中国科学院云南天文台学术报告通知

2025年第17期

报告题目：Observational approach to study the variability properties around black holes in the perspective of the TCAF model / Theoretical understanding of accretion flows around black holes

报告人：Kaushik Chatterjee (Postdoc) / Chandra Bahadur Singh (Associate Research Professor)

报告人单位：SWIFAR, Yunnan University（云南大学中国西南天文研究所）

报告语言：English

报告时间：6月25日（星期三）10:00-12:00

报告地点：3号楼1楼会议室

报告摘要1：

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In a black hole X-ray binary (BHXRB) system, or the case of active galactic nuclei (AGN), matter from the companion or the surrounding area is gravitationally attracted to the compact object. In the case of BHXRBs, when matter from the companion comes inside the sphere of gravitational influence of the compact object via Roche Lobe, it experiences some turbulent instability which also includes the magnetic field, if present. Due to this instability, matter gains enough viscosity (also known as critical viscosity) to start to come closer to the black hole (BH) by forming a spiral disk-like shape, called the thin disk. Since the angular momentum is conserved, this instability allows the transport of angular momentum to form a disk and come closer to the BH. This process is known as the process of accretion. During the accretion process, as matter gets much closer to the BH, some radiation comes out as the conversion takes place between the gravitational potential energy and kinetic energy. During accretion, matter can also be expelled from the system in the perpendicular direction to the disk, which is known as jets or outflows. Jets/outflows are highly energetic phenomena that are associated with both the stellar-mass black holes (SBHs). It is observed that accretion and ejection are connected and it was shown in the literature that the outflow depends on the inflow of matter or accretion. There are debates about the production of jets in both the SBH and AGN systems. During outbursts, the flux from the source increases to a scale of 100 to 1000 times and becomes detectable

to the observing facilities. Observable signatures, such as variabilities in light curves and the spectra are often seen during the onset of an outburst. These variabilities could be seen across the full electromagnetic wavelength. Timing variabilities in the accretion disks, such as the quasi-periodic oscillations (QPOs), are likely to be associated with shock instabilities in advective flows around the black holes. This shock instability can also produce a variable nature of the radiation in the form the spectral variability. In this presentation, we plan to show how the shock instability model can explain these variabilities by analyzing the spectro-temporal and outflow properties to address the possible physical scenario.

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报告人简介1： 

Kaushik Chatterjee. Ph.D. (2022, University of Calcutta / Indian Centre for Space Physics), Postdoc (2023-present, SWIFAR, Yunnan University).

报告摘要2：

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Black hole accretion is transonic in nature. Such flows around black holes can have range of angular momentum values. It is likely that the flows are required to be in cold and hot modes with different dynamical properties. In my talk, I will give overview of various aspects of accretion physics which can help us address the associated observational signatures. The main focus will be to highlight the semi-analytical and simulation techniques involved.

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报告人简介2： 

Chandra Bahadur Singh副研究员 (2020-), 云南大学中国西南天文研究所 SWIFAR、 以色列特拉维夫大学博士后(2017-2019)、巴西圣保罗大学博士后(2013-2017)、印度空间物理中心研究员(2008-2012)、印度贾达普大学物理学博士(2008-2013)、尼泊尔特里布万大学物理学硕士(2004-2007)、尼泊尔特里布万大学物理学学士(2001-2004)。 研究领域：利用半解析和数值的方法回答物质如何回落进黑洞并产生宇宙中能量最高的外流（高能天体物理、黑洞吸积和抛射现象、相对论流体动力学）。

云台邀请团组：星系类星体研究团组

邀请方联系人：毛基荣