[日時] 毎週月曜日15時から / [Date] Monday 15:00-
[場所] 青葉サイエンスホールまたは合同A棟203 / [Venue] Aoba Science Hall or 203 Science Complex A
会場確保の都合上時間が変更になる場合があります。
No | Date and Time (YYYY/MM/DD, HH:MM-) |
Venue | Speaker | Title |
---|---|---|---|---|
1760 | 2024/04/08, 15:00- | Aoba Science Hall | 野田 博文(東北大学) | X-ray Observations and Detector Developments to Study the AGN Central Engine |
1761 | 2024/04/15, 15:00- | Aoba Science Hall | 石崎 渉(東北大学) | Fallback Accretion in Binary Neutron Star Mergers |
1762 | 2024/04/16, 15:00- | Aoba Science Hall | Ue-Li Pen(ASIAA) | FRBs: what are they and what are they good for? |
1763 | 2024/04/22, 15:00- | 203 Science Complex A | Ronaldo LAISHRAM(東北大学) | Cosmic Evolution and Environmental Dependence of Star Forming Activities and Morphologies |
1764 | 2024/05/13, 15:00- | Aoba Science Hall | 安部 大晟(東北大学) | |
1765 | 2024/05/17, 15:00- | TBA | Jeong-Gyu Kim(NAOJ) | |
1766 | 2024/05/20, 15:00- | Aoba Science Hall | Hefan Li(東北大学) | |
1767 | 2024/05/27, 15:00- | Aoba Science Hall | 和田 知己(東北大学) | |
1768 | 2024/05/31, 15:00- | TBA | Juan Pablo Alfonzo(東北大学) | |
1769 | 2024/06/10, 15:00- | Aoba Science Hall | 鈴木 竜二(NAOJ) | |
1770 | 2024/06/11, 15:00- | 203 Science Complex A | Evan Kirby(Notre Dame) | |
1771 | 2024/06/12, 15:00- | 203 Science Complex A | Benedetta Vulcani(INAF) | |
1772 | 2024/06/17, 15:00- | 203 Science Complex A | 北島 歓大(名古屋大学) | |
1773 | 2024/06/24, 15:00- | 203 Science Complex A | 藤林 翔(東北大学) | |
1774 | 2024/07/01, 15:00- | Aoba Science Hall | 鳥羽 儀樹(NAOJ) | |
1775 | 2024/07/08, 15:00- | Aoba Science Hall | 鈴木 昭宏(東京大学) | |
1776 | 2024/07/18, 15:00- | TBA | 藤本征史(University of Texas, Austin) | Quest for the Most Distant Universe |
1777 | 2024/07/22, 15:00- | 203 Science Complex A | TBA | |
1778 | 2024/07/29, 15:00- | 203 Science Complex A | TBA | TBA |
1760
2024/04/08 (Mon)
野田 博文(東北大学)
X-ray Observations and Detector Developments to Study the AGN Central Engine
The central engine which consists of an X-ray corona and accretion disk in the vicinity of a supermassive black hole is the origin of powerful radiation from an Active Galactic Nucleus (AGN). However, even its fundamental properties, such as its accretion state, geometric structure, and how these change with varying mass accretion rates have not yet been well understood. To establish the picture of the AGN central engine, we have performed X-ray and multi-wavelength observations of highly variable sources including changing-look AGNs which change their types in short timescales and are under much debate. In parallel, we have developed X-ray detectors onboard Japanese X-ray astronomical satellites, Hitomi and XRISM, to realize unprecedented X-ray spectral resolution for AGN studies. In this presentation, I introduce our observational studies, detector development, and prospects with XRISM for understanding the AGN central engine.
1761
2024/04/15 (Mon)
石崎 渉(東北大学)
Fallback Accretion in Binary Neutron Star Mergers
The gravitational wave event GW170817 with a kilonova shows that a merger of two neutron stars ejects matter with radioactivity including r-process nucleosynthesis. A part of the ejecta inevitably falls back to the central object, possibly powering long-lasting activities of a short gamma-ray burst (sGRB). We investigate the fallback accretion with the r-process heating by performing 1D hydrodynamic simulations and developing a semi-analytical model. We show that the fallback is halted by the heating. The characteristic halting timescale is 104-8 sec for the GW170817-like r-process heating, which is long enough to continue the long-lasting emission of sGRBs.
Furthermore, I will present a new interpretation of the recently reported re-brightening in the annual-scale X-ray light curve of GW170817. We model the fallback of the merger ejecta and construct a simple light curve model from the accreting ejecta. We find that the X-ray flux excess can be well explained by the fallback of the post-merger ejecta rather than the dynamical ejecta.
If time allows, I would like to introduce a study on the decay of Alfven waves in strongly magnetized plasmas. This process is relevant not only to binary neutron star mergers but also to the general problem in high-energy astrophysics in the context of the conversion of electromagnetic field energy into matter energy.
1762
2024/04/16 (Tue)
Ue-Li Pen(ASIAA)
FRBs: what are they and what are they good for?
Fast Radio Bursts are short, millisecond flashes thousands of times per day, distributed isotropically on the sky. I outline our current state of understanding for their nature and environment and their unique properties of cosmic probes. I describe the new BURSTT FRB initiative for ambitious instantaneous fish-eye coverage with VLBI localization across Asia, including Ogasawara and India.
1763
2024/04/22 (Mon)
Ronaldo LAISHRAM(東北大学)
Cosmic Evolution and Environmental Dependence of Star Forming Activities and Morphologies
The distribution of galaxies in the universe is inhomogeneous, representing large-scale structures (LSS) that consist of galaxy clusters, groups, and the filaments that connect them. Understanding how galaxy characteristics are influenced by their environments and how they evolve over cosmic time within LSS is crucial. Utilizing dual narrow-band filters for precise redshift estimation, we investigate the environmental effects on star formation within large-scale structures. We explore star-forming activity and the spatial distribution of Hα and continuum emission at z=0.4, probing the cosmic web. We found that star formation in cluster core galaxies is more centrally concentrated and reduced compared to the field sample, which may imply the influence of ram-pressure stripping. We also explore the morphological features and star formation activities of [OII] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. Furthermore, we report the discovery of large filamentary structures traced by [OII] emitters, surrounding an extremely overdense core with a galaxy number density ∼ 11× higher than the field average. Heightened star-forming activity was observed in dense regions, contrary to z=0.4, suggesting an environmental impact on early galaxy evolution. Additionally, we examine the redshift evolution of star-forming activities and morphology. Future studies will explore into the chemical abundance, gas content, and kinematics to comprehend the underlying processes.
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