LOFAR & Particle Acceleration: Radio Galaxies & Galaxy Clusters Gianfranco Brunetti Institute 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 Hot Spots: shock acceleration Lobes: evolution (and reacceleration?) Jets: transport & acceleration Bow shock Particle Acceleration @ HS (min energy) Energetics of Radio Lobes Evolution of B & Relativistic particles in Radio Lobes

Electrons (& p) Acceleration : High energy electrons (emission) Heavens & Meisenheimer 1989 Prieto+Brunetti+Mack 2002 Electrons (& p) Acceleration : High energy electrons (emission) Polarisation and intensity

Heavens & Meisenheimer 1989 Meisenheimer 1997; Brunetti +al. 2002 Diffusive Shock Acceleration (Bell 1978; Eichler & Blandford 1987):

Measurements of low-energy cut-off ? Lazio, Kassim +al. 2006 See also Blundell +al. 2006 (6C 0905+3955) This has fundamental implications on the theory of particle acceleration and on the energetics of radio sources: Science Case for Long Baseline LOFAR

Parma +al. 1999 In case of smooth transport and diffusion of relativistic plasma in Radio Lobes : Spectral Ageing This holds only for constant B. Gradients in B may produce spectral variations similar to Ageing (Blundell & Rawlings 2000)

MHD Simulations+Relativistic particles (Tregillis +al. 2001, 2004) Arcsec resolution spatially resolved spectral studies at low radio frequencies Syn B Spectrum Science case for Long Baseline LOFAR

LOFAR Now Possible detection with LOFAR within 0.2 to 0.3 Gyrs from switch-off & expansion, this also constrains the max size of these Relic-Radio Galaxies Kaiser & Cotter 2002

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) Pfrommer +al. 2006 Bagchi+al. 2002 Battaglia +al. 2008 Steep Spectrum Radio Sources

Acceleration of CR at shocks protons pinj 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)

1- 2- The efficiency of CR shock acceleration depends on the Ryu et al. 2003 Kang & Jones 2007 The efficiency of CR shock acceleration depends on the Mach number. Electrons “reasonably” got a small fraction of this energy (0.01..). LOFAR will put fundamental constraints on particle acceleration at weak shocks. 1- 2- SN

Radio Halos Labs to study GC as particle accelerators 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±

Observations: Spectral Cut-Off Slicheiser +al. 1987 (Coma) Evidence of break in the synchrotron spectrum Thierbach +al. 2002

Observations: Spectral Cut-Off Evidence of break in the spectrum of the emitting electrons at energies of few GeV Slicheiser +al. 1987 (Coma) Acceleration mechanism not efficient ! Re-acceleration Thierbach +al. 2002 losses acceleration

Brunetti+Blasi 2005; Brunetti+al. 2008 Increasing the importance of turbulence p,e±

Hadronic Origin synδ/2 Forbidden region for hadronic models at Brunetti 2004 Brentjens 2008 Forbidden region for hadronic models at syn> 1.4-1.5 syn=1.6

Cassano +al. 2006, 2008 They probably exist

Spectral index maps of Radio Halos B Radial

Spectral index maps of Radio Halos B Radial

Optimal UV coverage on RH scales at several frequencies … B Radial Orru’ +al. 2007 Optimal UV coverage on RH 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