The Generation of The Generation of Magnetic Fields Magnetic Fields

and X-ray Observations and X-ray Observations

Yutaka FujitaYutaka FujitaNational Astronomical Observatory, JapanNational Astronomical Observatory, Japan

→ → Osaka University, JapanOsaka University, Japan

OutlineOutline

Generation of Magnetic Fields by the Generation of Magnetic Fields by the Weibel instabilityWeibel instability Y. Fujita & T. N. Kato Y. Fujita & T. N. Kato

(2005, MNRAS in press, astro-ph/0508589)(2005, MNRAS in press, astro-ph/0508589)

Japanese X-ray MissionsJapanese X-ray Missions

Weibel InstabilityWeibel 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

uz

uy

ux

ExampleExample

Numerical Simulation (Kato 2005)Numerical Simulation (Kato 2005) Weibel instability in a shockWeibel instability in a shock Full simulation (not MHD)Full simulation (not MHD)

Motion of each particle is calculatedMotion of each particle is calculated Electron-positron plasmaElectron-positron plasma

WallShockParticles

DensityDensity

BB

Wall

Characteristics of the Weibel Characteristics of the Weibel InstabilityInstability

Seed magnetic fields are not requiredSeed magnetic fields are not required

Short timescaleShort timescale pp

-1-1 1.81.81010-5 -5 ((nn/cm/cm-3-3))-0.5 -0.5 secsec

StrongStrong It can be saturated It can be saturated

only by nonlinear effectsonly by nonlinear effects

Okabe & Hattori (2003)

Evolution of Weibel InstabilityEvolution of Weibel Instability

Velocity anisotropy creates current filamentsVelocity anisotropy creates current filaments The currents create magnetic fieldsThe currents create magnetic fields

The evolution of the instability can be The evolution of the instability can be described by that of the currentsdescribed by that of the currents

B Currents

Medvedev et al. (2005)

Merger of CurrentsMerger of Currents

Currents with the same direction are Currents with the same direction are attracted because of their magnetic fieldsattracted because of their magnetic fields

Current and magnetic fields increase Current and magnetic fields increase through the merger of currentsthrough the merger of currents

Same Opposite

Saturation of Weibel InstabilitySaturation of Weibel Instability

Kato (2005)Kato (2005) Weibel instability saturates when currents Weibel instability saturates when currents

reach the Alfvreach the Alfvén currentén current

AlfvAlfvén currentén current IIAA==mcmc22v/e v/e ((v: v: bulk velocity, bulk velocity, mm: particle mass): particle mass) Maximum current allowed by the self-regulated Maximum current allowed by the self-regulated

Magnetic fieldsMagnetic fields

mnvB 2sat

v: shock velocityn: particle density, m: particle mass

Galaxy and Cluster Galaxy and Cluster Formation and the Weibel Formation and the Weibel

InstabilityInstabilityBased on the studies on the Based on the studies on the Weibel instability I have shown Weibel instability I have shown youyou

New IdeaNew Idea

We show that strong magnetic fields are inWe show that strong magnetic fields are instantaneously generated at the formation stantaneously generated at the formation of galaxies (and clusters)of galaxies (and clusters) Weibel instability at galactic-scale shocksWeibel instability at galactic-scale shocks

Schlickeiser & Shukla (2003) Weibel instability by electrons at z~0

We consider shocks at We consider shocks at zz1 and Weibel instability b1 and Weibel instability by protonsy protons

Hierarchical ClusteringHierarchical Clustering

Typical Mass of ObjTypical Mass of Objectsects 00=0.3, =0.3, =0.7, =0.7, hh==

0.7, 0.7, 88=0.9=0.9

Ts

Galactic ShocksGalactic Shocks

Shocks should be created at the time of Shocks should be created at the time of galaxy formationgalaxy formation

Tvir

Cosmologicalexpansion

Turn aroundLarge-scale structure (LSS) shocks

VirializationVirial shocks

(e.g. Cen & Ostriker 1999, Ryu et al. 2003)

Initial density fluctuation

Shock Mach NumberShock Mach Number

LSS shocksLSS shocks

(Furlanetto & Loeb 2004)(Furlanetto & Loeb 2004) Infall gas is coldInfall gas is cold Mach number Mach number 11Virial shocksVirial shocks

Mach number Mach number 44

pRzHv )(

vir/ rGMv

Temperature of the shocked gas

Virial Shock

LSS Shock

Magnetic Fields Generated by the Magnetic Fields Generated by the Weibel InstabilityWeibel Instability

If the shock Mach number is If the shock Mach number is 22 Anisotropy of the particle velocity distribution fu

nction (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 a(Silva et a

l. 2003)l. 2003)

ppP mnvB 2sat

Magnetic Fields Generated by the Magnetic Fields Generated by the Weibel InstabilityWeibel Instability

Magnetic field strengthMagnetic field strength B B 1010-7-71010-8-8GG

Strong amplification after the Strong amplification after the generation is not requiredgeneration is not required

