APゼミ　2020年度

1/25: 杉村 和幸（メリーランド大学）
初代銀河形成シミュレーション

アブストラクト:
ビッグバン後の宇宙進化において、最初の世代の星（初代星）の次に最初の世代の銀河（初代銀河）が形成し、現在に至るまでの銀河形成・進化史へとつながっていくと考えられている。本セミナーでは、まず、初代銀河形成過程において重要になるいくつかの物理過程について考察し、その後、自身が現在進めている初代銀河形成シミュレーションの現状について紹介する。

12/21: 木坂 将大 (広島大学)
ブラックホール磁気圏での電磁カスケード

アブストラクト:
　相対論的ジェットの根元に当たるブラックホールのホライズン近傍の磁気圏への物質の供給は, ジェットがどう加速してどう放射するかに直接影響するものの, 現在未解明である. 降着率が低い場合に対する有力な物質供給機構として, ホライズン近傍での電磁カスケードが挙げられる. この機構では, 磁気圏の強い電場で荷電粒子が加速され, 高エネルギーのガンマ線を放出し, このガンマ線を起点とした電子陽電子の雪崩的な生成で物質が供給される. このような過程は電磁流体シミュレーションでは一般には扱えない. 　本研究では, プラズマ粒子シミュレーションを行うことでブラックホール磁気圏での電磁カスケード現象の理論的な解明を目指す. 初期条件の影響が十分無視できる長時間計算を行なった結果, 効率の高い粒子加速と生成がある決まった領域で準周期的に起こることがわかった. また, 本研究では現実的な範囲のパラメータを採用した結果, 曲率放射が結果に与える影響, 具体的には曲率放射のガンマ線起源の粒子生成が電磁場構造に支配的な影響を与える条件, ガンマ線観測で検出されうる条件を明らかにした.

参考文献：
-Kisaka, Levinson & Toma (2020) ApJ 902 80

11/30 : 平井 遼介 (Monash 大学)
大質量多重連星内における様々な現象

アブストラクト:
The majority of massive stars are in binary systems, and understanding its evolution has become one of the hottest topics in astrophysics over the last few years. Some phases of its evolution are highly complex due to its multidimensional and hydrodynamical nature. Multidimensional hydrodynamical simulations can greatly help us understand such processes. Here I will present results of hydrodynamical simulations of various processes in massive binary systems. First I will discuss the interaction of supernova ejecta with a massive companion in close binaries and its diverse implications. I will particularly focus on applications to known supernovae such as SN2006jc and Cassiopeia A. Secondly I will discuss the formation of an extraordinary star, Eta Carinae. In our scenario Eta Carinae used to be a triple system of three massive stars and eventually caused a stellar merger that was observed as the Great Eruption in 1844. We were able to replicate many observed features of Eta Carinae with the combination of hydrodynamical and n-body simulations. Understanding the formation and evolution of Eta Carinae may help us understand the nature of other luminous blue variables, supernova impostors, or superluminous supernovae.

参考文献:
-Hirai et al. 2020 MNRAS, 499, 1,1154
-Hirai et al. arXiv:2011.12434

11/9 : 高棹 真介 （大阪大学)
原始星降着の円盤最内縁に関する磁気流体現象の研究

アブストラクト:
原始星は星周円盤から質量を獲得し成長するが、原始星進化過程は降着率だけでなく降着構造にも依存する。降着構造は磁場によって変わるため、磁場の影響を評価することは原始星進化の理解に重要である。さらに中心領域に溜め込まれた磁場は激しい爆発を駆動し、周囲の低温ガス、つまりは大スケールの降着ガスにも影響を及ぼす。我々は原始星や星周円盤の進化過程を理解することを目指し、いわば円盤の内側境界条件を決定するべく研究を進めてきた。本発表では原始星近傍や星表面の磁気流体過程に関する我々の研究を紹介し、他の降着系との関連についても議論する。

参考文献:
-Takasao et al. 2018 ApJ
-Takasao et al. 2019 ApJL
-Takasao et al. 2020 ApJ

10/19 : 細川 隆史
円盤分裂

参考文献:
-A revised condition for self-gravitational fragmentation of protoplanetary disks
Takahashi, S.Z., Ysukamoto, Y., & Inutsuka, S., (2016), MNRAS, 458, 3597
-Spiral-arm instability - III. Fragmentation of primordial protostellar discs
Inoue, S., & Yoshida, N., (2020), MNRAS, 491, L24

10/12 : Kohei Inayoshi (KIAA in Peking University)
Title : The Assembly of the First Massive Black Holes

Abstract :
The existence of ~10^9 Msun supermassive black holes (SMBHs) within the first billion year of the universe has stimulated numerous ideas for the prompt formation and rapid growth of BHs in the early universe. I will review ways in which the seeds of massive BHs may have first assembled, how they may have subsequently grown as massive as ~10^9 Msun. The following topics are mainly addressed: (1) formation of seed BHs in protogalaxies, depending on the environment (such as the number and properties of nearby radiation sources and the local baryonic streaming velocity), and on the metal enrichment and assembly history of the host galaxy. (2) rapid formation and growth of massive seeds via gas accretion in larger, metal-poor galaxies.

