Engineering topics

Maeda, K.

Publications and source records attributed to Maeda, K..

At least 19 records

NASA NTRS2014

The Broad-Lined Type Ic SN 2012ap and the Nature of Relativistic Supernovae Lacking a Gamma-Ray Burst Detection

We present ultraviolet, optical, and near-infrared observations of SN2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from −13 to +272 days past the B-band maximum of −17.4 +/- 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of v approx. 20,000 km s(exp. −1) that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (v approx. greater than 27,000 km s(exp. −1)). We use these observations to estimate explosion properties and derive a total ejecta mass of 2.7 Solar mass, a kinetic energy of 1.0×1052 erg, and a (56)Ni mass of 0.1−0.2 Solar mass. Nebular spectra (t > 200 d) exhibit an asymmetric double-peaked [O I] lambda lambda 6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN2012ap joins SN2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black-hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable properties including above-average environmental metallicities of Z approx. greater than Solar Z, moderate to high levels of host-galaxy extinction (E(B −V ) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] > 1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae.

nature↗

NASA NTRS2012

Discovery of an Unidentified Fermi Object as a Black Widow-Like Millisecond Pulsar

The Fermi Gamma-ray Space Telescope has revolutionized our knowledge of the gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the outer-gap model predicts different sites of emission for the radio and gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible in the radio. Here we report the discovery of a radio-quiet" gamma-ray emitting MSP candidate by using Fermi, Chandra, Swift, and optical observations. The X-ray and gamma-ray properties of the source are consistent with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical and X-ray data. We suggest that the source is a black widow-like MSP with a approx. 0.1 Stellar Mass late-type companion star. Based on the profile of the optical and X-ray light-curves, the companion star is believed to be heated by the pulsar while the X-ray emissions originate from pulsar magnetosphere and/or from intra-binary shock. No radio detection of the source has been reported yet and although no gamma-ray/radio pulsation has been found, we estimated that the spin period of the MSP is approx. 3-5 ms based on the inferred gamma-ray luminosity.

Kong, A. K. H.↗

NASA NTRS1992

Measurement of Jovian decametric Io-related source location and beam shape

The paper presents new information on the locations of the Io-related sources A and C (i.e., Io-A and Io-C) and on the shapes of their emission beams on the basis of measurements of the Jovian decametric activity that was recorded by Voyager 1 and 2. In two instances, the same dynamic spectral arc event in the recorded data of the two spacecraft was recorded, providing in each case an opportunity to observe the same emission beam over a wide range of frequencies from two considerably different directions. The propagation-corrected centroid times of each of the Voyager-1 arcs are found to be coincident with those of the corresponding Voyager-2 arc in a particular frequency range, but not at other frequencies. The hypothesis that emission beams are in the form of thin, almost conical sheets, the cone opening angle decreasing with increasing frequency, is confirmed. It is demonstrated that both the Io-A and Io-C sources were located near the northern foot of the magnetic flux tube that was connected to Io.

Maeda, K.↗

NASA NTRS1989

Multifrequency analysis of a decametric storm observed at Voyager 1 and ground-based observatories

Observations of a Jovian decametric non-Io-A noise storm made from Voyager 1, the University of Florida Radio Observatory, the University of Texas Radio Astronomy Observatory, and the Jupiter station at Goddard Space Flight Center at frequencies of 26.3, 22.2, 20.0, and 18.0 MHz were found to be correlated. The activity observed at the ground stations occurred 68 min after the corresponding activity at Voyager 1. After correction is made for propagation time differences, this delay is reduced to 34 min. It is demonstrated that at each frequency the envelope of the individual-event beams occurring during the storm (some or all of which are associated with dynamic spectral arcs) is a quasi-constant structure that corotates with the inner Jovian magnetosphere, and that the width of this envelope beam is frequency dependent. The width increases as frequency is decreased, mainly because of the change in position of the trailing-edge beam boundary. Evidence for a relatively slow temporal change in beam geometry is also presented.

Maeda, K.↗

NASA NTRS1988

Auroral origin of a component of Jupiter's decametric radiation

Simultaneous observations at about 22 MHz of an Io-unrelated component of Jovian decametric radiation from Voyagers 1 and 2 and from a ground-based observatory are analyzed to investigate the beam structure of the radiation and to locate the radio-emitting region. It is concluded that the radiation of this component is emitted in quasi-continuous beams that corotate with the Jovian inner magnetosphere and that each beam can be approximated by a sector of a hollow cone. The source locations are geometrically determined by fitting a hollow-cone beam model, based on the O4 magnetic field model, to the observations. The result indicates that the radio sources lie above the northern hemisphere and on the field lines that are connected with the ultraviolet aurora of the so-called active sector.

