The structure of the pulsar magnetosphere via particle simulation
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Transcript of The structure of the pulsar magnetosphere via particle simulation
The structure of the pulsar magnetosphere via particle simulation
Shinpei Shibata (1), Shinya Yuki (1), Tohohide Wada (2),Mituhiro Umizaki (1)
(1)Department of Phys. Yamagata University(2)National Astronomical Obvsevatory of Japan
Introduction
Pulsars
Neutron Starabout 1M_sun10km in size
Pulsars:B_d ~ 10^9 – 10^13 GP ~ 1.5msec – several seconds
Emf ~ 10^14 Voltparticle acc. radaton: rotation powered pulsars
Magnetars: Small subclass of magnetic neutron starsmagnetic active regions with B ~ (maybe)10^15G
magnetic powered pulsars
Rotation axis
PulsarWind(relativisticoutflow ofmagnetizedplasmaγ ~ 10^6)
Size of the magnetosphere: the light cylinder with R_L= c/Ω ~ 4.8×10^4 R_ns
1 ly
radiation isBeamed:observed as pulsedparticles acc.byE//
SED(spectral energy density plot)
magnetospheric
Nebula
Aharonian, F.A. & Atoyan, A.M., 1998
Unpulsed emission
Pulsed emission
E// + e/p
BB
Curvature rad. by E // acceleration
IC
sync
Size: RL=c/Ω
Rs=(Lwind/4πPext)^1/2
Emf: Vacc=RL*BL
=μΩ^2/c^2
Vacc=Rs*Bn with Pext=Bn^2/8π
keVGeV
TeV
Spectrum of beamed emission
What magnetospheric models to explain pulsed emission?
Ω B
Dead zone
Null surface
Light cylinder
Polar cap
Slot gap
Outer gap
Models based on observatons: PC, SG, OG
Closed field(dead zone)
Open field region
Ω B
Dead zone
Null面
Light cylinder
Polar cap
Slot gap
Outer gapClosed field
(dead zone)
Open field region
γ-ray pulse shape and relation to radio pulses are well explained if γ from OG/SG. Radio from PC
Two-pole caustic (TPC) geometry (Dyks & Rudak, 2003)
Radio pulse
Models based on observatons: PC, SG, OGAre all the three correct?if so, what is the mutual relation?
We attempted to solve this basic problem form thefirst principles via particle simulation.
E// (field-aligned acceleration)
Roation × magnetizationmakes emf >> gravity, work function
Unipolar Inductor
E
What is the fate of the particles which jump up into the magnetosphere simulation
Magnetic neutron
starvacuume
By strong emf, charged particles are emitted from the neutron star and forms steady clouds.
Polar domes of electrons
Equatorial disc with positive paritcles
Magnetic neutron star
Rotation axis
- The clouds are corotating. E//=0- Vaccume gap E// not zero- Cloud-gap boundary is stable (FFS)
(ref. Wada and Shibata 2003)
gap
The gap is unstable against pair creation.
E
Map of E//
emf makes the gapvs
e+/e-pairs fills the gap Final state
Particle simulation
part
icle
code
―
acceleration
Gamma-ray―
―
radiation from the starStrong B
Particle codefor the axis-symmetric steady solution, d /dt =0, Particle motion and the electromagnetic fields are solved iteratively.
Emf is included in the BC
For the EM field
For the particle motion
• Gravitational interaction
• For the electric field • For the magnetic field
We use Grape-6, the special purpose computer for astrononomical N-body problem at NAOJ.
- Particles are emitted from the star if there is E// on the surface.
- On the spot approximation: e+/e- are created if E//>Ec
- Particles are removed through the outer boundary: loss by the puslar wind.
The system settles in a steady state when the system charge becomes constant:steadily pairs are created in the magnetosphere and lost as the wind.
Particle creation and loss
Results
Light cylinder
E// localized Outer gap
The outer gaps steadily create pairs with E// kept just above E> Ec . The proof of OG.
Particle distribution and motion Strength of E//
Pair creation
Rotation axis
Magnetic neutron starCurrent sheet begins to form.
Pola
r cap
Global current in the meridional plane(do not forget plasma rotating and Bφ<0)
Slot
gap
Outer gap
Return current
Current-neutral dead zone
Dead zone
Fast rotation andEmition in φ-direction
Outward current ( r )
Radiation reaction force (φ )
Magnetic field (θ)Magnetic neutron star
Rotation axis
Light cylinder
E/B mapE>B(break down of the ideal-MHD cond.), when we look at the inside of the current sheet.
Light cylinder
Uzdensky 2003
Force-free approximation also gives E>B
Light cylinder
E/B map
磁気リコネクション
Umizaki et al. 2010
E>B(break down of the ideal-MHD cond.), when we look at the inside of the current sheet.
Summary1. The outer gap, which is the candidate place of
the particle acceleration and gamma-ray emission, is proven from the first principles by particle simulation. OG, SG and PC, all exist self-consistently.
2. Due to radiation reaction force, some particles escape through the closed field lines.
3. At the top of the dead zone, we find strong E field larger than B, i.e., break down of the ideal-MHD condition, and in addition PIC simulation indicates reconnection driven by the centrifugal force.There are two places in which magnetic
reconnection may play an important role.-Close-open boundary near the light cylinder (Y-point)-Termination shock of the pulsar wind
Ω
Magnetic axis
Thick windNeutral sheet
Magnetic Reconnection
Pulsar aurora
Rotation axis
Lig
ht
cylin
der
Outer gap
Polar cap
Slot gap
1. EMF and charge separation
Unipolar Induction
Basic properties of the pulsar magnetosphere
Motional field
As compared with required charge separation, plasma source is limited gap E//
Goldreich-Julian model (1969)
In reality, plasma is extracted from the stellar surface by E//: maybe, complete charge separation
Positive space charge
Negative space charge
Corotation speed becomes the light speed
Relativistic
centrifugal wind
Goldreich-Julian model (1969)
Strong charge separation in a rotating magnetosphere makes the gap, non-zero E//
Positive space charge
Negative space charge Null c
harge surfa
ce
Gap formation
SED(spectral energy density plot)
magnetospheric
Nebula
2. Pulsar Wind Lwind=ηw Lrot
Aharonian, F.A. & Atoyan, A.M., 1998
Unpulsed emission
Pulsed emission
E// + e/p
BB 加熱
E // 加速
IC
sync
RL=c/Ω
Rs=(Lwind/4πPext)^1/2
Vacc=RL*BL=μΩ^2/c^2
Vacc=Rs*Bn with Pext=Bn^2/8π
keVGeV
TeV
垂直衝撃波加速の困難
1. High Energy Pulses1. High Energy Pulses3. Radio Pulses