Falls in a small rangeFalls in a small rangeConsistent with observationsConsistent with observations

Almost no evolutionAlmost no evolution In contrast with the dynamo In contrast with the dynamo

theorytheory

Strong magnetic fields at high Strong magnetic fields at high redshiftsredshifts May affect the formation of early May affect the formation of early

generation of stars and proto-generation of stars and proto-galaxiesgalaxies

Virial Shock

LSS Shock

PredictionsPredictions

High-redshift galaxiesHigh-redshift galaxies Strong magnetic fieldsStrong magnetic fields

Nearby clustersNearby clusters LSS shocks may be observed through synchrotron LSS shocks may be observed through synchrotron

emission and/or hard X-ray emission emission and/or hard X-ray emission ((SKA, NeXTSKA, NeXT))Those observations will tell us the positions of the LSS Those observations will tell us the positions of the LSS shocksshocks

Through the Weibel instability, magnetic fields are Through the Weibel instability, magnetic fields are generated in the plane of the shock frontgenerated in the plane of the shock front

PolarizationPolarization Magnetic fields should be observed only on the Magnetic fields should be observed only on the

downstream of the shockdownstream of the shockIntergalactic magnetic fields are not requiredIntergalactic magnetic fields are not required

`Missing Link’`Missing Link’

Weibel instabilityL ~ 1010 cmT ~ sec

Cluster Magnetic FieldsL ~ 1021 cmT ~ Gyr

??

Japanese X-ray MissionsJapanese X-ray Missions

SUZAKU (Astro-E2)SUZAKU (Astro-E2) Japan's fifth X-ray astronomy mission

in collaboration with U.S.

NeXTNeXT

SUZAKU (Astro-E2)SUZAKU (Astro-E2)SuzakuSuzaku is the is the recovery mission for recovery mission for ASTRO-EASTRO-E ASTRO-EASTRO-E did not did not

achieve orbit during achieve orbit during launch in 2000launch in 2000

SuzakuSuzaku was was launched in July 10launched in July 10

Launch (July 10)Launch (July 10)

The meaning of The meaning of SUZAKUSUZAKU

SUZAKUSUZAKU If it is written in Chinese CharactersIf it is written in Chinese Characters

　朱雀　朱雀　　　　　　　　　　 すざく すざく The direct translation of the Chinese The direct translation of the Chinese

Characters is Characters is Red SparrowRed Sparrow Suzaku is also a bird in Chinese mythology Suzaku is also a bird in Chinese mythology

The guardian of the southern skyThe guardian of the southern sky

Instruments Aboard Instruments Aboard SuzakuSuzaku

XRSXRS

XRS could give us ultra-high resolution spectraXRS could give us ultra-high resolution spectra For example, gas motion in clusters (For example, gas motion in clusters (100 km/s)100 km/s)

Turbulent cluster core(Fujita, Matsumoto, & Wada 2004)

The simulated X-ray Spectrum observed with XRS(Fujita et al. 2005)

Bold: with turbulenceThin: without turbulence

The Loss of XRSThe Loss of XRS

XRS uses liquid helium to cool the detectorXRS uses liquid helium to cool the detector

Unfortunately, the helium evaporated Unfortunately, the helium evaporated before the first light (Aug.8)before the first light (Aug.8) The cause is under investigationThe cause is under investigation

Observation schedule will be changed and Observation schedule will be changed and optimized to the remaining two detectors optimized to the remaining two detectors (XIS and HXD)(XIS and HXD)

Other InstrumentsOther InstrumentsXIS and HXD are working wellXIS and HXD are working well They will give us various information (e.g. hard X-ray They will give us various information (e.g. hard X-ray

from black holes, clusters of galaxies)from black holes, clusters of galaxies)

SNR (E0102-72.3)

XIS first light HXD first light

Centaurus A

SensitivitySensitivity

NeXT (New X-ray TelescopeNeXT (New X-ray Telescope ) )

Mission after Mission after SuzakuSuzaku

If the plan is approved, If the plan is approved, NeXTNeXT will be launched in will be launched in 20112011 Before the launches of Before the launches of Constellation-XConstellation-X and and XEUSXEUS

The Concept of The Concept of NeXTNeXT

PerformancePerformance

Effective area Sensitivity

NeXT

NeXT

ScienceScienceExampleExample Particle acceleration and magnetic fields in clustersParticle acceleration and magnetic fields in clusters

Cooperation with Cooperation with SKA SKA will be usefulwill be useful

A2256Radio image(Giovannini, Tordi, & Feretti 1999)

Simulated hard X-ray spectrumand image observed by NeXT

SynchrotronInverse Compton

Strong magnetite fields are generated at Strong magnetite fields are generated at shocks by the Weibel instability even at high shocks by the Weibel instability even at high redshifts (z~10)redshifts (z~10)

Two instruments on Two instruments on Suzaku Suzaku have just begun have just begun to make observationsto make observations

Never, never, never, never give up.Never, never, never, never give up.

　　 - - Winston ChurchillWinston Churchill

SummarySummary