Magnetic Fields Magnetic Fields and X-ray and X-ray Observations Observations Yutaka Fujita Yutaka Fujita National Astronomical Observatory, National Astronomical Observatory, Japan Japan → → Osaka University, Japan Osaka University, Japan
Jan 19, 2016
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