On August 17th, 2017, three interferometric gravitational wave detectors of LIGO-Virgo collaboration observed the first gravitational wave signal from a binary neutron star merger. The constrained sky localization of the event allowed follow-up observations of the optical counterpart by telescopes. This was the moment that multi-messenger astronomy with gravitational waves became a reality.
On August 17, 2017, gravitational-wave telescopes detected gravitational waves from a binary neutron star merger. In this article, we outline the results of the gravitational-wave observation and their follow-up observations of electromagnetic counterparts, and then, we describe our interpretation for this event based on our numerical-relativity results.
GW170817, the first gravitational wave source from a neutron star merger, has also been observed by electromagnetic waves over a wide wavelength range. This marked the dawn of “multi-messenger” astronomy by the synergy of gravitational waves and electromagnetic waves. Neutron star mergers have been expected to synthesize elements heavier than iron, and emit optical/infrared signals by radioactive decays of newly synthesized elements. Therefore, optical/infrared observations of the counterpart of GW170817 provided unique information about nucleosynthesis in the neutron star merger. In this article, I review what we learned about nucleosynthesis in neutron star mergers and the origin of heavy elements in the Universe through the multi-messenger observations of GW170817.
The first binary neutron star merger, GW170817, was discovered by Advanced LIGO and Virgo on the 17th of August 2017. This merger was followed by multi-wavelength electromagnetic counterparts including: γ-ray pulse, optical-infrared kilonova, and non-thermal afterglow. In this article, we focus on the interpretation of the radio and X-ray afterglow. The observed spectra are well described by a single power law, suggesting that synchrotron radiation arising from the shock formed between the merger outflow and interstellar medium. Measuring the light curve of synchrotron afterglow allows us to study the outflow’s kinetic energy and velocity. Unlike the typical GRB afterglow, the afterglow of GW170817 rises at ∝t 0.8 from～10 day to at least～100 day. We show that the observations currently support the scenario in which a quasi-spherical outflow with a velocity gradient produces the afterglow. It is also worth noting that a simple top-hat jet model is ruled out from the observed data. Finally, we demonstrate how VLBI observation will allow us to directly measure the size of the outflow.
The gravitational wave event GW170817 from coalescence of two neutron stars is associated with various electromagnetic counterparts, and became a historical event telling the arrival of full-fledged multi-messenger era. In this manuscript, I explain the origin of the short gamma-ray burst sGRB 170817A simultaneously observed with this event. This event is much fainter than ordinary sGRBs, leading to hot discussions about its origin, whether it comes from a success jet observed from off-axis or a failed jet in penetrating the merger ejecta. We expect that the long-standing mystery of the origin of sGRBs will be finally resolved by future observations of X-ray and radio afterglows and gravitational waves. I also mention my struggle with the embargo on this event.
Topological phases of matter have been extensively studied both theoretically and experimentally for their characteristic band structures and exotic transport phenomena. Here, we review quantum anomalous Hall effect as one such example from the viewpoint of topological phases and related experimental results. Quantum anomalous Hall effect has been observed in a magnetic topological insulator Cr doped (Bi1-y Sby)2Te3 thin films, where the spontaneous magnetization induces one-dimensional chiral transport at the edge of the sample. Recent experiments have demonstrated the existence of the chiral edge conduction also along the magnetic domain wall in the sample. By introducing Landauer Büttiker formula, the one-to-one correspondence between the fabricated domain wall and the chiral edge conduction was confirmed. This enables us to construct reconfigurable dissipationless circuit with the control of the domain structure.
Flash memory with NAND structure (NAND flash memory) is widely used for mobile devices, cell phones, PC’s, and for storage devices in the internet-data-center recently. Conventional two-dimensional (2D) NAND flash memory has serious problems to realize the shrinkage of cell size beyond the 15 nm generation. In order to overcome the problems, two novel nano-technologies, namely Punch & Plug process and BiCS FLASH, have been developed. These innovations have resulted in commercially viable 3D flash memory, providing key technologies for fast, low-energy consumption and high-density memory devices. In this review, we discuss this state-of-the-art 3D flash memory technology.
We theoretically investigate mechanisms of high-order harmonic generation (HHG) in solids. A new theoretical framework presented here holds legitimacy of Bloch theorem even under an influence of the high-intensity electric field. Our theoretical framework shows the nonadiabatic processes, namely, AC Zener tunneling and semimetallization of semiconductors, are key factors for non-perturbative mechanisms of HHG. These mechanisms are classified by the field intensity with respect to the band gap energy and could be understood by an extended simple man model based on the analogy between tunnel ionization in gaseous media and Zener tunneling in semiconductors. These conclusions would stimulate universal understandings of HHG mechanisms in both atomic and solid cases.