Akihiro DOI

第35回宇宙構造・材料シンポジウム（2019年12月2日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)), 相模原市, 神奈川県著者人数: 14名資料番号: SA6000146022レポート番号: B-02

Balloon Symposium 2019 (November 7-8, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan

大気球シンポジウム 2019年度（2019年11月7-8日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 21名資料番号: SA6000140030レポート番号: isas19-sbs-030

The Event Horizon Telescope (EHT) recently produced the first horizon-scale image of a supermassive black hole. Expanding the array to include a 3-meter space telescope operating at >200 GHz enables mass measurements of many black holes, movies of black hole accretion flows, and new tests of general relativity that are impossible from the ground.

大気球シンポジウム 平成30年度（2018年11月1-2日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 27名資料番号: SA6000128002レポート番号: isas18-sbs-002

Balloon Symposium 2018 (November 1-2, 2018. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan

<p>人工衛星を用いたミッションの高度化に伴い，衛星搭載用のアンテナや望遠鏡といった衛星搭載機器も，より高精度であることが求められている．そのような高精度な機器の実現に向け，軌道上での変形を計測し，アクチュエータにより補正することで高い精度を得る形状可変構造システムが，多くの機関で研究・開発されている．著者らも積層型圧電素子と変位拡大機構を組み合わせたアクチュエータを用いてアンテナ反射鏡面の形状調整を行う形状可変鏡（スマート形状可変鏡）の研究・開発に取り組んでおり，製作したアクチュエータの性能評価や，実際のアンテナシステムに組み込んだ状態での形状可変鏡の有効性確認試験を実施している．本稿では，そのようなスマート形状可変鏡に関して，研究内容を紹介する．</p>

Balloon Symposium 2017 (November 9-10, 2017. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan

Copyright © (2017) by International Astronautical Federation. All rights reserved. A mechanism for the high-precision positioning of reflector segments by using kinematic couplings has been developed for balloon-borne radio telescopes, and the effectiveness of the mechanism is demonstrated through experiments. A high-precision reflector for radio telescopes is under development, and it is intended to be used for the observation of radio waves of up to 300 GHz. The reflector consists of six segments, a back structure, and a high-precision positioning mechanism. The high-precision positioning mechanism utilizes kinematic couplings, and the segments are positioned and fixed precisely to the back structure by the kinematic couplings. The positioning of the segments on the back structure is one of the largest sources of error in reflector systems. Therefore, kinematic couplings are important components of a reflector system for achieving a high surface accuracy. Three combinations of a ball and a V-groove are employed in the positioning mechanism. Load-applying mechanisms are used to apply and control pressing loads between the segment and back structure. In order to demonstrate the effectiveness of the mechanism, the positioning repeatability between a segment and a back structure was investigated through experiments. In these experiments, the reflector segment was attached to and detached from the back structure, and the relative positions of the reflector with respect to the back structure were measured using a photogrammetry system during the process of attachment. The cycle of attachment, measurement, and detachment was repeated five times, and the positioning repeatability was evaluated. A positioning accuracy of approximately 20 um RMS was achieved using the developed reflector system. The results demonstrate the effectiveness of the positioning mechanism, which incorporates kinematic couplings for the high-precision positioning of a reflector for a balloon-borne radio telescope.

Balloon Symposium 2016 (November 1-2, 2016. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The present paper reports the results of shape-control experiments using the smart secondary reflector prototype for satellite-borne radio-astronomy. The shape of the secondary reflector is modified by six special piezoelectric actuators with displacement magnification mechanisms. The experiments successfully demonstrated that the reception power of the antenna system has been improved by the shape control.

