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Inverse Compton Hard X-rays from Galaxy Clusters

Inverse Compton Hard X-rays from Galaxy Clusters. Gianfranco Brunetti INAF-Istituto di Radioastronomia, Bologna, Italy Rossella Cassano Universita’ di Bologna & INAF-IRA Giancarlo Setti Universita’ di Bologna & INAF-IRA. The RE-Acceleration Model

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Inverse Compton Hard X-rays from Galaxy Clusters

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  1. Inverse Compton Hard X-rays from Galaxy Clusters Gianfranco Brunetti INAF-Istituto di Radioastronomia, Bologna, Italy Rossella Cassano Universita’ di Bologna & INAF-IRA Giancarlo Setti Universita’ di Bologna & INAF-IRA

  2. The RE-Acceleration Model (Brunetti et al. 2001, Petrosian 2001,…++ al.) IC MF Amplification Turbulence Synchrotron

  3. Theoretically … Galaxy Clusters are Lab for stochastic particle acceleration (e.g. Brunetti & Lazarian 2007) Suitable combination of : Beta of plasma (large) Turbulent media Long ion mean free path (collisionless) Large-scale magnetised systems Long time-scales

  4. Diffuse Radio Emission & in situ electron acceleration Radio Halos are rare (Hwang 2004) Radio Halos are always found in merging clusters (Buote 2001; Feretti 2004,05) Radio Halos have complex spectra (spectral steepening, patchy spectral index) (Brunetti 2002,04; Petrosian 2002; Feretti et al. 2004,05; Orru’ et al. 2007) Radio Halos are very extended (Govoni et al 2001; Brunetti 2002,04; Pfrommer & Ensslin 2004; Marchegiani et al. 2007)

  5. Diffuse Radio Emission & origin of emitting electrons In the RE-Acceleration Scenario RH (& HXR) should be Transient

  6. Diffuse Radio Emission & origin of emitting electrons In the RE-Acceleration Scenario RH (& HXR) should be Transient

  7. Diffuse Radio Emission & origin of emitting electrons In the RE-Acceleration Scenario RH (& HXR) should be Transient

  8. Diffuse Radio Emission & origin of emitting electrons GMRT (T.Venturi et al.2007;GB et al.) Sample of 50 massive GC at z =0.2-0.4 (REFLEX + eBCS) Similar z Similar masses/temperature Similar X-ray luminosities

  9. Diffuse Radio Emission & origin of emitting electrons GMRT (T.Venturi et al.2007;GB et al.) Radio loud Radio quiet

  10. IC HXR from the RE-Acceleration Model For suitable (but viable) conditions the IC from re-accelerated electrons/positrons can match the observed HXRs There is a big degeneracy in the synchrotron expectations (synchrotron degeneracy) Brunetti & Blasi 2005

  11. Cassano & Brunetti 2005; Cassano et al. 2006 HXR: Calculations vi M1 M2 Merging Trees Efm~fm vi2 Turbulent injection Particle Acceleration

  12. Cassano & Brunetti 2005; Cassano et al. 2006 HXR: Calculations BMb

  13. BMb

  14. Consequence: HXR: Results Luminosity Functions Number Counts z=0.05 z=0.25 z=0.45 HXR Tails (from re-accelerated electrons in Mpc regions) are produced in massive clusters, Mvir >1015Mo

  15. Consequence: HXR: Results Luminosity Functions Number Counts z=0.05 z=0.25 z=0.45 HXR Tails (from re-accelerated electrons in Mpc regions) are produced in massive clusters, Mvir >1015Mo BeppoSAX

  16. Consequence: HXR: Results Luminosity Functions Simbol-X Number Counts z=0.05 z=0.25 z=0.45 HXR Tails (from re-accelerated electrons in Mpc regions) are produced in massive clusters, Mvir >1015Mo BeppoSAX

