时间：10月20日上午10点

　　地点：报告厅406

　　报告人：Can Gungor

　　主持人：张澍 研究员

　　题目：Partial Accretion in the Propeller Stage of Low Mass X-ray Binary Aql X-1

　　摘要：

　　Aql X-1 is one of the most prolific low mass X-ray binary transients (LMXBTs) showing outbursts almost annually. We investigate the spectral changes related to the changing disk-magnetosphere interaction modes of Aql X-1. The X-ray light curves of the outbursts of LMXBTs typically show phases of fast rise and exponential decay. The decay phase shows a “knee” where the flux goes from the slow decay to the rapid decay stage. We assume that the rapid decay corresponds to a weak propeller stage at which a fraction of the inflowing matter in the disk accretes onto the star. We introduce a novel method for inferring, from the light curve, the fraction of the inflowing matter in the disk that accretes onto the NS depending on the fastness parameter. We determine the fastness parameter range within which the transition from the accretion to the partial propeller stage is realized. This fastness parameter range is a measure of the scale-height of the disk in units of the inner disk radius. We applied the method to a sample of outbursts of Aql X-1 with different maximum flux and duration times. We show that different outbursts with different maximum luminosity and duration follow a similar path in the parameter space of accreted/inflowing mass flux fraction versus fastness parameter.

　　个人简介：

　　Dr. Can Gungor has accepted Bachelor degree and master degree at Egean university. During his master, he has been in Catania observatory, Italy and researched on optical observation of low mass eclipsing binaries. He has the phd degree from Istanbul Technical University, Department of Physics Engineering and worked on Low Mass X-ray Binaries under supervision of Prof. Yavuz EKSI. During phd, he worked at Astronomy Department of Jena University, Germany under supervision of Prof. Ralph Neuhaeuser as visiting researcher for one year. Lastly, he worked as post doctor on the timing properties of magnetars at Sabanci University, Faculty of Natural Sciences under the supervision of Prof. Ersin GOGUS. And now he is working as post doctor under the supervision of Prof. Fangjun Lu.

　　Research Interests: Neutron Stars; Accreting Millisecond X-Ray Pulsars, Mass-Radius Relation, Equation of State, Accretion Disks, X-ray Observations. Low Mass Stars; Photometric and Spectral Observations, Mass-Radius Relation, Activity. Asteroids; Photometry of Asteroids.