Numerical Study on GRB-Jet Formation in Collapsars

Two-dimensional magnetohydrodynamic simulations are performed using the ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB jet, taking account of realistic equation of state, neutrino cooling and heating processes, magnetic fields, and gravitational force from the central black hole and self gravity. It is found that neutrino heating processes are not so efficient to launch a jet in this study. It is also found that a jet is launched mainly by B_\phi fields that are amplified by the winding-up effect. However, since the ratio of total energy relative to the rest mass energy in the jet is not so high as several hundred, we conclude that the jets seen in this study are not be a GRB jet. This result suggests that general relativistic effects, which are not included in this study, will be important to generate a GRB jet. Also, the accretion disk with magnetic fields may still play an important role to launch a GRB jet, although a simulation for much longer physical time (\sim 10-100 s) is required to confirm this effect. It is shown that considerable amount of 56Ni is synthesized in the accretion disk. Thus there will be a possibility for the accretion disk to supply sufficient amount of 56Ni required to explain the luminosity of a hypernova. Also, it is shown that neutron-rich matter due to electron captures with high entropy per baryon is ejected along the polar axis. Moreover, it is found that the electron fraction becomes larger than 0.5 around the polar axis near the black hole by \nu_e capture at the region. Thus there will be a possibility that r-process and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons will be ejected from the jet, which suggests that signals from the neutron decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ. High resolution version is available at http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd

Outflow Propagation in Collapsars: Collimated Jets And Expanding Outflows

We investigate the outflow propagation in the collapsar in the context of gamma-ray bursts (GRBs) with 2D relativistic hydrodynamic simulations. We vary the specific internal energy and bulk Lorentz factor of the injected outflow from non-relativistic regime to relativistic one, fixing the power of the outflow to be 10{sup 51}erg s{sup -1}. We observed the collimated outflow, when the Lorentz factor of the injected outflow is roughly greater than 2. To the contrary, when the velocity of the injected outflow is slower, the expanding outflow is observed. The transition from collimated jet to expanding outflow continuously occurs by decreasing the injected velocity. Different features of the dynamics of the outflows would cause the difference between the GRBs and similar phenomena, such as, X-ray flashes

カキ樹の生理生態学的研究 III : 夜温が新梢生長, 開花ならびに果実肥大に及ぼす影響(農学部門)

カキの成木結果樹を供試し, それぞれ樹体の発育周期に応じて, 夜間に補温処理を行ない, 枝梢の生長, 開花ならびに果実の肥大に及ぼす影響を調査した。その結果, 新梢伸長期(自然夜温12∿13.4℃)および果実発育の第1期(自然夜温21∿22℃)に3∿4℃以内で夜間補温すれば, 新梢の生長, 開花および果実の肥大を促進し, とくにその期間中で処理を打ち切った後もその影響が維持されて収穫期にまでおよぶ。しかし, この時期に自然夜温より6∿7℃以上の高夜温になると, 一時的には展葉, 開花ならびに幼果の肥大は促されるが, 枝葉は軟弱徒長し開花後の落果が著しい。開花と萠芽時よりの積算夜温とは密接な関係を示し, 4月始めよりほぼ470℃∿500℃で開花期に至る。Some effects of night temperature on the shoot elongation, blooming and enlargement of fruit were studied by Confining fruiting limls during the night (7p.m-7a.m) in heated chambers. By the treatment at the shoot growth stage (the mean natural night temperature is 12-13.4℃ through treatment period) and the first stage of fruit growing (the mean natural night temperature is 21-22℃ throught treatmentp eriod), shoot elongation, blooming and fruit enlargement were much acceler ated, in case of 3∿4℃ above the natural night temperature, and this tendency was continued till harvest, even if the treatment discontinued merely at the first stage of fruit growing. However, when the treatment tremperature was 6∿7℃ higher than the natural night temperature, all young fruits fell down at about 10∿20 days after the treatment. The flowering is closely connected with the accumlatively night temperature before the flowering. In the treatment of 1959 and 1960,we observed that accumlatively night temperature from the beginning of April to flowering stage is 470-500