寺田 幸功

FORCE is a 1.2 tonnes small mission dedicated for wide-band fine-imaging x-ray observation. It covers from 1 to 80 keV with a good angular resolution of $15"$ half-power-diameter. It is proposed to be launched around mid-2020s and designed to reach a limiting sensitivity as good as $F_X (10-40~{\rm keV}) = 3 \times 10^{-15}$~erg cm$^{-2}$ s$^{-1}$ keV$^{-1}$ within 1~Ms. This number is one order of magnitude better than current best one. With its high-sensitivity wide-band coverage, FORCE will probe the new science field of "missing BHs", searching for families of black holes of which populations and evolutions are not well known. Other point-source and diffuse-source sciences are also considered. FORCE will also provide the "hard x-ray coverage" to forthcoming large soft x-ray observatories.

<p>2016年2月17日に打ち上げられたX線衛星「ひとみ」(ASTRO-H)に搭載された軟ガンマ線検出器(Soft Gamma-ray Detector:SGD)の軌道動作実績について報告する。SGDは、3月15日より順次、センサーの立ち上げを行い、通信途絶となった3月26日まで、機能的には正常に動作させることができた。一部の天体からのガンマ線信号の取得に成功し、高感度ガンマ線観測を行う上で重要となる軌道上バックグランドのデータを得た。SGDで初めて実現したSi/CdTe半導体コンプトンカメラで得られたこれらのデータについて、報告を行う。</p>

© 2016 SPIE. The Focusing Optics X-ray Solar Imager (FOXSI) is, in its initial form, a sounding rocket experiment designed to apply the technique of focusing hard X-ray (HXR) optics to the study of fundamental questions about the high-energy Sun. Solar HXRs arise via bremsstrahlung from energetic electrons and hot plasma produced in solar flares and thus are one of the most direct diagnostics of are-accelerated electrons and the impulsive heating of the solar corona. Previous missions have always been limited in sensitivity and dynamic range by the use of indirect (Fourier) imaging due to the lack of availability of direct focusing optics, but technological advances now make direct focusing accessible in the HXR regime (as evidenced by the NuSTAR spacecraft and several suborbital missions). The FOXSI rocket experiment develops and optimizes HXR focusing telescopes for the unique scientific requirements of the Sun. To date, FOXSI has completed two successful flights on 2012 November 02 and 2014 December 11 and is funded for a third flight. This paper gives a brief overview of the experiment, which is sensitive to solar HXRs in the 4-20 keV range, describes its first two flights, and gives a preview of plans for FOXSI-3.

The radioactive decay of the freshly synthesized $r$-process nuclei ejected<br /> in compact binary mergers power optical/infrared macronovae (kilonovae) that<br /> follow these events. The light curves depend critically on the energy partition<br /> among the different products of the radioactive decay and this plays an<br /> important role in estimates of the amount of ejected $r$-process elements from<br /> a given observed signal. We study the energy partition and $\gamma$-ray<br /> emission of the radioactive decay. We show that $20$-$50\%$ of the total<br /> radioactive energy is released in $\gamma$-rays on timescales from hours to a<br /> month. The number of emitted $\gamma$-rays per unit energy interval has roughly<br /> a flat spectrum between a few dozen keV and $1$ MeV so that most of this energy<br /> is carried by $\sim 1$ MeV $\gamma$-rays. However at the peak of macronova<br /> emission the optical depth of the $\gamma$-rays is $\sim 0.02$ and most of the<br /> $\gamma$-rays escape. The loss of these $\gamma$-rays reduces the heat<br /> deposition into the ejecta and hence reduces the expected macronova signals if<br /> those are lanthanides dominated. This implies that the ejected mass is larger<br /> by a factor of $2$-$3$ than what was previously estimated. Spontaneous fission<br /> heats up the ejecta and the heating rate can increase if a sufficient amount of<br /> transuranic nuclei are synthesized. Direct measurements of these escaping<br /> $\gamma$-rays may provide the ultimate proof for the macronova mechanisms and<br /> an identification of the $r$-process nucleosynthesis sites. However, the<br /> chances to detect these signals are slim with current X-ray and $\gamma$-ray<br /> missions. New detectors, more sensitive by at least a factor of ten, are needed<br /> for a realistic detection rate.