Maeda, K.↗

NASA NTRS1986

Hemispheric asymmetries of the thermospheric semiannual oscillation

An analysis of the data on the asymmetries of the terrestrial thermospheric semiannual oscillation (SAO), recorded by satellites, radar stations, and rocket soundings (Hedin, 1983), is presented. The possible sources for the thermospheric SAO are discussed. An interpretation is presented of the hemispheric asymmetries of the thermospheric SAO in terms of gravity-wave activities, in which the proposed mechanism is associated with the hemispheric asymmetries in the atmospheric circulation due to the orographic differences between the two hemispheres. Consideration is given to the energy requirements for the observed hemispheric difference in the thermospheric SAO. The overall evidence supporting the proposed interpretation is discussed.

Maeda, K.↗

NASA NTRS1985

Conjecture about a hurricane system in the Jovian atmosphere

Arguments are presented in support of the hypothesis that the Great Red Spot (GRS) of Jupiter is a giant hurricane, and that the same decription might apply to the smaller vortices such as the white and brown ovals (barges) on the surface of Jupiter. Estimates of the spin-down times constants for the white and brown oval vortices, indicate that the motions must be sustained by the continued release of internal energy. In analogy with the CISK mechanism for terrestrial hurricanes, transport of water vapor is identified as a possible latent energy source. On the basis of the large size and long life time of the GRS, (indicating extreme depth), it is suggested that the hurricane GRS hurricane may have been induced by meteor impact. Voyager 1 images of the GRS are provided.

Mayr, H. G.↗

NASA NTRS1984

North-south asymmetries of solar particle events in upper stratospheric ozone

Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on August 4, 1972 and January 25, 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flows in summer; and (4) topographic asymmetry between Northern and Southern Hemispheres. These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively.

Maeda, K.↗

NASA NTRS1984

Semiannual oscillation of stratospheric ozone

By applying spherical harmonic analysis to the ozone data obtained from the Nimbus-7 solar backscattered UV-radiation measurements for the period from November 1978 to October 1980, the following features of the semi-annual oscillation (SAO) in stratospheric ozone are revealed: (1) the equatorial ozone SAO has a broad maximum of the order of 0.5 (mixing ratio in micro-g/g) between the 10 mb and 3 mb levels, and the maximum shifts downward from 1 mb in June (and December) to 40 mb in November (and May); (2) amplitudes of polar ozone SAO's are larger than that of the equatorial SAO, with a major maximum at 2 mb which is 2 micro-g/g at 75 deg N and 0.8 micro-g/g at 75 deg S, respectively; (3) the inverse phase between the polar and tropical SAO which occurs around the 3 mb (about 40 km) level can be interpreted in terms of the temperature-dependent ozone chemistry and the poleward meridional transport of ozone by dynamical processes in the atmosphere.

Maeda, K.↗

NASA NTRS1984

Feasibility of determining cloud-top heights using the backscattered ultraviolet satellite observation technique

A technique for determining cloud-top height by means of backscattered ultraviolet (BUV) solar radiation is presented. Cloud-top heights can be inferred using this technique of both the BUV radiance and its degree of polarization are measured by a spacecraft and compared with theoretical values. The cases of satellites with high-inclination orbits and geosynchronous satellites are discussed here. Based on calculations of radiance and polarization, the resolutions of cloud-top height determinations are roughly estimated in both cases. The estimates show that inference is possible as long as the angle between the direction of the sun and the satellite from the point of interest in the atmosphere is larger than about 10 deg. The estimates also indicate that the cloud-top-height resolution depends on solar zenith angle theta(0) in the case of nadir observation by satellites in nonequatorial orbits: The resolution is about 0.5 km for theta(0) = 30 and about 0.3 km for larger theta(0). On the other hand, when observations are made by geosynchronous satellites, the resolution depends strongly on the latitude of the point of interest, alpha(1); a resolution within 0.4 km can be achieved for alpha(1) less than or equal to 65 deg (0.2 km resolution can be obtained for middle latitudes). Resolution becomes rapidly worse with increasing latitude, and alpha(1) = about 70 deg seems to be the limit of observations with this technique.

Aruga, T.↗

NASA NTRS1984

Beam structure of Jupiter's decametric radiation

Data from concurrent Voyager and earth-based observations demonstrate that the Jovian source A radio emissions are not correlated with Io's position and have a distinct cross-sectional shape. The recordings were made simultaneously at 21.811 and 21.860 MHz in 1979. Voyager 1 and ground-data exhibited 13 highly correlated storms, unlike the Io-B events. Correlations were also identified among storms measured by both spacecraft and the ground station. Start and end times and flux densities for the highly correlated storms were used to calculate the projected beam shape. The data matched predictions of a model of a storm emission beam envelope in the form of a curved sheet that corotates with the planet.

