Masato Kagitani

Evidence for global electron transportation into the jovian inner magnetosphere

Hot electron plasma moves in from Io Scientists have known that solar radiation ionizes the gases from Ios volcanoes to create a torus of plasma around Jupiter, but how that plasma moves is unclear. To investigate this, Yoshioka et al. monitored the temperature of the hot electron plasma as a function of distance from the planet with the Hisaki Earth-orbiting satellite. The fraction of hot electrons decreases only gradually with distance from Jupiter, which implies a rapid resupply of these electrons from outside Ios orbit. Science, this issue p. 1581 Near-Earth satellite measurements in the extreme ultraviolet examine a charged torus produced by volcanoes on Jupiter’s moon Io. Jupiter’s magnetosphere is a strong particle accelerator that contains ultrarelativistic electrons in its inner part. They are thought to be accelerated by whistler-mode waves excited by anisotropic hot electrons (>10 kiloelectron volts) injected from the outer magnetosphere. However, electron transportation in the inner magnetosphere is not well understood. By analyzing the extreme ultraviolet line emission from the inner magnetosphere, we show evidence for global inward transport of flux tubes containing hot plasma. High-spectral-resolution scanning observations of the Io plasma torus in the inner magnetosphere enable us to generate radial profiles of the hot electron fraction. It gradually decreases with decreasing radial distance, despite the short collisional time scale that should thermalize them rapidly. This indicates a fast and continuous resupply of hot electrons responsible for exciting the whistler-mode waves.

Primary Black Hole Spin in OJ 287 as Determined by the General Relativity Centenary Flare

OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical outburst in 2015 December. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole,

Inter-University upper Atmosphere Global Observation Network (IUGONET)

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First optical observation of the Moon's sodium exosphere from the lunar orbiter SELENE (Kaguya)

. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2% accuracy level, and it opens up the possibility of testing the black hole no-hair theorem with 10% accuracy during the present decade.

Response of Jupiter's inner magnetosphere to the solar wind derived from extreme ultraviolet monitoring of the Io plasma torus

An overview of the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project is presented with a brief description of the products to be developed. This is a Japanese inter-university research program to build the metadata database for ground-based observations of the upper atmosphere. The project also develops the software to analyze the observational data provided by various universities/institutes. These products will be of great help to researchers in efficiently finding, obtaining, and utilizing various data dispersed across the universities/institutes. This is expected to contribute significantly to the promotion of interdisciplinary research, leading to more a comprehensive understanding of the upper atmosphere.

Properties of hot electrons in the Jovian inner magnetosphere deduced from extended observations of the Io Plasma Torus

The first successful observations of resonant scattering emission from the lunar sodium exosphere were made from the lunar orbiter SELENE (Kaguya) using TVIS instruments during the period 17–19 December, 2008. The emission intensity of the NaD-line decreased by 12±6%, with an average value of 5.4 kR (kilorayleighs) in this period, which was preceded, by 1 day, by enhancement of the solar proton flux associated with a corotating interaction region. The results suggest that solar wind particles foster the diffusion of sodium atoms or ions in the lunar regolith up to the surface and that the time scale of the diffusion is a few tens of hours. The declining activity of the Geminid meteor shower is also one possible explanation for the decreasing sodium exosphere.

The Upper Atmosphere and Plasma Imager/the Telescope of Visible Light (UPI/TVIS) onboard the Kaguya spacecraft

Because Jupiters magnetosphere is huge and is rotationally dominated, solar wind influence on its inner part has been thought to be negligible. Meanwhile, dawn-dusk asymmetric features of this region have been reported. Presence of dawn-to-dusk electric field is one of the leading explanations of the asymmetry; however, the physical process of generating such an intense electric field still remains unclear. Here we present long and continuous monitoring of the extreme ultraviolet emissions from the Io plasma torus in Jupiters inner magnetosphere made by the Hisaki satellite between December 2013 and March 2014. We found five occasions where the dusk/dawn brightness ratio was enhanced above 2.5 in response to rapid increase of the solar wind dynamic pressure. The enhancement is achieved as the dusk region brightens and the dawn region dims. The observation indicates that dawn-to-dusk electric field in the inner magnetosphere is enhanced under compressed conditions.

Periodic variations of oxygen EUV dayglow in the upper atmosphere of Venus: Hisaki/EXCEED observations

One of the focal points of interest in Jovian magnetospheric physics is the transport of energy and particles into the inner region. While an explosive energy release event in the midmagnetosphere is manifested as an aurora transient, its connection to the inner part has not been investigated due to sparsity of observations. Here we take the advantage of long-term and quasi-continuous simultaneous monitoring of the polar aurora and the Io Plasma Torus (IPT) located in the inner magnetosphere by Extreme Ultraviolet Spectroscope for Exospheric Dynamics/Hisaki. Studies on temporal characteristics over hours enable us to see slow (~10 h) coupling between the middle and inner magnetosphere as well as to quantify the temperature of hot electrons in the IPT. We derive parameters that characterize the strong particle acceleration process.

Vertical emissivity profiles of Jupiter's northern H3+ and H2 infrared auroras observed by Subaru/IRCS

The Upper Atmosphere and Plasma Imager (UPI) was placed in a lunar orbit in order to study both the Moon and Earth. The UPI consists of two telescopes: a Telescope of Extreme Ultraviolet (TEX) and a Telescope of Visible Light (TVIS), which are both mounted on a two-axis gimbals system. The TVIS is equipped with fast catadioptric optics and a high-sensitivity CCD to image swift aurora and dark airglow in the terrestrial upper atmosphere. TVIS has a field-of-view equivalent to the Earth’s disk as seen from the Moon. The spatial resolution is about 30 km × 70 km on the Earth’s surface at auroral latitudes. The observation wavelengths can be changed by selecting different bandpass filters. Using the images of the northern and southern auroral ovals taken by TVIS, the intensities and shapes of the conjugate auroras will be quantitatively compared. Using the airglow imaging, medium- and large-scale ionospheric disturbances will be studied. In this paper, the instrumental design and performance of TVIS are presented.

Development of infrared Echelle spectrograph and mid-infrared heterodyne spectrometer on a small telescope at Haleakala, Hawaii for planetary observation

Using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) aboard Hisaki and the Solar Extreme Ultraviolet Monitor on the Solar and Heliospheric Observatory, we investigate variations of the extreme ultraviolet (EUV) dayglow brightness for OII 83.4 nm, OI 130.4 nm, and OI 135.6 nm in the Venusian upper atmosphere observed in March–April (period 1), April–May (period 2), and June–July (period 3) in 2014. The result shows that characteristic periodicities exist in the dayglow variations other than the ~27 day solar rotational effect of the solar EUV flux: 1.8, 2.8, 3.1, 4.5, and 9.9 day in period 1; 1.1 day in period 2; and 1.0 and 11 day in period 3. Many of these periodicities are consistent with previous observations and theory. We suggest these periodicities are related to density oscillations of oxygen atoms or photoelectrons in the thermosphere. The cause of these periodicities is still uncertain, but planetary-scale waves and/or gravity waves propagating from the middle atmosphere, and/or minor periodic variations of the solar EUV radiation flux may play a role. Effects of the solar wind parameters (velocity, dynamic pressure, and interplanetary magnetic fields intensity) on the dayglow variations are also investigated using the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) and magnetometer aboard Venus Express. Although clear correlation with the dayglow variations is not found, their minor periodicities are similar to the dayglow periodicities. Contribution of the solar wind to the dayglow remains still unknown, but the solar wind parameters might affect the dayglow variations.