本文章最後由 iheby 於 2016-4-11 15:55 編輯
伽瑪射線暴及其當刻發射光譜的銳利度 @香港大學物理學系
Seminar:- Gamma-ray Bursts and the Sharpness of their Prompt Emission Spectra
Gamma-ray bursts (GRBs) are the most violent explosion of massive stars in the universe discovered in 1967. Today, we still do not fully understand the emission mechanism of their prompt emission phase observed in gamma-ray energies. The idea of using synchrotron radiation from electrons to explain the observed GRB spectra is simple but problematic. In this study, we obtain 1,491 time-resolved spectra from the Fermi Gamma-ray Burst Monitor (Fermi GBM) and compute a move quantity - the sharpness angle - around the spectral peaks or breaks. We compare the observed values to the values measured from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. We conclude that more than 90% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model. We found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58(+23/-18)% of the observed peak flux. Our results also show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.
時間：2016.03.18(五) 11:00
地點：香港大學 莊月明物理樓 522室
講者：Dr. Hoi Fung David YU 余海峯 博士 (Max Planck Institute for Extraterrestrial Physics)
語言：英語
免費會議，歡迎公眾參加
【講者】
【圖片】wordpress.com > 淺談伽瑪射線暴
以高分辨率光譜學檢視系外巨大行星的大氣 @香港大學物理學系
Seminar:- Inspecting the Atmospheres of Giant Exoplanets with High-Resolution Spectroscopy
Over the past 20 years, more than 2000 planets beyond our Solar system have been found. Despite the large number of planets found, we have still little knowledge about their atmospheres. In the talk, the speaker will introduce the most robust method to date to measure molecular features and their properties in the exoplanet atmospheres: high-resolution spectroscopy at near-infrared wavelengths. In his research, the speaker focus on the exotic atmospheres of hot Jupiters, i.e. giant planets which are a few stellar radii away from their host stars. We can learn a lot from these studies, as the composition and structure of the atmospheres surrounding these planets provide a fossil record of their primordial origins. Their chemical composition can be directly linked to where and how the planet formed in its protoplanetary disk.
時間：2016.04.01(五) 16:30
地點：香港大學 莊月明物理樓 522室
講者：Dr. Florian RODLER (Max Planck Institute for Astronomy)
語言：英語
免費會議，歡迎公眾參加
【講者】
【圖片】nasa.org > The presence of methane in the atmosphere of extrasolar planet 189733b is measured by the Hubble Space Telescope
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