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Gianfranco Brunetti

Gianfranco Brunetti

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Gianfranco Brunetti

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  1. The interplay of GeV electrons & magnetic fields:interesting aspects in galaxies, radio galaxies and clusters Gianfranco Brunetti Istituto di Radioastronomia – INAF, Bologna, ITALY

  2. Outline • Galactic radio halos: Bo, Brms, CRe diffusion • Physics of CRe acceleration in hot spots of radiogalaxies • Origin of CRe in giant radio halos from RM + γ-rays constraints • Radio halos in turbulent clusters and future LOFAR surveys clusters

  3. NGC 4631 (Krause 09) Galactic radio halos (see talk by Chyzy ..) NGC 253 (Heesen et al 09) Diffusion and transport of CRe perpendicular to the galactic plane .. - How extended ?? - Structure & strength of B on LS ?? - Winds/convection or diffusion ??

  4. Convection ?? V ~ 300 km/s NGC 253 (Heesen et al 09) Diffusion ?? D ~ 1029 cm2/s

  5. Testing diffusion models L Older electrons diffuse on larger scales and emit at lower frequencies … (??) Kolmogorov L -1/3(B/δB)

  6. Testing diffusion models L Older electrons diffuse on larger scales and emit at lower frequencies … (??) Bohm L B-1/2(B/δB)

  7. Radio galaxies (hot spots) Hot Spots: shock acceleration Lobes: evolution (and reacceleration?) Jets: transport & acceleration Bow shock (see talk by Saripalli, Orrù ..)

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

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

  10. Heavens & Meisenheimer 1989 B~100-500 μG Meisenheimer 1997; Brunetti +al. 2002 eLOFAR (50-100 MeV) Diffusive Shock Acceleration (Bell 1978; Eichler & Blandford 1987): GHz (~300 MeV)

  11. Heavens & Meisenheimer 1989 Amato & Arons 06 time mp/m±=100

  12. 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

  13. Clusters of galaxies: largest gravitational structures in the Universe (M1014-1015Msun RV 2-3 Mpc) 30-300 galaxies n10-3cm-3 T107-108K Galaxy cluster mass: Barions Dark Matter80% 5%of stars in galaxies 15-20% of hot diffuse gas

  14. Shocks van Weeren+al. 2010, Science Vazza, GB, Gheller ,09 Turbulence Pfrommer et al 06 Ryu, et al 2003 AGN/GW Raferty et al 06, Birzan et al. 07 Vazza, GB, et al 2009

  15. Shocks van Weeren+al. 2010, Science Vazza, GB, Gheller ,09 Turbulence AGN/GW Raferty et al 06, Birzan et al. 07 Vazza, GB, et al 2009

  16. In a fraction of merging clusters: Radio Halos “Bullet” cluster Govoni et al. 2004 COMA Brown & Rudnick 2011 1 Mpc Abell 2163 Feretti et al. 2001 RXCJ 2003-2525 Giacintucci et al. 2007

  17. The two leading mechanisms Miniati 2003 Hadronic interactions (Dennison 1980, Blasi & Colafrancesco 99, ..) FERMI High energy and neutrino emission from galaxy clusters GB & Lazarian 2011 Turbulence and stochastic (re)acceleration (Brunetti et al 01, Petrosian 01, many others..) Radio halos probe effects of plasma physics (non-linear interaction between Brms and particles) and the dissipation of energy in clusters mergers

  18. Gamma rays & origin of Radio Halos Lsyn~ f1(δ) <ECR> <Eth/T> Vsyn B(1+δ/2)(B2+Bcmb2)-1 Jeltema & Profumo 2011 Lγ,π~ f(δ) <ECR> <Eth/T> Vγ Ackermann et al 2010 USSRH Coma < >

  19. Further constraints from FERMI (GB, Blasi, Reimer, Rudnick, Bonafede et al. tbs) UB > 5-10 (UB)RM This suggests that secondaries due to p-p collisions do not play a leading role in the origin of radio halos B(r)=Bo(εTH/εo)η Syn spatial Profile 1.0 RM 0.5 0.2 FERMI RH scale  1 Mpc

  20. Gentle CRe acceleration mechanisms : turbulence/Fermi II ? Τ acc  1-3 108 yrs A 2256 Clarke & Ensslin 06 Heald et al 10 A 521 Coma GB et al 08 Brown & Rudnick 11

  21. Spectra of radio halos & turbulence Steepening frequency Χ1/τacc less efficient Big jumps = major mergers Small jumps = minor mergers Mergers between M>1015Msun Mergers between M<1015Msun more efficient 0.3 1.4 GHz

  22. Observed spectra of radio halos & turbulence Cassano, GB, Setti (2006) Steepening frequency Χ1/τacc less efficient Radio Halos with very steep spectrum in the classical radio band must exist 0.3 1.4 GHz

  23. Spectral properties of Radio Halos Cassano, GB, Rottgering, Bruggen, 2010 A&A 509 68 Tier 1 more energetics rare Radio Power less energetics common Frequency LOFAR is expected to discover 300-400 giant radio halos at z<1.0, a large fraction of them with very steep-spectrum (from less energetics cluster-cluster mergers)

  24. Conclusions • Total intensity & polarization observations provide information on CRe diffusion & Brms • Low frequency observations of radio hot spot constrain the low energy end of the spectrum of the accelerated CRe (injection problem) • FERMI γ-ray limits give constraint inconsistent with RM in case of hadronic models • LOFAR surveys will allow tests of turbulent reacceleration models for giant radio halos