Photospheric emission from Structured Jet Hirotaka Ito Collaborators Shigehiro Nagataki YITP ＠ YITP Lunch Seminar /30 Shoichi Yamada Waseda University

Gamma-Ray Burst (GRB) ・ duration T ~ 10ms ー 100s ・ rapid variability δt ～ ms Most luminous explosion in the universe L γ,iso ~ erg/s Time (s) Counts/s ・ event rate ~1000/yr

Briggs ~ -0.9 β~ -2.5 ν ν^(-0.5) Band function ~ 160 keV ~ 490 keV Long GRB Short GRB α~ -1 ~ -0.5 ~ -2.3 Nava F ν ∝ ν -α （ hν< E p ） F ν ∝ ν -β （ hν> E p ） Prompt Emission Spectrum

Model for Emission Mechanism Internal Shock Model Photospheric Emission Model photosphereInternal shock External shock γ γ ・ Low efficiency for gamma-ray production ・ too hard spectrum in low energy band (α) GRB090902B Ryde et al (2009) (e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007) flaw

photosphereInternal shock External 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 Photosphere Accleration region We solve the propagation of photons within the spine sheath jet  0 >  1 Present Study Photon acceleration in a structured jet as a mechanism for production of non-thermal tail Spine-Sheath jet

r Spine (θ<θ 0 ) Sheath (θ 0 <θ<θ j ) Calculation Range r in << R ph r out = 500R ph (τ~2×10 -3 ) r in (τ>>1) r out (τ<<1) Model :photospheric radius Velocity Spine-Sheath Electron number density

r Spine (θ<θ 0 ) Sheath (θ 0 <θ<θ j ) Initial Condition Inject thermal photons at the inner boundary r in (τ>>1) r out (τ<<1) Model L in = 5.4×10 52 r 8 2/3  400 8/3 L 53 1/3 (r in /10 11 cm) -2/3 erg/s T in = 0.9 r 8 1/6  400 8/3 L 53 -5/12 (r in /10 11 cm) -2/3 keV Propagation of photons are solved by Monte=Carlo method Velocity Spine-Sheath Electron number density

E max =  0 m e c 2 Klein-Nishina cut-off Spine Sheath Thermal + non-thermal tail Result  0 =400  j =1°  0 =0.5°  obs =0.3°

Comparison with Band function β= -2.3 α= -1 Structured jet model can reproduce Band function α β -2.3

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