lofar & particle acceleration: radio galaxies & galaxy clusters gianfranco brunetti...

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