Masanori Nishio

Quadrupolar Magnetic Reconnection in Solar Flares. I. Three-dimensional Geometry Inferred from Yohkoh Observations

We analyze the three-dimensional geometry of solar flares that show so-called interacting flare loops in soft X-ray, hard X-ray, and radio emission, as previously identified by Hanaoka and Nishio. The two flare loops that appear brightest after the flare are assumed to represent the outcome of a quadrupolar magnetic reconnection process, during which the connectivity of magnetic polarities is exchanged between the four loop footpoints. We parameterize the three-dimensional geometry of the four involved magnetic field lines with circular segments, additionally constrained by the geometric condition that the two pre-reconnection field lines have to intersect each other at the onset of the reconnection process, leading to a 10 parameter model. We fit this 10 parameter model to Yohkoh Soft and Hard X-Ray Telescopes (SXT and HXT) data of 10 solar flares and determine in this way the loop sizes and relative orientation of interacting field lines before and after reconnection. We apply a flare model by Melrose to calculate the magnetic flux transfer and energy released when two current-carrying field lines reconnect to form a new current-carrying system in a quadrupolar geometry. The findings and conclusions are the following. (1) The pre-reconnection field lines always show a strong asymmetry in size, consistent with the scenario of newly emerging small-scale loops that reconnect with preexisting large-scale loops. (2) The relative angle between reconnecting field lines is nearly collinear in half of the cases, and nearly perpendicular in the other half, contrary to the antiparallel configuration that is considered to be most efficient for magnetic reconnection. (3) The angle between interacting field lines is reduced by ≈10°-50° after quadrupolar reconnection. (4) The small-scale flare loop experiences a shrinkage by a factor of 1.31 ± 0.44, which is consistent with the scaling law found from previous electron time-of-flight measurements, suggesting that electron acceleration occurs near the cusp of quadrupolar configurations. (5) The large-scale loop is found to dominate the total induction between current-carrying loops, providing a simple estimate of the maximum magnetic energy available for flare energy release because of current transfer, which scales as ΔEI ≈ 1029.63(r2/109 cm)(I2/1011A)2 (with r2 the curvature radius and I2 the current of the large-scale loop) and is found to correlate with observed flare energies deduced from soft X-ray and hard X-ray fluxes. Most of the energy is transferred to small-scale loops that have one-half of the large-scale current (I1 = I2/2). (6) The quadrupolar reconnection geometry provides also a solution of Canfields dilemma of the offset between the maximum of vertical currents and the HXR flare loop footpoints. (7) The quadrupolar geometry provides not only a framework for interacting double-loop flares, but it can also be considered as a generalized version of (cusp-shaped) single-loop flares.

Development of an ultrastable fiber optic frequency distribution system using an optical delay control module [for frequency standard and VLBI]

An ultrastable fiber optic frequency distribution system is described. The ultrastable phase stability is achieved by configuring a closed phase-locked loop with a single-mode optical fiber transmission line in which two optical carrier signals with different wavelengths are transmitted as a forward and a backward signal, and installing an optical delay control module which has no differential dispersion effect between the two optical carrier waves and induces no electrical noise. A phase stabilized optical fiber (PSOF) is used for the signal transmission line. The stabilities of this system are 7.5/spl times/10/sup -17/ and 1.1/spl times/10/sup -17/ in Allan standard deviation at 1000 and 10000 s averaging time, respectively, while the environmental temperature of the PSOF cable varies as much as the range of 10/spl deg/C and the rate of 10/spl deg/C/12 h.

3-D Kinematics of Water Masers in the W 51A Region

We report proper motion measurements of water masers in the massive-star forming region W51A and the analyses of the 3-D kinematics of the masers in three maser clusters of W51A (W51 North, Main, and South). In W~51 North, we found a clear expanding flow that has an expansion velocity of ~70 km/s and indicates deceleration. The originating point of the flow coincides within 0.1 as with a silicon-monoxide maser source near the HII region W~51d. In W51 Main, no systematic motion was found in the whole velocity range (158 km/s =< V(lsr) =< -58 km/s) although a stream motion was reported previously in a limited range of the Doppler velocity (54 km/s =< V(lsr) =< 68 kms). Multiple driving sources of outflows are thought to explain the kinematics of W51 Main. In W51 South, an expansion motion like a bipolar flow was marginally visible. Analyses based on diagonalization of the variance-covariance matrix of maser velocity vectors demonstrate that the maser kinematics in W51 North and Main are significantly tri-axially asymmetric. We estimated a distance to W51 North to be 6.1 +/- 1.3 kpc on the basis of the model fitting method adopting a radially expanding flow.

