UFFO UBAT 焦平面元件之校正與改良

Abstract

UFFO (Ultra-Fast Flash Observatory)是一個由衛星搭載，以觀測GRBs (Gamma-Ray Bursts)為目標的探測器。拜MEMS (Micro-Electronic-Mechanical-System)科技所賜，UFFO是史上第一個可在一分鐘內啟動可見光(即afterglow)頻段觀測的GRB探測器。這可貴的早期afterglow將有助於我們推展對於Dark Bursts、Short-Hard Bursts(SHBs)和超新星的了解。 UBAT (UFFO Burst Alert and Trigger Telescope)是 UFFO 中的X-ray/Gamma-ray望遠鏡，負責決定GRB事件的方向並交由光學望遠鏡 SMT (Slewing-Mirror Telescope)做瞄準之用。由於 UBAT 是以coded mask aperture camera方法決定事件方向，編碼遮罩(coded mask)在焦平面上的成像品質直接決定了計算方向的精確度，以及 SMT 接續瞄準的成功率。 UBAT 焦平面元件包含了36對的64通道MAPMT和YSO (Yttrium Oxyorthosilicate)閃爍體陣列的組合，稱為焦平面的觀測單元(detection unit)。本研究的目標即是焦正並改良觀測單元的性能。 在此論文中，我在第一章首先回顧了GRB物理，並特將與 UFFO 實驗相關的部分獨立於最後一節討論之。第二章介紹了 UFFO 實驗的硬體設計，包含整合運作與實驗計畫，以及 UBAT 及 SMT 的分項探討。在第三章中我說明了本研究的實驗設計，接著在第四章說明了各實驗儀器的性能與校正方法和結果。第五章分析了未改良前的觀測單元的校正結果，內容以其訊號強度以及成像解析度為關注焦點。根據第五章所呈現的初步結果，我建構了 UBAT 的蒙地卡羅電腦模擬模型。根據電腦模擬的結果，我提出了對於模糊成像的解釋。所有關於模擬的研究討論，從建構、 執行到數據分析，都包含在第六章中。綜合以上，我得以提出反錐形光導(Inverted-Conical Light Guide, ICLG)作為可行的改良方法。我在第七章中詳細介紹了ICLG的發想，設計，以及電腦模擬最佳化過程。最後，我製作了一個ICLG樣本並安裝於觀測單元。關於樣本的製作，以及安裝ICLG後觀測單元的性能都在第八章中詳細介紹。

UFFO (Ultra-Fast Flash Observatory) is a space-borne observatory aims to observe GRBs (Gamma-Ray Bursts) in X-ray and soft Gamma-ray. Thanks to the innovative MEMS (Micro-Electronic-Mechanical-System) technology, UFFO is built to be the first observatory ever capable to respond to GRBs within a minute in the optical range, i.e. afterglows. Through the observation of the sub-minute afterglows, UFFO will hopefully provide new perspectives to our understand toward the natures of Dark Bursts, Short-Hard Bursts (SHBs), Type-1A Supernovae, and other exciting new physics. UBAT (UFFO Burst Alert and Trigger Telescope) is the primary telescope in UFFO responsible for the X-ray/gamma-ray detection, event direction decision and the triggering of optical telescope SMT (Slewing-Mirror Telescope). Since UBAT determines the directions of GRBs in the coded mask aperture camera scheme, the coded mask image resolvability on the focal surface (FS) is crucial to the successiveness of the entire operation. The UBAT FS includes 36 assemblies of YSO (Yttrium Oxyorthosilicate) scintillator arrays and 64-pixels MAPMTs (Multi-Anode Photon Multiplier Tubes). The main focus of this thesis is the calibration and the amelioration of the UBAT FS detection assemblies. As to begin, I give a general review on GRB physics in chapter 1 with the perspective physics of UFFO emphasized in the last section. The design of UFFO observatory is introduced in chapter 2, breaking into the UBAT, SMT sections, and a separated section dedicated to UBAT FS. Chapter 3 explains the experimental design and the expected result. The instrument calibration of UBAT MAPMT is reported in chapter 4. The calibrations of UBAT FS energy scale and image resolvability is elaborated in chapter 5. The result failed to match the designed performance of UBAT. A specialized simulation package was then developed to further investigate the cause. The construction and indication of the simulation are discussed in chapter 6. I propose the Inverted-Conical Light guide (IC-LG) based on the simulation study in chapter 7 as a possible amelioration to UBAT FS. Chapter 8 summaries all the works achieved in this thesis and gives the conclusion.