti et al., in prep)
?2.9-3.3
?2.1-2.3
synchrotron
B
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The Re-acceleration Model
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The RE-Acceleration Model
Brunetti et al. 2001 Petrosian 2001 Ohno et al.
2002 Kuo et al. 2003 Fujita, Takizawa, Sarazin
2003 Brunetti et al. 2004 Brunetti Blasi
2005 Cassano Brunetti 2005 Brunetti
Lazarian 2007
Turbulence
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Diffuse Radio Emission origin of emitting
electrons
Region of non Radio-emitting massive clusters
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The Re-acceleration Model
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The Re-acceleration Model
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The Re-acceleration Model
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Emission from CR in Galaxy Clusters
Pfrommer Ensslin 2004
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Radio Emission from secondary electrons/p
CR Confinement accumulation ubiquitous
slow decay of B (Dolag 2006 Subramanian et al.
2006) Radio Halos cannot be transient
phenomena Similar GC should have (statistically)
similar RH
Dolag 2004
Miniati et al. 2001
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Diffuse Radio Emission origin of emitting
electrons
Radio Halos are always found in merging
clusters (Buote 2001 Feretti 2004,05)
44
Thierbach al. 2002
Diffuse Radio Emission origin of emitting
electrons
Radio Halos have complex spectra (spectral
steepening, patchy spectral index) (Brunetti
2002,04 Petrosian 2002 Feretti et al. 2004,05
Orru et al. 2007)
Orru et al. 2007
45
Diffuse Radio Emission origin of emitting
electrons
Brunetti 2004
Govoni et al.,2001
Radio Halos are very extended (Govoni et al
2001 Brunetti 2002,04 Pfrommer Ensslin 2004
Marchegiani et al. 2007)
R? X0.6
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Searching for RH with GMRT at 610 Mhz
(Giacintucci et al. 2006 Venturi et al. 2007 )
Sample of 50 massive GC at z 0.2-0.4 (REFLEX
eBCS) Observations of 30 GC at GMRT
(610 MHz) down to brightness rms 0.03-0.1
mJy/beam Detection rate
of diffuse radio emission ?20
Upper limits
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Emission from CR in Galaxy Clusters
Protons are the dominant CR population in
Clusters (Voelk et al.1996 Berezinsky et al.
1997)
Blasi, Gabici, Brunetti,2007
CR Confinment for cosmological
time-scales enhances the possibility of p-p
collisions in the ICM a) ?-rays from ?o
decay b) Synchrotron from e c) IC from e

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Emission from CR in Galaxy Clusters
Protons are the dominant CR population in
Clusters (Voelk et al.1996 Berezinsky et al.
1997)
Blasi, Gabici, Brunetti,2007
CR Confinment for cosmological
time-scales enhances the possibility of p-p
collisions in the ICM a) ?-rays from ?o
decay b) Synchrotron from e c) IC from e

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Outline
Why Re-Acceleration ?? Re-Acceleration
Model HXR emission Simbol X