lofar & particle acceleration: radio galaxies & galaxy clusters gianfranco brunetti...
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LOFAR & Particle Acceleration: LOFAR & Particle Acceleration: Radio Galaxies & Galaxy ClustersRadio Galaxies & Galaxy Clusters
Gianfranco Gianfranco BrunettiBrunettiInstitute of Radioastronomy –INAF, Bologna,
ITALY
Outline
Particle acceleration mechanisms drive the properties and evolution of radio sources.
The efficiency of these mechanisms depends on micro-physics
Radio Galaxies (shocks, particle and source evolution)
Galaxy Clusters (shocks, turbulence)
Particle Acceleration@ HS (min energy)
Energetics of Radio Lobes
Evolution of B & Relativisticparticles in Radio Lobes
Hot Spots: shockacceleration
Lobes: evolution(and reacceleration?)
Jets: transport &acceleration
Bow shock
Electrons (& p) Acceleration :
High energy electrons (emission)
Polarisation and intensity
Heavens & Meisenheimer 1989
Prieto+Brunetti+Mack 2002
Heavens & Meisenheimer 1989
Meisenheimer 1997; Brunetti +al. 2002
Diffusive Shock Acceleration (Bell 1978; Eichler & Blandford 1987):
Lazio, Kassim +al. 2006
Measurements of low-energy cut-off ?
This has fundamental implications on the theory of particle acceleration andon the energetics of radio sources: Science Case for Long Baseline LOFAR
See alsoBlundell +al. 2006(6C 0905+3955)
br22 )1(
1syn
zBB
B
IC
Parma +al. 1999
In case of smooth transportand diffusion of relativisticplasma in Radio Lobes :Spectral Ageing
This holds only for constant B.Gradients in B may produce spectral variations similar to Ageing (Blundell & Rawlings 2000)
B
Spectrum
Syn
Science case for Long Baseline LOFAR
Arcsec resolution spatially resolved spectral studies at low radio frequencies
MHD Simulations+Relativistic particles(Tregillis +al. 2001, 2004)
Possible detection with LOFAR within0.2 to 0.3 Gyrs from switch-off & expansion, this also constrains the max size of these Relic-Radio Galaxies Kaiser & Cotter 2002
Now LOFAR
Large Scale Shocks may efficiently boost up Ghost-radio plasma via adiabatic compression in case this plasma is not efficiently mixed with the IGM (Ensslin & Gopal-Krishna 2001)
Ensslin & Bruggen 2002
Shocks in Galaxy Clusters
Vazza, Brunetti, Gheller 2008
Relics: Acceleration of CRe at shocks(e.g., Ensslin+al.1998; Hoeft & Bruggen 2007)
Bagchi+al. 2002
Pfrommer +al. 2006
Battaglia +al. 2008
Steep SpectrumRadio Sources
Acceleration of CR at shockspinj is a “poorly constrained quantity” …
However going from pinj = 3.5 pth to 3.8 reduces the acceleration efficiency by a factor of 10 !
(Kang & Jones 2002; see also Malkov 1997, Kang & Jones 2005, 07, Amato & Blasi 2006)
protons
The efficiency of CR shockacceleration depends on theMach number. Electrons “reasonably” got a small fraction of this energy (0.01..).
LOFAR will put fundamentalconstraints on particle acceleration at weak shocks.
Ryu et al. 2003
Kang & Jones 2007
SN
1-
2-
Radio HalosRadio Halos
GeV electrons on Mpc scales
μG magnetic fields on Mpc scales
Tdiff
(~1010 yr) >> Tcool
(~108 yr)
(Jaffe 1977)
Labs to study GC as particle accelerators
Secondary particles, relativistic electrons continuously injected in the ICM by inelastic proton-proton collisions through productions and decay of charged pions (e.g., Dennison 1980, Blasi & Colafrancesco 1999, Dolag & Ensslin 2000,Pfrommer+al.2008)
In situ re-acceleration by MHD turbulence developed in the cluster volume during the merger events (e.g., Brunetti et al. 2001, 2004; Petrosian 2001; Ohno et al. 2002; Fujita et al. 2003; Brunetti & Blasi 2005; Brunetti & Lazarian 2007; Petrosian & Bykov 2008)
p,e±
Thierbach +al. 2002
Observations: Spectral Cut-Off
Slicheiser +al. 1987 (Coma) Evidence of break in the
synchrotron spectrum
F()
Thierbach +al. 2002
Observations: Spectral Cut-Off
Slicheiser +al. 1987 (Coma)
Evidence of break in thespectrum of the emittingelectrons at energies offew GeV
Re-acceleration
losses
F()
Acceleration mechanism notefficient !
acceleration
p,e±
Brunetti+Blasi 2005; Brunetti+al. 2008Increasing theimportance of turbulence
synδ/2
Forbidden region for hadronicmodels at syn> 1.4-1.5
syn=1.6
Hadronic Origin
Brunetti 2004Brentjens 2008
Cassano +al. 2006, 2008They probably exist
B
Radial
Spectral index maps of Radio Halos
B
Radial
Spectral index maps of Radio Halos
B
RadialOrru’ +al. 2007
Optimal UV coverage onRH scales at several frequencies …
Conclusions
LOFAR will provide a unique possibility to investigate particle acceleration in extragalactic radio sources and to constrain their physics (and micro-physics)
Radio Galaxies : - low energy end of the spectrum of electrons accelerated at shocks
- energetics evolution and composition of the relativistic plasma
- Relic/Dying Radio Galaxies
Galaxy Clusters : efficiency of electron acceleration at weak shocks
- origin of large scale diffuse emission in Clusters
- Searching for Ultra-Steep-Spectrum Radio Halos