  17. Consequence: HXR: Results Redshift distribution The bulk of HXR tails from re-accelerated particles is expected at z=0-0.2 for typical Simbol X surveys Shallow surveys are expected to catch only local HXR tails F[ ]>10-13 cgs F[ ]>5*10-13 cgs F[ ]>10-12 cgs

  18. Conclusions Presently known RH are probably complex and transient (re-acceleration scenario..), they are probably just the tip of the iceberg . Present Modelling of particle re-acceleration may provide first expectations for IC HXR Tails emitted from the re-accelerated electrons/positrons Catching IC signals from Galaxy Clusters is important to break the synchrotron degeneracy (Particle-Field) In case the HXR Tails discovered by BeppoSAX & RXTE are all real SIMBOL-X should catch HXR Tails from 10-100 massive Galaxy Clusters at z=0.0-0.2

  19. Conclusions Presently known RH are probably complex and transient (re-acceleration scenario..), they are probably just the tip of the iceberg . Present Modelling of particle re-acceleration may provide first expectations for IC HXR Tails emitted from the re-accelerated electrons/positrons Catching IC signals from Galaxy Clusters is important to break the synchrotron degeneracy (Particle-Field) In case the HXR Tails discovered by BeppoSAX & RXTE are all real SIMBOL-X should catch HXR Tails from 10-100 massive Galaxy Clusters at z=0-0.2

  20. Diffuse Radio Emission & origin of emitting electrons MF is ubiquitous in GC CRp & secondaries are ubiquitous Miniati et al. 2001

  21. Kinetic Fully Non-linear Wave--Particle Coupling (Brunetti +al. 2004; Brunetti & Blasi 2005; Brunetti & Lazarian 2007) Waves spectra Electron spectra Ee = 0.001 Eth Ep = 0.005 Eth s=3.2 Proton spectra

  22. Cassano & Brunetti 2005; Cassano et al. 2006 HXR: Calculations Simplified Plasma Physics & Simplified Cosmological formalism (E-PS) Merging Trees Turbulent injection Particle Acceleration

  23. CR in Galaxy Clusters CR Confinment in Galaxy Clusters (e.g., Voelk et al. 1996, Berezinsky et al. 1997) Life-Time of hadrons ~ Hubble Time e.g., Blasi & Colafrancesco 1999 e.g., Schlickeiser 2002 Xm=

  24. Radio Emission from secondary electrons/p (e.g., Blasi & Colafrancesco 1999, Dolag & Ensslin 2000, Brunetti & Blasi 2005)

  25. Results on Upper Limits (Brunetti et al., in prep)

  26. Results on Upper Limits (Brunetti et al., in prep)

  27. Magnetic Field in Galaxy Clusters (Feretti+Govoni talks) Dolag 2006 Vogt & Ensslin 2005 Clarke et al. 2001 Magnetic field amplification by shear-flows driven by accretion/mergers (e.g., Dolag et al. 2002-2006, Bruggen et al. 2005) Time scale of the decay of the field is several Gyrs (i.e., other processes come into play) (e.g., Subramanian et al. 2006)

  28. A Radio-Based Approach Pro : Deep radio data available • Deep observations at low frequencies • in 2-3 years (LOFAR) Contro : -Secondaries (e.g., Blasi & Colafrancesco 1999, Dolag & Ensslin 2000) - Shock Acceleration (e.g., Sarazin 1999, Dermer & Berrington 2005) - Stochastic Acceleration (e.g., Schlickeiser et al. 1987) - Stochastic RE-Acceleration (e.g., Brunetti et al. 2001, Petrosian 2001, ...)

  29. A Radio-Based Approach Pro : Deep radio data available • Deep observations at low frequencies • in 2-3 years (LOFAR) Contro : -Secondaries (e.g., Blasi & Colafrancesco 1999, Dolag & Ensslin 2000) - Shock Acceleration (e.g., Sarazin 1999, Dermer & Berrington 2005) - Stochastic Acceleration (e.g., Schlickeiser et al. 1987) - Stochastic RE-Acceleration (e.g., Brunetti et al. 2001, Petrosian 2001, ...)