Statistical Characteristics of atmospheric phase fluctuations observed by a VLBI system using a beacon wave from a geostationary Satellite

This paper reports the statistical characteristics of phase fluctuations obtained by a very long baseline interferometry, which received beacon waves from a geostationary satellite. Observations were made in different weather conditions by the 6-m Kagoshima and the 10-m Mizusawa radio telescopes, which were 1284 km apart from one another. Atmospheric phase fluctuations ranging from 0.2 to about 1000 s were detected. To study a variety of statistical characteristics of these phase fluctuations, the Allan standard deviation, /spl sigma//sub y/(/spl tau/), the temporal structure function, D/sub /spl phi//(/spl tau/), and the square root of power spectrum, G/sub /spl phi//(f), were calculated from the observation results. These qualities were found to depend on the time interval /spl tau/ or the frequency f (f=1/2/spl tau/) as follows: /spl sigma//sub y/(/spl tau/)/spl prop//spl tau//sup -0.6/, /spl tau//sup -0.3/, D/sub /spl phi//(/spl tau/)/spl prop//spl tau//sup 0.9/, /spl tau//sup 1.3/ for 0.2 sf>0.33 Hz and G/sub /spl phi//(f)/spl prop/f/sup -1.3/ for 0.33 Hz>f>0.00125 Hz. The curves of /spl sigma//sub y/(/spl tau/) and D/sub /spl phi//(/spl tau/) exhibited shifts whose magnitudes followed the weather order clear, cloudy, and rainy. For /spl tau/>1.5 s (or f<0.33 Hz), the experimental results were consistent with the theoretical values predicted by Kolmogorovs turbulence theory and a frozen-screen model, but for /spl tau/<1.5 s (or f>0.33 Hz), the model has to be modified to explain the experimental results.

J-Net Galactic-Plane Survey of VLBI Radio Sources for VLBI Exploration of Radio Astrometry (VERA)

In order to search for new VLBI sources in the Galactic plane that can be used as phase reference sources in differential VLBI, we have conducted 22 GHz observations of radio sources in the Galactic plane using the Japanese VLBI Network (J-Net). We have observed 267 VLBI source candidates selected from existing radio surveys and have detected 93 sources at the signal-to-noise ratio larger than 5. While 42 of the 93 detected sources had already been detected with VLBI at relatively lower frequency (typically 2 to 8 GHz), the remaining 51 are found to be new VLBI sources detected for the first time. These VLBI sources are located within

Orbit Determination using Radio Interferometer of Small-Diameter Antennas for LEO Satellites

|b|\le 5^\circ

Observation Site Atmospheric Phase Fluctuations Observed by Three-Element VLBI

, and have a large number of Galactic maser sources around them. Thus, they are potential candidates for phase reference sources for VLBI Exploration of Radio Astrometry (VERA), which is the first VLBI array dedicated to the phase referencing VLBI astrometry aiming at measuring the parallax and proper motion of maser sources in the whole Galaxy.

VLBI Observations of Water Masers in the Circumstellar Envelope of IRC+60169

The method of orbit determination using radio interferometer of small-diameter antennas for low-Earth-orbit (LEO) satellites is proposed. In this method, cross correlation phases are measured between received signals by two antennas. From numerical simulations and real observations analyses using a new software we have developed, orbit determination filter (ODEF), it is confirmed that the satellite position and velocity can be estimated with an accuracy of a few tens of meters and a few tens of mm/s for baseline length of 75 m and the altitude of the satellite of 1400 km. In addition, a numerical simulation makes clear that the position error becomes smaller as the baseline length gets longer.

Compact Microwave Transmitter on board a Pico-satellite for Atmospheric Water Vapor Observations

The beacon signals from a geostationary satellite were observed using three-element very long baseline interferometry (VLBI), and the phase fluctuations along the baselines between three sites were obtained. The atmospheric phase fluctuations at each observation site were derived from the baseline phase fluctuation data. The fluctuations were classified into three time-interval regions based on the dependence of the Allan standard deviation of the fluctuations on the time interval. In the region where the interval was less than a few seconds and in the one where it was greater than one hundred seconds, the curve of the Allan standard deviation was steep and showed the property of white phase noise. In the region between these two regions, the dependence of the Allan standard deviation on the time interval was weak. The magnitude of the Allan standard deviations for the three observation sites showed time variations in the region where the time interval was longer than a few seconds. Comparison with the weather conditions suggested that the time variations of the Allan standard deviation reflected atmospheric instability above the sites.

Magnetic field configuration in impulsive solar flares revealed with Yohkoh and Nobeyama Radioheliograph

Water masers around an AGB star IRC+60169 have been observed at four epochs using the Japanese VLBI networks. The distribution of the red-shifted features exhibits a ring-like structure, the size of which is 30 mas and corresponds to the inner radius of the maser shell. This implies that dense gas around the star obscures red-shifted emission