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著者人数: 15名, Accepted: 2019-11-14, 資料番号: SA1190207000

著者人数: 12名, Accepted: 2019-02-03, 資料番号: SA1180304000

The Mobile Asteroid Scout (MASCOT) is a small lander on board the Hayabusa2 mission of the Japan Aerospace Exploration Agency to the asteroid 162173 Ryugu. Among the instruments on MASCOT is a fluxgate magnetometer, the MASCOT Magnetometer (MasMag). The magnetometer is a lightweight ( ∼280 g∼280 g ) and low power ( ∼0.5 W∼0.5 W ) triaxial fluxgate magnetometer. Magnetic field measurements during the landing period and during the surface operational phase shall provide information about any intrinsic magnetic field of the asteroid and its remanent magnetization. This could provide important constraints on planet formation and the thermal and aqueous evolution of primitive asteroids., Thomas F. Peterson, United States. National Aeronautics and Space Administration. Emerging Worlds Program

By accident, Fig. 4 of the mentioned paper contains an error. In the fourth panel from the top, which shows the perpendicular and parallel temperatures of the hot proton component, the values on the vertical axis was half as high as the correct ones. Figure 4 should be replaced, although descriptions of the hot component temperatures in the text were correct. The postal code of ISAS/JAXA, which some of the authors belong to, should be corrected to 229-8510.

著者人数: 13名, Accepted: 2018-02-20, 資料番号: SA1170287000

著者人数: 15名, Accepted: 2018-09-05, 資料番号: SA1180175000

Accepted: 2015-10-09, 資料番号: SA1150297000

A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn's bow shock has revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream-downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ~100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures., 23 pages, 4 figures. Accepted for publication in ApJ

Accepted: 2013-04-22, 資料番号: SA1004678000

著者人数: 13名, 資料番号: SA1004426000

The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (, 22 pages, 5 figures. Accepted for publication in ApJ

Accepted: 2011-09-26, 資料番号: SA1003067000

Accepted: 2011-04-05, 資料番号: SA1003062000

著者人数: 11名, Accepted: 2010-03-09, 資料番号: SA1002789000

著者人数: 13名, Accepted: 2011-01-06, 資料番号: SA1002791000

著者人数: 11名, Accepted: 2015-07-25, 資料番号: SA1150172000

Accepted: 2001-01-11, 資料番号: SA1002542000

著者人数：11名, 資料番号: SA1002455000

Accepted: 1998-07-01, 資料番号: SA1002527000

著者人数: 22名, Accepted: 2011-06-10, 資料番号: SA1003260000

Energetic electrons of up to tens of MeV are created during explosive phenomena in the solar corona. While many theoretical models consider magnetic reconnection as a possible way of generating energetic electrons, the precise roles of magnetic reconnection during acceleration and heating of electrons still remain unclear. Here we show from 2D particle-in-cell simulations that coalescence of magnetic islands that naturally form as a consequence of tearing mode instability and associated magnetic reconnection leads to efficient energization of electrons. The key process is the secondary magnetic reconnection at the merging points, or the `anti-reconnection', which is, in a sense, driven by the converging outflows from the initial magnetic reconnection regions. By following the trajectories of the most energetic electrons, we found a variety of different acceleration mechanisms but the energization at the anti-reconnection is found to be the most important process. We discuss possible applications to the energetic electrons observed in the solar flares. We anticipate our results to be a starting point for more sophisticated models of particle acceleration during the explosive energy release phenomena., 14 pages, 12 figures (degraded figure quality), 1 table. Accepted for publication in ApJ.

著者人数：20名, Accepted: 2008-02-15, 資料番号: SA1000784000

Through the effort to obtain clues toward understanding of transport of cold plasma in the near-Earth magnetotail under northward IMF, we find that two-component protons are observed in the midnight plasma sheet (−10>XGSM>−30 RE, |YGSM| RE) under northward IMF by the Geotail spacecraft. Since the two-component protons are frequently observed on the duskside during northward IMF intervals but hardly on the dawnside, those found in the midnight plasma sheet are thought to come from the dusk flank. The cold proton component in the midnight region occasionally has a parallel anisotropy, which resembles that in the tail flank on the duskside. The flows in the plasma sheet with two-component protons were quite stagnant or slightly going dawnward, which supports the idea that the observed two-component protons in the midnight region are of duskside origin. Because the two-component protons in the midnight plasma sheet emerge under strongly northward IMF with the latitudinal angle larger than 45 degrees, and because the lag from the strongly northward IMF to the emergence can be as short as a few hours, we suggest that prompt plasma transport from the dusk to midnight region occurs under strongly northward IMF. We propose that the dawnward flows result from viscous interaction between the high-latitude portion of the plasma sheet and the lobe cell. Another candidate for plasma transport process from the dusk to the midnight region is turbulent flow due to vortical structures of the Kelvin-Helmholtz instability that developed around the dusk low-latitude boundary under strongly northward IMF. In addition, we also suggest that gradual cooling of hot protons under northward IMF is a global phenomenon in the near-Earth magnetotail.

Accepted: 2006-06-09, 資料番号: SA1000427000

Accepted: 2013-12-10, 資料番号: SA1140016000