1. LOFAR & Particle Acceleration: Radio Galaxies & Galaxy Clusters
Gianfranco Brunetti
Institute of Radioastronomy –INAF, Bologna, ITALY

2. 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)

3. 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

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

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

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

7. 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)

8. 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

9. 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

10. 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

11. Shocks in Galaxy Clusters
Vazza, Brunetti, Gheller 2008

12. 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

13. Acceleration of CR at shocks
protons
pinj is a “poorly constrained quantity” …
However going from pinj = 3.5 pth to reduces the
acceleration efficiency by a factor of 10 !
(Kang & Jones 2002; see also Malkov 1997, Kang & Jones 2005, 07, Amato & Blasi 2006)

14. 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

15. 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

16. 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±

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

18. 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

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

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

21. Cassano +al. 2006, 2008
They probably exist

22. Spectral index maps of Radio HalosB
Radial

23. Spectral index maps of Radio HalosB
Radial

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

25. 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