The structure of the pulsar magnetosphere via particle

  • Slides: 29
Download presentation
The structure of the pulsar magnetosphere via particle simulation Shinpei Shibata (1), Shinya Yuki

The structure of the pulsar magnetosphere via particle simulation Shinpei Shibata (1), Shinya Yuki (1), Tohohide Wada (2), Mituhiro Umizaki (1)Department of Phys. Yamagata University (2)National Astronomical Obvsevatory of Japan

Introduction Pulsars

Introduction Pulsars

Pulsars: B_d ~ 10^9 – 10^13 G P~ 1. 5 msec – several seconds

Pulsars: B_d ~ 10^9 – 10^13 G P~ 1. 5 msec – several seconds Emf~ 10^14 Volt particle acc. radaton: rotation powered pulsars Neutron Star about 1 M_sun 10 km in size magnetic powered pulsars Magnetars: Small subclass of magnetic neutron stars magnetic active regions with B~ (maybe)10^15 G

Rotation axis radiation is Beamed: observed as pulsed particles acc. by. E// Pulsar Wind

Rotation axis radiation is Beamed: observed as pulsed particles acc. by. E// Pulsar Wind 1 ly (relativistic outflow of magnetized plasma γ~ 10^6) Size of the magnetosphere: the light cylinder with R_L= c/Ω~ 4. 8× 10^4 R_ns

SED(spectral energy density plot) ke. V Ge. V Pulsed emission Te. V magnetospheric Size:

SED(spectral energy density plot) ke. V Ge. V Pulsed emission Te. V magnetospheric Size: RL=c/Ω Emf: Vacc=RL*BL =μΩ^2/c^2 Spectrum of beamed emission BB E// + e/p Curvature rad. byE// acceleration Unpulsed emission Nebula Rs=(Lwind/4πPext)^1/2 Vacc=Rs*Bn with Pext=Bn^2/8π sync IC Aharonian, F. A. & Atoyan, A. M. , 1998

What magnetospheric models to explain pulsed emission?

What magnetospheric models to explain pulsed emission?

Models based on observatons: PC, SG, OG Light cylinder Ω B Open Null surface

Models based on observatons: PC, SG, OG Light cylinder Ω B Open Null surface Polar cap field Clo (de sed f Dead ield ad zone zon e) region Outer gap Slot gap

Are all the three Models based on observatons: PC, correct? SG, OG if so,

Are all the three Models based on observatons: PC, correct? SG, OG if so, what is the mutual relation? γ-ray pulse shape and relation to radio pulses We attempted to solve this basic problem form the Light cylinder Ω B simulation. via particle are well explainedfirst if γprinciples from OG/SG. Radio from PC Open Radio pulse Null面 Polar cap field Clo (de sed f Dead ield ad zone zon e) Two-pole caustic (TPC) geometry (Dyks & Rudak, 2003) region Outer gap Slot gap

E// (field-aligned acceleration)

E// (field-aligned acceleration)

Unipolar Inductor Roation × magnetization makes emf >> gravity, work function E Magnetic neutron

Unipolar Inductor Roation × magnetization makes emf >> gravity, work function E Magnetic neutron star vacuume What is the fate of the particles which jump up into the magnetosphere simulation

By strong emf, charged particles are emitted from the neutron star and forms steady

By strong emf, charged particles are emitted from the neutron star and forms steady clouds. Rotation axis Polar domes of electrons Magnetic neutron star Equatorial disc with positive paritcles

- The clouds are corotating. E//=0 emf makes the gap - Vaccume gap E//

- The clouds are corotating. E//=0 emf makes the gap - Vaccume gap E// not zero vs (FFS) - Cloud-gap boundary is stable e+/e-pairs fills the gap Final (ref. Wada and Shibata 2003)state Map of E// E gap The gap is unstable against pair creation.

