Photospheric emission from Structured Jet

Hirotaka Ito

　　 Collaborators

Shigehiro Nagataki 　　 YITP 　

＠ YITP Lunch Seminar　 2012 5/30

Shoichi Yamada 　 Waseda University　

Gamma-Ray Burst (GRB)

・ duration

T ~ 10ms ー 100s

・ rapid variability

δt ～ ms

Most luminous explosion in the universe

Lγ,iso ~ 1052 erg/s

Time (s)

Co

un

ts/s

・ event rate

~1000/yr

Briggs + 1999

<α>~ -0.9

β~ -2.5

νν^(-0.5)

Band function

< Ep > ~ 160 keV

< Ep > ~ 490 keV

Long GRB

Short GRB

α~ -1

<α>~ -0.5

<β>~ -2.3Nava + 2011

Fν ν∝ -α 　（ hν< Ep ）Fν ν∝ -β 　（ hν> Ep ）

Prompt Emission Spectrum

Model for Emission Mechanism Internal Shock Model

Photospheric Emission Model

photosphere Internal shockExternal shock

γ γ

・ Low efficiency for gamma-ray production

・ too hard spectrum in low energy band (α)

GRB090902B

(e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007)

flaw

photosphere Internal shockExternal shock

γ γ

低エネルギースペクトルを説明(e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007)

flaw:　 high energy non-thermal tail（ β）

Model for Emission Mechanism Internal Shock Model

Photospheric Emission Model

・ Low efficiency for gamma-ray production

・ too hard spectrum in low energy band (α)flaw

Spine-Sheath jet

Spine

τ~1

0 >> 1

1 >> 1

Present Study

Sheath

Photosphere

0 > 1

Photon acceleration in a structured jet as a mechanism for production of non-thermal tail

Spine

τ~1

0 >> 1

1 >> 1

Photons gain energy by crossing the boundary layer

Sheath

PhotosphereAccleration region

We solve the propagation of photons within the spine sheath jet

0 > 1

Present StudyPhoton acceleration in a structured jet as a mechanism for

production of non-thermal tail

Spine-Sheath jet

r

Spine (θ<θ0 ) Sheath (θ0<θ<θj )

Calculation Range

rin << Rph

rout = 500Rph(τ~2×10-3)

rin (τ>>1)

rout (τ<<1)

Model

:photospheric radius

VelocitySpine-Sheath

Electron number density

r

Spine (θ<θ0 ) Sheath (θ0<θ<θj )

Initial Condition

Inject thermal photons at the inner boundary

rin (τ>>1)

rout (τ<<1)

Model

Lin = 5.4×1052 r82/3400

8/3 L531/3 (rin/1011cm)-2/3 erg/s

Tin = 0.9 r81/6400

8/3 L53-5/12 (rin/1011cm)-2/3 keV

Propagation of photons are solved by Monte=Carlo method

VelocitySpine-Sheath

Electron number density

Emax = 0mec2

Klein-Nishina cut-off

Spine

Sheath

Thermal + non-thermal tail

Result0=400j =1°0=0.5°obs=0.3°

Comparison with Band function

β= -2.3α= -1

Structured jet model can reproduce Band function

α

β

-2.3

-1

Summary

Structured jet can natural produce a power-law non-thermal tail above the peak energy

-

- Band Spectrum can be reproduced

Futrure works

・ Evaluation of the polarization

・ Photon accelerations in various structures

・ Hydrodymical simulation of relativistic jet as a background fluid

multi-component, shocks, turbulence