I would like to present my recent study on collapsars using a General Relativistic MHD (GRMHD) code that I have developed. Also, I have developed a General Relativistic Force-Free (GRFFE) code by which Blandford-Znajek’s paraboloidal solution is reproduced. I am going to discuss how important it is to develop a hybrid code that includes GRMHD and GRFFE codes toward understanding the central engine of a long GRB. Further, I have done numerical simulations on collapsars using ZEUS code by adding some microphysics such as a realistic equation of state and neutrino cooling/heating (Nagataki et al. ApJ 2007). If I have enough time, I would like to talk about explosive nucleosynthesis in a collapsar (Nagataki et al. ApJ 2006), which can give a strict constraint on the central engine of a long GRB.
Yukawa Institute for Theoretical Physics, Kyoto University