Monte-Carlo Simulation of Thermal Radiation from GRB Jets Sanshiro Shibata (Konan Univ.) Collaborator: Nozomu Tominaga (Konan Univ., IPMU) Introduction Models for the prompt emission • Internal shock model – A standard scenario for a long time. – Low Radiative efficiency, line of death problem • Photospheric (thermal emission) model – Thermal emission from relativistic jets – (possibly) high radiative efficiency – Some GRBs exhibit blackbody like feature (e.g., GRB090902B). (Ryde et al 2010) Thermal emission from GRB jets • Thermal emission from GRB jets have been investigated by performing hydrodynamical simulations. (Lazzati+2009, Mizuta+11, Nagakura+11) • They calculated the light curves and spectra by superposing blackbody radiation emitted from the photosphere with τ=1. progenitor jet photon photosphere observer Thermal emission from GRB jets However – The observed photons may be generated in the inner layer with τ > 1 (e.g., εfree-free∝n2). – Radiation intensity can be anisotropic even in the comoving frame at τ～1. (Beloborodov 2011) In order to treat the thermal radiation from GRB jets properly, both the radiative transfer in the jet and complex structure of the jet and cocoon should be taken into account. We calculate the radiative transfer in the jet. Method Hydrodynamical simulation 2D relativistic hydrodynamics (Tominaga 2009) Setup – Progenitor: 14Msun WR star (Rstar～1.5×1010cm) – Γ0=5 – Θjet=10° θjet – Ljet=5.3×1050 erg s-1 – fth=0.9925 (eint/ρc2=80) Ljet, fth, Γ0 – (log r, θ) = (600, 150) grids R0 from R0=109cm Rstar Hydrodynamical simulation Density [g/cc] Radiative transfer Numerical code observer progenitor – Monte Carlo method – Calculate Compton scattering – Photons are injected at τ= τinj jet photon τinj photosphere Photon injection – 4 models with τinj =1, 5, 7, 10 – Planck distribution with local plasma temperatures τinj=1 =10 – Isotropic in the comoving frame τinj We use a snapshot at t=40s as the jet and cocoon structure. τ=1 τ=10 Results Energy spectra • Epeak is higher for τinj=5 than for τinj=1. • The models with τinj=10 have wide shape. Black Body Energy spectra of τinj=10 • Photons with large number of scatterings are tend to have lower energies. The spectrum becomes wide. Comparison to observations α=0 Black Body (Kaneko et al. 2006) Summary Summary We develop a numerical code to calculate radiative transfer in the relativistic jet. We perform radiative transfer calculation in relativistic jet and cocoon with complicated structure, which is obtained by 2D relativistic hydrodynamical calculation. The emergent spectra with different τinj have different properties; e.g., Epeak and peak width. We should treat the radiative transfer in the jet properly in order to constrain the GRB prompt emission models.