Search

The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo Collaboration (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify and observe an electromagnetic (EM) counterpart. We constructed web-based system which enabled us to obtain and share information of candidate host galaxies for the counterpart, and status of our observations. Candidate host galaxies were selected from the GLADE catalog with a weight based on the three-dimensional GW localization map provided by LVC. We conducted galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of observed galaxies. We performed galaxy-targeted follow-ups to 23 GW events during O3, and the maximum probability covered by our observations reached to 9.8%. Among them, we successfully started observations for 10 GW events within 0.5 days after the detection. This result demonstrates that our follow-up observation has a potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to $\sim$100~Mpc with a probability area of $\leq$ 500~deg$^2$., 25 pages, 10 figures, 3 tables, published at https://academic.oup.com/ptep/article/2021/5/05A104/6122445

Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales $t_{\rm E}$ because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales ($t_{\rm E} \lesssim 6~{\rm days}$) but also with very small angular Einstein radii ($\theta_{\rm E}\lesssim 0.05~{\rm mas}$) among the events that have been found in the 2016--2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Bayesian analysis conducted with the combined $t_{\rm E}$ and $\theta_{\rm E}$ constraint, it is estimated that the lens masses of the individual events are $0.051^{+0.100}_{-0.027}~M_\odot$, $0.044^{+0.090}_{-0.023}~M_\odot$, and $0.046^{+0.067}_{-0.023}~M_\odot/0.038^{+0.056}_{-0.019}~M_\odot$ and the probability of the lens mass smaller than the lower limit of stars is $\sim 80\%$ for all events. We point out that routine lens mass measurements of short time-scale lensing events require survey-mode space-based observations., Comment: 9 pages, 6 figures

We report the discovery of a planet in a binary that was discovered from the analysis of the microlensing event OGLE-2018-BLG-1700. We identify the triple nature of the lens from the fact that the complex anomaly pattern can be decomposed into two parts produced by two binary-lens events, in which one binary pair has a very low mass ratio of $\sim 0.01$ between the lens components and the other pair has a mass ratio of $\sim 0.3$. We find two sets of degenerate solutions, in which one solution has a projected separation between the primary and its stellar companion less than the angular Einstein radius $\thetae$ (close solution), while the other solution has a separation greater than $\thetae$ (wide solution). From the Bayesian analysis with the constraints of the event time scale and angular Einstein radius together with the location of the source lying in the far disk behind the bulge, we find that the planet is a super-Jupiter with a mass of $4.4^{+3.0}_{-2.0}~M_{\rm J}$ and the stellar binary components are early and late M-type dwarfs with masses $0.42^{+0.29}_{-0.19}~M_\odot$ and $0.12^{+0.08}_{-0.05}~M_\odot$, respectively, and the planetary system is located at a distance of $D_{\rm L}=7.6^{+1.2}_{-0.9}~{\rm kpc}$. The planet is a circumstellar planet according to the wide solution, while it is a circumbinary planet according to the close solution. The projected primary-planet separation is $2.8^{+3.2}_{-2.5}~{\rm au}$ commonly for the close and wide solutions, but the primary-secondary binary separation of the close solution, $0.75^{+0.87}_{-0.66}~{\rm au}$, is widely different from the separation, $10.5^{+12.1}_{-9.2}~{\rm au}$, of the wide solution., 10 pages, 8 figures

We present the discovery of a planet on a very wide orbit in the microlensing event OGLE-2012-BLG-0838. The signal of the planet is well separated from the main peak of the event and the planet-star projected separation is found to be twice larger than the Einstein ring radius, which roughly corresponds to a projected separation of ~4 AU. Similar planets around low-mass stars are very hard to find using any technique other than microlensing. We discuss microlensing model fitting in detail and discuss the prospects for measuring the mass and distance of lens system directly., Comment: 26 pages, 11 figures

Solar neutron observations are very important for understanding of nucleon acceleration mechanism in solar flares, but there are only a few tens of detection since the discovery in 1980. This is because most o solar neutron observations have been done from not space but the ground with insufficient sensitivity. We have designed very compact and high sensitive solar neutron and gamma-ray spectrometer utilizing a novel photo-sensor Silicon photo-multiplier (Si PM). This paper describes concept, design and performance of our detector for micro/nanosatellite applications.

Robot arms for humanoid are widely developed for medical, welfare and education use. Surface electromyogram (sEMG) signals which are the electrical signals obtained from surface of human skin using electrodes have been mainly used for classification of hand motions. However, it is difficult to classify detailed motions such as finger motions and wrist pronation or supination. Moreover, Kinect is an integration sensor device which can capture human joints movement. It also has been widely used for recognition of body motions in many fields. However, it has some problems such as setting of camera and restriction of detection range. In this study, we propose an advanced method of motion classification by combining arm-shape-changes with sEMG to classify the detailed motions. Arm-shape-changes are forearm deformation caused by a bulge of muscle when subjects move an arm or a finger. Experimental results showed classification accuracies of 90% or more in wrist pronation and supination which are difficult to classify using only sEMG signals. As the result, our method could classify the detailed motions and contribute to expansion of classifiable hand motions.