Confirmation of Sgr A* Using the Event Horizon Telescope Data as Extreme Binary of the Supermassive Black Holes Concluded by Decameter Radio Wave Pulse Observations

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SC-triggered plasma waves observed by the Akebono satellite in the polar regions and the plasmasphere

Plasma wave phenomena associated with sudden commencements (SCs) were analyzed based on observations conducted with the Akebono satellite, which has been collecting data for more than 13 years (since March 1989). Simultaneous plasma wave observation data for 257 SCs reveal that enhanced plasma waves are observed with an exact one-to-one correspondence with the SCs throughout the entire observation region, including the polar and plasmasphere regions. Electromagnetic whistler mode and ion cyclotron waves are enhanced in the low latitude plasmasphere, while electrostatic whistler mode and electromagnetic ion cyclotron waves are generated in the polar region. The onset times of the SC-triggered plasma waves exhibit a delay or lead time characteristic, compared with the onset times of SCs identified by the Kakioka Magnetic Observatory, with a time resolution of 1 s. By comparing the difference in SCs and enhanced electron plasma waves onset times, the propagation route of the SC disturbances can be identified in the plasmasphere

Seasonal dependence of the vertical distributions of auroral kilometric radiation sources and auroral particle acceleration regions observed by the Akebono satellite

Seasonal variations in the vertical distributions of occurrence probabilities of auroral kilometnc radiation (AKR) sources and auroral acceleration regions indicated by upward-flowing ion (UFI) events were compared based on statistical analyses of plasma waves and energetic particles data observed by the Akebono satellite. The peak altitude in the vertical distribution of occurrence probability of AKR sources whose emission intensities were larger than -150dBW/m^2-Hz occurred at 5000-6000 km in the summer polar region and at 3000-4000 km in the winter polar region. The analyses have also clarified that the vertical distributions of occurrence probabilities of auroral acceleration regions also show seasonal variations that are quite similar to those of the AKR sources. Based on the observation that intense AKR emissions can be generated even in high-density plasma, we suggest that processes other than cyclotron maser instability (CMI), such as mode conversions, may be dominant under conditions of dense ambient plasma in the summer polar regions. The contri-bution of the emissions generated by these mechanisms to the seasonal variations in the vertical distributions of AKR sources is thought to be significant