报告一：Magnetic Field Configurations of Magentars

主讲人 (Speaker): Kotaro Fujisawa博士

主讲人单位 (Speaker's Institute): Waseda University

时间 (Time): 星期二, 2018/03/13，下午2：00-2：55

地点 (Location): 理学实验楼719

摘要 (Abstract):

　　Neutron stars have the strongest magnetic fields among stars in the Universe. In particular, Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters are considered to be magnetars, a special class of magnetized neutron stars. Magnetars have very strong dipole magnetic fields whose typical values reach approximately 10^15 G at their surfaces. They display stationary intense emissions and dynamical flares releasing magnetic energy. The magnetic field configurations of magnetars are important because the energy releasing process and magnetic field evolution depend on their magnetic field structures. In this study, we considered both core and crust of magnetars and calculated magnetic field configurations simultaneously. We found the interaction between core field and crustal field are important to consider magnetic field configurations of magnetars.

主讲人简介 (Speaker's CV):

　　2009: Bachelor, University of Tokyo 2011: Master, University of Tokyo 2014: Ph.D, University of Tokyo 2014-2016 : Junior Researcher, Waseda University 2016-present : JSPS fellow, Waseda University

报告二：Magnetar Giant Flares in Multipolar Magnetic Fields

主讲人 (Speaker): 黄磊博士

主讲人单位 (Speaker's Institute): 上海天文台

时间 (Time):  星期二, 2018/03/13，下午3：00-3：55

地点 (Location): 理学实验楼719

摘要 (Abstract):

　　We have analyzed the multipolar magnetic field structure variation at neutron star surface by means of the catastrophic eruption model and find that the variation of the geometry of multipolar fields on the magnetar surface could result in the catastrophic rearrangement of the magnetosphere, which provides certain physical mechanism for the outburst of giant flares. The magnetospheric model we adopted consists of two assumptions: (1) a helically twisted flux rope is suspended in an ideal force-free magnetosphere around the magnetar, and (2) a current sheet emerges during the flux rope evolution. Magnetic energy accumulates during the flux rope’s gradual evolution along with the variation of magnetar surface magnetic structure before the eruption. The two typical behaviors, either state transition or catastrophic escape, would take place once the flux rope loses equilibrium; thus, tremendous accumulated energy is radiated. We have investigated the equilibrium state of the flux rope and the energy release affected by different multipolar structures and find structures that could trigger violent eruption and provide the radiation approximately 0.5% of the total magnetic energy during the giant flare outburst. Our results provide certain multipolar structures of the neutron star’s magnetic field with an energy release percentage 0.42% in the state transition and 0.51% in the catastrophic escape case, which are sufficient for the previously reported energy release from SGR 1806–20 giant flares.

主讲人简介 (Speaker's CV):

　　1999 - 2003, B.S., Shanghai Jiaotong University 2003 - 2008, Ph.D., Shanghai Astronomical Observatory 2008 - 2010, Postdoc, University of Sciences and Technology 2011 - , Assoc.Researcher, Shanghai Astronomical Observatory