References :
-Inayoshi, Visbal & Haiman (2020), ARAA, 58 (arXiv:1911.05791)

10/5 : Hiroki Nagakura (Princeton Univ.)
Title:Recent progress in our understanding of core-collapse supernova

abstract:
Core-collapse supernova (CCSN) explosion is a fiery death of massive stars. The explosion mechanism seems to involves complex interplay between micro- and macroscopic physics, and its detail is still uncertain. Numerical simulations have been used in an effort to understand the roles of each physics, and they have made a remarkable progress with increasing computational resources in the last several years. In this seminar, I will introduce the current status of the community by presenting our recent results of multi-dimensional numerical modeling of CCSN made by 2D/3D full Boltzmann simulations (in collaboration with a Japanese group) and another 3D simulations (in Princeton group). Based on the result of the former project, I will mainly discuss roles of asymmetric neutrino emissions on the origin of neutron star kick and on collective neutrino oscillations. For the latter, I will discuss the progenitor dependence of explodability, proto-neutron star convection and neutrino signals based on the results of systematic 3D simulations. If time allows, I will also present some preliminary results of currently on-going our studies; non-thermal neutrinos from CCSN and its observational consequence; how we will efficiently use observed data on multiple detectors (e.g., SuperKamiokande/HyperKamiokande and DUNE) to reconstruct neutrino spectra at a CCSN source.

7/29 : 諏訪雄大
共通外層の局所計算

参考文献:
-MacLeod et al. 2015
-MacLeod et al. 2015
-MacLeod et at. 2017
-De et al. 2020

7/22 : 島 和宏
What physics determines the peak of the IMF? Insights from the structure of cores in radiation-magnetohydrodynamic simulations

参考文献:
-Krumholz, et al., 2016, MNRAS, 460, 3272
-Gennaro & Robberto, 2020, ApJ, 896, 80
-Offner et al., 2014, prpl.conf, 53

7/15:石崎渉
Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants

参考文献:
- Gabici, S., Aharonian, F. A., & Casanova, S. 2009, MNRAS, 396, 1629
-Gabici, S., & Aharonian, F. A. 2007, ApJ, 665, L131
-Ptuskin V. S., Zirakashvili V. N., 2005, A&A, 429, 755

7/8:松岡知紀
Wind-reprocessed Transients

参考文献:
-Piro & Lu (2020), https://arxiv.org/abs/2001.08870
-Moriya, Mazzali, & Pian (2020), https://arxiv.org/abs/1911.01740
-Uno & Maeda (2020), https://arxiv.org/abs/2003.05795

7/1:高橋 卓弥
Searching for General Binary Inspirals with Gravitational Waves

参考文献:
-arXiv:2004.06729

6/24:間仁田侑典
もしPlanet9がPBHだったら観測できるのか？

参考文献:
-J. Scholtz and J. Unwin, “What if Planet 9 Is A Primordial Black Hole?” arXiv:1909.11090.
-Edward Witten, “Searching for a Black Hole in the Outer Solar System” arXiv:2004.14192.
-S. Lawrence and Z. Rogoszinski, “The Brute-Force Search for Planet Nine” arXiv:2004.14980.
-T. Hoang and A. Loeb, “Can Planet Nine Be Detected Gravitationally by a Sub-Relativistic Spacecraft?” arXiv:2005.01120
など

6/17 :林　航大
Velocity of the ejecta produced in BHNS merger

参考文献:
-K. Kyutoku et al., Phys. Rev. D 92, 044028 (2015)
-K. Kawaguchi et al., The Astrophysical Journal, Volume 825, Issue 1, article id. 52, pp. (2016)
-R. Ruffini and J. A. Wheeler, ESRO 52, 45 (1971).
-F. Foucart, Phys. Rev. D 86, 124007 (2012)

6/10 :久徳 浩太郎
連星ブラックホールの歳差運動

参考文献:
-Apostolatos et al. PRD 49, 6274-6297 (1994)
-Schnittman PRD 70, 124020 (2004)
-Gerosa et al. PRD 92, 064016 (2015)

6/3 : 井岡邦仁
Fast Radio Burst 200428 from the Galactic Magnetar SGR 1935+2154

参考文献:
-arxiv 2005.10324
-arxiv 2005.10828
-arxiv 2005.11178
-arxiv 2005.11071
-arxiv 2005.12164
-arxiv 2005.11479

5/20 : 和田知己
induced scattering of short radio pulses

参考文献:
- Lyutikov 2008
- Thompson et al 1994, ApJ, 422, 304

4/22 : 宇野真生
Periodic fast radio burst with NS precession

参考文献:
- Zanazzi, Lai 2020

4/15 : 木村和貴
The Evaporation Valley in the Kepler Planet

参考文献:
- Owen, Wu 2017