本文章最後由 iheby 於 2015-11-19 09:34 編輯
以費米大視場望遠鏡對雙子座伽瑪射線源脈衝星之觀測 @港大物理系
Seminar - Fermi LAT(Large Area Telescope) Observations of the Geminga(Gemini Gamma-ray source) Pulsar
Pulsar is a kind of neutron star that emits a beam of electromagnetic radiation. When the beam of emission is pointing toward the earth, we can observe it. To explain the characteristic of pulsars, different pulsar models were developed, for example, the polar cap model, the outer gap model and TPC/slot gap model. The mainly differences between these models are the different acceleration regions for high-energy particles and relative emission mechanisms to radiate γ rays.
Fermi satellite was launched in 2008, since then it has collected many useful data for studying pulsars. By using the data collected by Fermi, we reanalyze the spectrum of geminga pulsar, and find the outer gap model is more suitable.
時間：2015.08.12(三) 10:00
地點：香港大學莊月明物理樓522室
講者：Miss Yating CHAI (The University of Hong Kong, Postgraduate Student)
脈衝星的伽瑪射線光譜特性：三維雙層外隙模型 @港大物理系
Seminar - Gamma-ray Spectral Properties of Pulsars: A Three-Dimensional Two-layer Outer Gap Model
Gamma ray pulsars have been long studied ever since their discovery. A two-layer outer gap model is now used to explain the high energy emission, spectral properties and light curves of pulsars. This model describes the outer gap as a region consists of two parts, the acceleration region and the screening region. In the accelerating region the the charge density is very low and the charged particles can be accelerated to relativistic velocity along the magnetic field and emit high energy photons and in the screening region the charge density is high and the gap is closed. A three-dimensional two-layer outer gap model with an azimuthal structure was previously proposed to explain the energy-dependent third peak of Vela pulsar by Fermi observation, which fitted well to the observation. This model is now being applied to other pulsars, compare their model phase-averaged spectrum, phase-resolved spectrum and light curves with the observations, and the results show that the spectra are well fitted either under the cutoff energy or above, but not in the entire energy band from 100MeV to 300GeV. It is suggested that a weighting factor should be assigned to one of the main parameters that indicates the size of the gaps, and a distribution can be given to such parameter, which improved the model fitting results. This is probably caused by the time-dependent structure of the outer gaps which is not considered in the current model, which is the next step of this research work.
時間：2015.08.12(三) 10:30
地點：香港大學莊月明物理樓522室
講者：Mr. Yuzhe SONG (The University of Hong Kong, Postgraduate Student)
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