Rotating BHs as Central Engines of Long GRBs: Faster is Better

We performed simulations of collapsars with different Kerr parameters a=0, 0.5, 0.9, 0.95. It is shown that a more rapidly rotating black hole is driving a more energetic jet. No jet is seen for the case of Schwartzschild black hole case, while the total energy of the jet is as large as 10^50 erg for a rapidly rotating Kerr black hole case (a=0.95). In order to explain the high luminosity of a GRB, it is concluded that a rapidly rotating black hole is favored ('faster is better'). We also find in the case of a=0.95 that (i) the stagnation region is clearly found in the jet region, (ii) the ordered poloidal field lines are seen in the jet, (iii) the jet region is surrounded by a 'Wall-like' structure that has a higher pressure than the jet region and contains strong vertical magnetic fields, and (iv) the jet is initiated by outgoing Poynting flux from the outer horizon of the black hole (Blandford-Znajek effect). The bulk Lorentz factor of the jet is still of the order of unity. However, energy density of electro-magnetic fields dominates the one of rest-mass in the jet. It can be expected that a relativistic jet will be seen if we perform a simulation for a longer time scale (of the order of 10-100 sec).Comment: 8 pages, 7 figures, Publications of the Astronomical Society of Japan (PASJ), accepted (to be published on December 25th, 2011

Fermi-LAT study of two gamma-ray binaries, HESS J0632+057 and AGL J2241+4454

GeV gamma-ray emission from two gamma-ray binary candidates, HESS J0632+057 and AGL J2241+4454, which were recently reported by H.E.S.S. and AGILE, respectively, have been searched for using the Fermi-LAT archival dataset. Spatial and temporal distribution of gamma-ray events are studied, but there was no evidence for GeV gamma-ray signal from either sources.Comment: 2012 Fermi Symposium proceedings - eConf C12102

Effects of Magnetic Fields on Proto-Neutron Star Winds

We discuss effects of magnetic fields on proto-neutron star winds by performing numerical simulation. We assume that the atmosphere of proto-neutron star has a homogenous magnetic field (ranging from ~10^{12} G to ~10^{15} G) perpendicular to the radial direction and examine the dependence of the three key quantities (dynamical time scale, electron fraction, and entropy per baryon) for the successful r-process on the magnetic field strength. Our results show that even with a magneter-class field strength, ~10^{15} G, the feature of the wind dynamics varies only little from that of non-magnetic winds, and that the condition for successful r-process is not realized.Comment: submitted to Progress of Theoretical Physics. 28 pages, 13 figure