Title：Formation of a magnetically arrested disk (MAD) in a black hole x-ray binary

Speaker：Bei You(Wuhan University)

Special Time：3:00PM, Dec. 15 Friday

Tencent Meeting：576-157-8290  password: 6360

Location: Lecture Hall, 3rd floor

Report in Chinese

Abstract：

Accretion of material onto a black hole drags any magnetic fields present inwards, increasing their strength. Theory predicts that sufficiently strong magnetic fields can halt the accretion flow, producing a magnetically arrested disk (MAD). We analyze archival multi-wavelength observations of an outburst from the black hole X-ray binary MAXI J1820+070 in 2018. The radio and optical fluxes are delayed by about 8 and 17 days respectively, compared to the X-ray flux. We interpret this as evidence for the formation of a MAD. In this scenario, the magnetic field is amplified by an expanding corona, forming a MAD around the time of the radio peak. The optical delay is then due to thermal viscous instability in the outer disk.

CV：

游贝，武汉大学物理科学与技术学院副教授，2014年获得中国科学院上海天文台博士学位。2014-2017年在波兰科学院哥白尼天文中心开展博士后研究。2017年入职武汉大学，工作至今。长期从事黑洞吸积、喷流的研究，主要包括黑洞X射线双星爆发过程中能谱和时变的研究等。主持国家优秀青年科学基金和面上等项目，获得小米青年学者资助。以第一作者和通讯作者，在《Science》、《Nature Communications》等国际学术刊物发表学术论文，揭示了黑洞吸积和磁场输运的物理过程。