  30. Results I: Origin of the emitting electrons (Brunetti et al., in prep) z > 0.2 Region of non Radio-emitting massive clusters Present RH are inconsistent with the scenario of secondary electrons

  31. A Radio-Based Approach How to disentangle the contributions from re-accelerated and from secondary particles ? NCR Nth Synchrotron e B

  32. Results II: Limits on CR in Galaxy Clusters (Brunetti et al., in prep) Simulations =2.9-3.3 (M=2-2.3) =2.1-2.3 (M=3.8-6.4) 1 synchrotron B

  33. Results II: Limits on CR in Galaxy Clusters (Brunetti et al., in prep) =2.9-3.3 =2.1-2.3 synchrotron B

  34. e- p+ e- e+ The Re-acceleration Model

  35. The RE-Acceleration Model Brunetti et al. 2001; Petrosian 2001 Ohno et al. 2002; Kuo et al. 2003; Fujita, Takizawa, Sarazin 2003; Brunetti et al. 2004; Brunetti & Blasi 2005; Cassano & Brunetti 2005; Brunetti & Lazarian 2007 Turbulence

  36. Diffuse Radio Emission & origin of emitting electrons Region of non Radio-emitting massive clusters

  37. Turbulence Shocks e- p+ e- p+ e- e+ The Re-acceleration Model

  38. Turbulence Shocks e- p+ e- p+ e- e+ The Re-acceleration Model

  39. Turbulence Shocks e- p+ e- p+ e- e+ The Re-acceleration Model

  40. Emission from CR in Galaxy Clusters Pfrommer & Ensslin 2004

  41. Radio Emission from secondary electrons/p CR Confinement & accumulation + ubiquitous & slow decay of B (Dolag 2006; Subramanian et al. 2006) Radio Halos cannot be transient phenomena Similar GC should have (statistically) similar RH Dolag 2004 Miniati et al. 2001

  42. Diffuse Radio Emission & origin of emitting electrons Radio Halos are always found in merging clusters (Buote 2001; Feretti 2004,05)

  43. Thierbach +al. 2002 Diffuse Radio Emission & origin of emitting electrons Radio Halos have complex spectra (spectral steepening, patchy spectral index) (Brunetti 2002,04; Petrosian 2002; Feretti et al. 2004,05; Orru’ et al. 2007) Orru’ et al. 2007

  44. Diffuse Radio Emission & origin of emitting electrons Brunetti 2004 Govoni et al.,2001 Radio Halos are very extended (Govoni et al 2001; Brunetti 2002,04; Pfrommer & Ensslin 2004; Marchegiani et al. 2007) R X0.6

  45. Searching for RH with GMRT at 610 Mhz (Giacintucci et al. 2006; Venturi et al. 2007; …) Sample of 50 massive GC at z =0.2-0.4 (REFLEX + eBCS) Observations of ~30 GC at GMRT (610 MHz) down to brightness rms ~ 0.03-0.1 mJy/beam Detection rate of diffuse radio emission 20% Upper limits

  46. Emission from CR in Galaxy Clusters Protons are the dominant CR population in Clusters (Voelk et al.1996; Berezinsky et al. 1997) Blasi, Gabici, Brunetti,2007 CR Confinment for cosmological time-scales enhances the possibility of p-p collisions in the ICM a) -rays fromo decay b) Synchrotron from e± c) IC from e±

  47. Emission from CR in Galaxy Clusters Protons are the dominant CR population in Clusters (Voelk et al.1996; Berezinsky et al. 1997) Blasi, Gabici, Brunetti,2007 CR Confinment for cosmological time-scales enhances the possibility of p-p collisions in the ICM a) -rays fromo decay b) Synchrotron from e± c) IC from e±

  48. Outline Why Re-Acceleration ?? Re-Acceleration Model HXR emission & Simbol X

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