水村 好貴

JAXA operates scientific balloon campaigns, aiming at obtaining scientific results through safe and reliable balloon flights. The development of the prototype of the flight prediction and control system began more than 20 years ago. It has become a mature system through many years of operation and functional enhancement and modification. The main functions of the system are implemented by a database system, which has been used for at least 82 heavy balloon experiments and 102 light balloon experiments since 2007. The applications used in client computers include more than 180 graphical user interface panels. The system is designed to incorporate redundancy for availability during balloon flight operations. Although various constraints face balloon flights, such as scientific requirements, flight safety, and severe high-altitude wind conditions, the flight prediction and control system enable us to construct a detailed flight plan and to control the flight based on predictions. In addition to the report of the system, flight prediction is explained with an example of boomerang flight control planning.

MeV gamma-rays provide a unique window for the direct measurement of line emissions from radioisotopes, but observations have made little significant progress since COMPTEL on board the Compton Gamma-ray Observatory (CGRO). To observe celestial objects in this band, we are developing an electron-tracking Compton camera (ETCC) that realizes both bijective imaging spectroscopy and efficient background reduction gleaned from the recoil-electron track information. The energy spectrum of the observation target can then be obtained by a simple ON–OFF method using a correctly defined point-spread function on the celestial sphere. The performance of celestial object observations was validated on the second balloon SMILE-2+ , on which an ETCC with a gaseous electron tracker was installed that had a volume of 30 × 30 × 30 cm³. Gamma-rays from the Crab Nebula were detected with a significance of 4.0σ in the energy range 0.15–2.1 MeV with a live time of 5.1 hr, as expected before launch. Additionally, the light curve clarified an enhancement of gamma-ray events generated in the Galactic center region, indicating that a significant proportion of the final remaining events are cosmic gamma-rays. Independently, the observed intensity and time variation were consistent with the prelaunch estimates except in the Galactic center region. The estimates were based on the total background of extragalactic diffuse, atmospheric, and instrumental gamma-rays after accounting for the variations in the atmospheric depth and rigidity during the level flight. The Crab results and light curve strongly support our understanding of both the detection sensitivity and the background in real observations. This work promises significant advances in MeV gamma-ray astronomy.

将来の大型高精度構造物の実現のために，著者らは高精度変位計測装置の研究開発を行っている．特に，X 線望遠鏡の支持構造など，1 次元的に細長い構造の両端の相対位置の計測に焦点を当てている．変位計測装置は，レーザ光源，ビームスプリッタ，レトロリフレクタ，PSD(Position Sensitive Device)からなる．レーザ光源とレトロリフレクタは，相対位置を計測する基準とターゲットに取り付けられる．開発中の変位計測装置は，実利用に先んじて，大型天文衛星の地上試験に使用され，その有用性が確かめられた．宇宙や成層圏での天文観測において実際に使用するためには，それぞれの環境での適合性を確認する必要がある．そこで，大気球実験における天文観測機器での利用を想定し，成層圏環境での機能実証を試みた．2021 年7 月9 日に，大気球実験：DREAM（DemonstRation Experiment of Alignment Monitor）を実施した．最高高度は29 ㎞，フライト時間は2時間54分であった．気球ゴンドラのサイズ制約から，レーザ光源とレトロリフレクタ間の距離は1mとした．気球実験を通じて，成層圏の気球実験環境下において本変位計測装置が正常に機能することが確かめられた．実験においては，上空で計測対象（レトロリフレクタ）に所定の変位を与えるために，人工的な周期的熱膨張を発生させた．計測された温度から推定された変位と，変位計測装置によって計測された変位の差は0.4μmRMS であった．

<title>Abstract</title> The Electron-Tracking Compton Camera (ETCC), which is a complete Compton camera that tracks Compton scattering electrons with a gas micro time projection chamber, is expected to open up MeV gamma-ray astronomy. The technical challenge for achieving several degrees of the point-spread function is precise determination of the electron recoil direction and the scattering position from track images. We attempted to reconstruct these parameters using convolutional neural networks. Two network models were designed to predict the recoil direction and the scattering position. These models marked 41$^\circ$ of angular resolution and 2.1 mm of position resolution for 75 keV electron simulation data in argon-based gas at 2 atm pressure. In addition, the point-spread function of the ETCC was improved to 15$^\circ$ from 22$^\circ$ for experimental data from a 662 keV gamma-ray source. The performance greatly surpassed that using traditional analysis.