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The Generation of Magnetic Fields and X-ray Observations

The Generation of Magnetic Fields and X-ray Observations. Yutaka Fujita National Astronomical Observatory, Japan → Osaka University, Japan. Outline. Generation of Magnetic Fields by the Weibel instability Y. Fujita & T. N. Kato (2005, MNRAS in press, astro-ph/0508589)

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The Generation of Magnetic Fields and X-ray Observations

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  1. The Generation of Magnetic Fields and X-ray Observations Yutaka Fujita National Astronomical Observatory, Japan → Osaka University, Japan

  2. Outline • Generation of Magnetic Fields by the Weibel instability • Y. Fujita & T. N. Kato (2005, MNRAS in press, astro-ph/0508589) • Japanese X-ray Missions

  3. uz uy ux Weibel Instability • The Weibel instability is driven in a collisionless plasma by the anisotropy of the particle velocity distribution function (PDF) of the plasma • Shocks • Strong temperature gradient • Magnetic fields are generated so that the PDF becomes isotropic • Particle orbits are deflected by the magnetic fields

  4. Example • Numerical Simulation (Kato 2005) • Weibel instability in a shock • Full simulation (not MHD) • Motion of each particle is calculated • Electron-positron plasma Particles Wall Shock

  5. Wall • Density • B

  6. Characteristics of the Weibel Instability • Seed magnetic fields are not required • Short timescale • p-1 1.810-5 (n/cm-3)-0.5 sec • Strong • It can be saturated only by nonlinear effects Okabe & Hattori (2003)

  7. Evolution of Weibel Instability • Velocity anisotropy creates current filaments • The currents create magnetic fields • The evolution of the instability can be described by that of the currents Medvedev et al. (2005) B Currents

  8. Merger of Currents • Currents with the same direction are attracted because of their magnetic fields • Current and magnetic fields increase through the merger of currents Same Opposite

  9. Saturation of Weibel Instability • Kato (2005) • Weibel instability saturates when currents reach the Alfvén current • Alfvén current • IA=mc2v/e (v: bulk velocity, m: particle mass) • Maximum current allowed by the self-regulated Magnetic fields v: shock velocity n: particle density, m: particle mass

  10. Galaxy and Cluster Formation and the Weibel Instability • Based on the studies on the Weibel instability I have shown you

  11. New Idea • We show that strong magnetic fields are instantaneously generated at the formation of galaxies (and clusters) • Weibel instability at galactic-scale shocks • Schlickeiser & Shukla (2003) • Weibel instability by electrons at z~0 • We consider shocks at z1 and Weibel instability by protons

  12. Hierarchical Clustering • Typical Mass of Objects • 0=0.3, =0.7, h=0.7, 8=0.9

  13. Galactic Shocks • Shocks should be created at the time of galaxy formation Initial density fluctuation Ts Tvir Cosmological expansion Virialization Virial shocks Turn around Large-scale structure (LSS) shocks (e.g. Cen & Ostriker 1999, Ryu et al. 2003)

  14. Shock Mach Number Temperature of the shocked gas • LSS shocks (Furlanetto & Loeb 2004) • Infall gas is cold • Mach number 1 • Virial shocks • Mach number 4 Virial Shock LSS Shock

  15. Magnetic Fields Generated by the Weibel Instability • If the shock Mach number is 2 • Anisotropy ofthe particle velocity distribution function (PDF) is large enough • v: shock velocity, np: proton density, mp: proton mass (Kato2005) • Correction factor, P0.5 • From simulations (Kato 2005) • Final magnetic fields, Bf ~ 0.1 Bsat (Silva et al. 2003)

  16. Magnetic Fields Generated by the Weibel Instability • Magnetic field strength • B 10-710-8G • Strong amplification after the generation is not required • Falls in a small range • Consistent with observations • Almost no evolution • In contrast with the dynamo theory • Strong magnetic fields at high redshifts • May affect the formation of early generation of stars and proto-galaxies Virial Shock LSS Shock

  17. Predictions • High-redshift galaxies • Strong magnetic fields • Nearby clusters • LSS shocks may be observed through synchrotron emission and/or hard X-ray emission (SKA, NeXT) • Those observations will tell us the positions of the LSS shocks • Through the Weibel instability, magnetic fields are generated in the plane of the shock front • Polarization • Magnetic fields should be observed only on the downstream of the shock • Intergalactic magnetic fields are not required

  18. Weibel instability • L ~ 1010 cm • T ~ sec Cluster Magnetic Fields • L ~ 1021 cm • T ~ Gyr ?? `Missing Link’

  19. Japanese X-ray Missions • SUZAKU (Astro-E2) • Japan's fifth X-ray astronomy mission • in collaboration with U.S. • NeXT

  20. SUZAKU (Astro-E2) • Suzaku is the recovery mission for ASTRO-E • ASTRO-E did not achieve orbit during launch in 2000 • Suzaku was launched in July 10

  21. Launch (July 10)

  22. The meaning of SUZAKU • SUZAKU • If it is written in Chinese Characters 　朱雀 すざく • The direct translation of the Chinese Characters is Red Sparrow • Suzaku is also a bird in Chinese mythology • The guardian of the southern sky

  23. Instruments Aboard Suzaku

  24. XRS • XRS could give us ultra-high resolution spectra • For example, gas motion in clusters (100 km/s) Bold: with turbulence Thin: without turbulence The simulated X-ray Spectrum observed with XRS (Fujita et al. 2005) Turbulent cluster core (Fujita, Matsumoto, & Wada 2004)

  25. The Loss of XRS • XRS uses liquid helium to cool the detector • Unfortunately, the helium evaporated before the first light (Aug.8) • The cause is under investigation • Observation schedule will be changed and optimized to the remaining two detectors (XIS and HXD)

  26. Other Instruments • XIS and HXD are working well • They will give us various information (e.g. hard X-ray from black holes, clusters of galaxies) XIS first light HXD first light SNR (E0102-72.3) Centaurus A

  27. Sensitivity

  28. NeXT (New X-ray Telescope ) • Mission after Suzaku • If the plan is approved, NeXT will be launched in 2011 • Before the launches of Constellation-X and XEUS

  29. The Concept of NeXT

  30. Performance NeXT NeXT Sensitivity Effective area

  31. Science • Example • Particle acceleration and magnetic fields in clusters • Cooperation with SKA will be useful Synchrotron Inverse Compton A2256 Radio image (Giovannini, Tordi, & Feretti 1999) Simulated hard X-ray spectrum and image observed by NeXT

  32. Summary • Strong magnetite fields are generated at shocks by the Weibel instability even at high redshifts (z~10) • Two instruments on Suzaku have just begun to make observations Never, never, never, never give up. - Winston Churchill

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