We report on results from new high-sensitivity, high-resolution 86GHz (3.5<br /> millimeter) observations of the jet base in the nearby radio galaxy M87,<br /> obtained by the Very Long Baseline Array in conjunction with the Green Bank<br /> Telescope. The resulting image has a dynamic range exceeding 1500 to 1, the<br /> highest ever achieved for this jet at this frequency, resolving and imaging a<br /> detailed jet formation/collimation structure down to ~10 Schwarzschild radii<br /> (Rs). The obtained 86GHz image clearly confirms some important jet features<br /> known at lower frequencies, i.e., a wide-opening angle jet base, a<br /> limb-brightened intensity profile, a parabola-shape collimation profile and a<br /> counter jet. The limb-brightened structure is already well developed at &lt;<br /> 0.2mas (&lt; 28Rs, projected) from the core, where the corresponding apparent<br /> opening angle becomes as wide as ~100 degrees. The subsequent jet collimation<br /> near the black hole evolves in a complicated manner; there is a &quot;constricted&quot;<br /> structure at tens Rs from the core, where the jet cross section is locally<br /> shrinking. We suggest that an external pressure support from the inner part of<br /> radiatively-inefficient accretion flow may be dynamically important in<br /> shaping/confining the footprint of the magnetized jet. We also present the<br /> first VLBI 86GHz polarimetric experiment for this source, where a highly<br /> polarized (~20%) feature is detected near the jet base, indicating the presence<br /> of a well-ordered magnetic field. As a by-product, we additionally report a<br /> 43/86 GHz polarimetric result for our calibrator 3C 273 suggesting an extreme<br /> rotation measure near the core.

大気球シンポジウム 平成27年度（2015年11月5-6日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県 Balloon Symposium 2015 (November 5-6, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 34名 資料番号: SA6000044037 レポート番号: isas15-sbs-037

大気球シンポジウム 平成27年度（2015年11月5-6日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県 Balloon Symposium 2015 (November 5-6, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 14名 資料番号: SA6000044038 レポート番号: isas15-sbs-038

The relativistic jet in M87 offers a unique opportunity for understanding the<br /> detailed jet structure and emission processes due to its proximity. In<br /> particular, the peculiar jet region HST-1 at ~1 arcsecond (or 80 pc, projected)<br /> from the nucleus has attracted a great deal of interest in the last decade<br /> because of its superluminal motion and broadband radio-to-X-ray outbursts,<br /> which may be further connected to the gamma-ray productions up to TeV energies.<br /> Over the last five years, we have been doing an intensive monitoring of HST-1<br /> with EVN at 5GHz in order to examine the detailed structural evolution and its<br /> possible connection to high-energy activities. While this program already<br /> yielded interesting results in terms of the detailed mas-scale structure,<br /> proper motion measurements and structural variations, the recent HST-1<br /> brightness is continuously decreasing at this frequency. To counter this, we<br /> have shifted our monitoring frequency to 1.7GHz from October 2013. This<br /> strategy successfully recovered the fainter emission that was missed in the<br /> last 5GHz session. Moreover, we again discovered the sudden emergence of a new<br /> component at the upstream edge of HST-1, demonstrating that the use of EVN<br /> 1.7GHz is indeed powerful to probe the current weak nature of HST-1. Here we<br /> report early results from the 1.7GHz monitoring as well as further progress on<br /> the long-term kinematic study.

The present paper reports the results of shape-control experiments using the smart secondary reflector prototype for satellite-borne radio-astronomy. The shape of the secondary reflector is modified by six special piezoelectric actuators with displacement magnification mechanisms. The experiments successfully demonstrated that the reception power of the antenna system has been improved by the shape control.

大気球シンポジウム 平成26年度（2014年11月6-7日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県 Balloon Symposium 2014 (November 6-7, 2014. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 26名 資料番号: SA6000021016 レポート番号: isas14-sbs-016

<title>Abstract</title>The nearby radio galaxy M87 offers a unique opportunity for exploring the connection between γ-ray production and jet formation at an unprecedented linear resolution. However, the origin and location of the γ-rays in this source is still elusive. Based on previous radio/TeV correlation events, the unresolved jet base (radio core) and the peculiar knot HST-1 at &gt;120 pc from the nucleus are proposed as candidate site(s) of γ-ray production. Here we report our intensive, high-resolution radio monitoring observations of the M87 jet with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from February 2011 to October 2012. During this period, an elevated level of the M87 flux is reported at TeV with VERITAS. We detected a remarkable flux increase in the radio core with VERA at 22/43 GHz coincident with the VHE activity. Meanwhile, HST-1 remained quiescent in terms of its flux density and structure at radio. These results strongly suggest that the TeV γ-ray activity in 2012 originates in the jet base within 0.03 pc (projected) from the central supermassive black hole.