Photospheric emission from Structured Jet Hirotaka Ito Collaborators Shigehiro Nagataki YITP Shoichi Yamada Waseda University ＠YITP Lunch Seminar 2012 5/30 Gamma-Ray Burst (GRB) Most luminous explosion in the universe Lγ,iso ~ 1052 erg/s ・event rate ・duration T ~ 10ms ー 100s Counts/s ~1000/yr ・rapid variability δt ～ ms Time (s) Prompt Emission Spectrum Band function α~ -1 β~ -2.5 Fν∝ν-α （hν< Ep） Fν∝ν-β （hν> Ep） Long GRB < Ep > ~ 160 keV ν ν^(-0.5) <α>~ -0.9 Short GRB < Ep > ~ 490 keV <α>~ -0.5 <β>~ -2.3 Briggs + 1999 Nava + 2011 Model for Emission Mechanism Internal Shock Model flaw ・Low efficiency for gamma-ray production ・too hard spectrum in low energy band (α) Photospheric Emission Model (e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007) γ photosphere γ Internal shock External shock Model for Emission Mechanism Internal Shock Model flaw ・Low efficiency for gamma-ray production ・too hard spectrum in low energy band (α) Photospheric Emission Model flaw: high energy non-thermal tail（β） 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) γ photosphere γ Internal shock External shock Present Study Photon acceleration in a structured jet as a mechanism for production of non-thermal tail Spine-Sheath jet G0 > G1 Photosphere τ~1 G0 >> 1 Spine Sheath G1 >> 1 Present Study Photon acceleration in a structured jet as a mechanism for production of non-thermal tail Spine-Sheath jet G0 > G1 Photosphere Accleration region G0 >> 1 Spine τ~1 Photons gain energy by crossing the boundary layer Sheath G1 >> 1 We solve the propagation of photons within the spine sheath jet Model Spine (θ<θ0 ) Sheath (θ0<θ<θj ) Velocity Spine-Sheath rout (τ<<1) Electron number density rin (τ>>1) Calculation Range rin << Rph r rout = 500Rph(τ~2×10-3) :photospheric radius Model Spine (θ<θ0 ) rout (τ<<1) Sheath (θ0<θ<θj ) Velocity Spine-Sheath Electron number density rin (τ>>1) Initial Condition Inject thermal photons at the inner boundary r Tin = 0.9 r81/6G4008/3 L53-5/12 (rin/1011cm)-2/3 keV Lin = 5.4×1052 r82/3G4008/3 L531/3 (rin/1011cm)-2/3 erg/s Propagation of photons are solved by Monte=Carlo method Result G0=400 qj =1° q0=0.5° qobs=0.3° Thermal + non-thermal tail Spine Sheath Emax = G0mec2 Klein-Nishina cut-off Comparison with Band function -1 α= -1 β= -2.3 α -2.3 β Structured jet model can reproduce Band function Summary - Structured jet can natural produce a power-law nonthermal tail above the peak energy Band Spectrum can be reproduced Futrure works ・Photon accelerations in various structures multi-component, shocks, turbulence ・Evaluation of the polarization ・Hydrodymical simulation of relativistic jet as a background fluid
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