Particle simulation

Particle simulation

particle code Non neutral plasma acceleration ― E// appears Particle inertia is effective in

particle code Non neutral plasma acceleration ― E// appears Particle inertia is effective in the wind zone γ~ 10^7 Radiation reaction force Radiated photons make e+/e- pairs Gamma-ray Strong B radiation from the star ― ―

Particle code for the axis-symmetric steady solution, d /dt =0, Particle motion and the

Particle code for the axis-symmetric steady solution, d /dt =0, Particle motion and the electromagnetic fields are solved iteratively. For the EM field Emf is included in the BC For the particle motion

We use Grape-6, the special purpose computer for astrononomical Nbody problem at NAOJ. •

We use Grape-6, the special purpose computer for astrononomical Nbody problem at NAOJ. • Gravitational interaction • For the electric field • For the magnetic field

Particle creation and loss - Particles are emitted from the star if there is

Particle creation and loss - 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.

Results

Results

The outer gaps steadily create pairs with E// kept just above E> Ec. The

The outer gaps steadily create pairs with E// kept just above E> Ec. The proof of OG. Rotation axis Particle distribution and motion Pair creation Magnetic neutron star Light cylinder Strength of E// localized Outer gap Current sheet begins to form.

Global current in the meridional plane (do not forget plasma rotating and Bφ<0) Rotation

Global current in the meridional plane (do not forget plasma rotating and Bφ<0) Rotation axis Return current Sl Polar cap ot ga p Current-neutral dead zone Outer gap Fast rotation and Emition in φ-direction Outward current ( r ) Dead zone Magnetic neutron star Magnetic field (θ) Radiation reaction force (φ)

E>B (break down of the ideal-MHD cond. ), when we look at the inside

E>B (break down of the ideal-MHD cond. ), when we look at the inside of the current sheet. E/B map Light cylinder Uzdensky 2003 Force-free approximation also gives E>B

E>B (break down of the ideal-MHD cond. ), when we look at the inside

E>B (break down of the ideal-MHD cond. ), when we look at the inside of the current sheet. E/B map Light cylinder Umizaki et al. 2010 磁気リコネクショ ン

Summary 1. The outer gap, which is the candidate place of the particle acceleration

Summary 1. 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

Rotation axis Magnetic axis Light cylinder Ω Polar cap Slot gap Outer gap Thick wind

Rotation axis Magnetic axis Light cylinder Ω Polar cap Slot gap Outer gap Thick wind Neutral sheet Magnetic Reconnection Pulsar aurora

Basic properties of the pulsar magnetosphere 1. EMF and charge separation Unipolar Induction Motional

Basic properties of the pulsar magnetosphere 1. EMF and charge separation Unipolar Induction Motional field As compared with required charge separation, plasma source is limited  gap E//

In reality, plasma is extracted from the stellar surface by E//: maybe, complete charge

In reality, plasma is extracted from the stellar surface by E//: maybe, complete charge separation Negative space charge Corotation speed becomes the light speed Relativistic centrifugal wind Goldreich-Julian model (1969) Positive space charge

Strong charge separation in a rotating magnetosphere makes the gap, non-zero E// e c

Strong charge separation in a rotating magnetosphere makes the gap, non-zero E// e c a Negative space charge h c ll Nu f r u s e g r a Gap formation Goldreich-Julian model (1969) Positive space charge

SED(spectral energy density plot) ke. V Ge. V Pulsed emission Te. V magnetospheric RL=c/Ω

SED(spectral energy density plot) ke. V Ge. V Pulsed emission Te. V magnetospheric RL=c/Ω Vacc=RL*BL=μΩ^2/c^2 E// 加速 1. High Energy Pulses 3. Radio Pulses BB 加熱 E// + e/p 2. Pulsar Wind Lwind=ηw Lrot Unpulsed emission Nebula Rs=(Lwind/4πPext)^1/2 Vacc=Rs*Bn with Pext=Bn^2/8π 垂直衝撃波加速の困難 sync IC Aharonian, F. A. & Atoyan, A. M. , 1998