Maeda, K.↗

NASA NTRS1983

Asymmetries of the upper stratospheric ozone distribution between two hemispheres

In connection with the eccentricity of the earth's orbit, conditions of solar radiation are not strictly symmetrical for the two hemispheres. The intensity of solar irradiation is approximately 6.6 percent higher near perihelion than near aphelion. As the ozone densities in the upper stratosphere and mesosphere are mainly controlled by photochemical processes, the asymmetry of irradiation conditions for both hemispheres could result in corresponding asymmetries regarding the ozone content. The present investigation is concerned with this possibility. The investigation takes into account Nimbus-7 and Nimbus-4 satellite data. It is found that the hemispheric asymmetries of the ozone distribution in the summer mesosphere and upper stratosphere are fully ascribable to the hemispheric temperature differences due to the combined effects of the earth's orbital ellipticity and its tilted spin axis from the ecliptic plane. The wintertime hemispheric asymmetries imply the presence of additional effects.

Maeda, K.↗

NASA NTRS1982

A broadband VLF burst associated with ring current electrons

A determination is made of the source of a broadband VLF burst observed during the inbound plasmapause crossing of the explorer 45 spacecraft on April 2, 1972 in the late stage of a geomagnetic storm. Electric and magnetic receiver data from the satellite were spectrally analyzed, showing a 1-3 kHz whistler component and an emission broadening event comprising enhancement of the 1.0 and 1.78 kHz electric field intensities by several orders of magnitude. A corresponding and simulaneous enhancement of the ring current electrons was observed. The emission band spreading was attributed to the generation of quasi-electrostatic short wavelength whistler mode emissions by hot bi-maxwellian electrons surging into the domain of low density magnetized cold plasma. The inner edge of the plasma sheet, which was the source of the electrons, was not far from the event.

Maeda, K.↗

NASA NTRS1982

A broad-band VLF-burst associated with ring-current electrons

Frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma is known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed by Explorer 45 in a similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasielectrostatic whistler mode emission of short wavelength by hot bimaxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event.

Maeda, K.↗

NASA NTRS1981

VLF-emissions associated with ring current electrons - Off-equatorial observations

Simultaneous observations of magnetospheric VLF emissions and the associated enhancement of ring current electrons up to 15 deg geomagnetic latitudes are made by the Explorer 45. Using a 4 deg inclination of orbit with a tilt angle of the earth's magnetic dipole axis of 11 deg, microdensitometer scanning of wideband data indicates that the band of missing emissions in the off-equatorial whistler mode emissions appears at f(H0)/2. Intensities above f(H0)/2 appear very weak in contrast to those of near-equatorial emissions where f(H0) is the equatorial electron gyrofrequency corresponding to the local gyrofrequency at the satellite. Whistler mode waves are reflected from high latitudes to the equator inside the source region, and the intensities of those waves are shown to be insufficient to explain the observed emissions below f(H0)/2 at the equator. Results indicate that the superposition of two types of emissions from the same processes at different locations is not the main mechanism for the formation of the two-band chorus, and the dominant sources of these choruses are located at the + or - 5 deg geomagnetic latitude.

Maeda, K.↗

NASA NTRS1981

Frequency band broadening of magnetospheric VLF emissions near the equator

The broadening of the whistler mode VLF emission band has frequently been observed by the equatorially orbiting S3-A (Explorer 45) satellite outside the midnight sector of the plasmasphere, during periods of geomagnetic disturbance. Prior to the broadening, the band of this emission is narrow with a sharp gap at the half electron gyrofrequency. The gradual broadening of the emission band on the low-frequency side is associated with the simultaneously observed spreading of the anisotropy of the ring current electrons to higher and wider energy ranges. Using the modeled distribution function, the linear growth rates of the cyclotron instability are calculated numerically. The results suggest that broadening of the VLF emission band near the plasmasphere can be caused by spreading of the ring current electron anisotropy toward higher energies.

Maeda, K.↗

NASA NTRS1981

Stratospheric ozone response to a solar proton event - Hemispheric asymmetries

Large-scale stratospheric ozone reduction due to precipitating energetic solar protons is examined, based on the backscattered ultraviolet experiment on the Nimbus 4 satellite during the 1972 solar flare. Some chemical equations for the processes are outlined. Distinct asymmetries in the columnar ozone content, the amount of ozone depression, and their temporal variation above 4 mb level (about 38 km) were observed between the two hemispheres. These asymmetries are ascribed to the differences mainly in dynamics and partly in the solar illumination and the vertical temperature structure between the summer and the winter polar atmospheres.

Maeda, K.↗

NASA NTRS1980

A search for correlation between geomagnetic activity and stratospheric ozone

The total ozone column content (TOZ) measured from the Nimbus 4 BUV experiment is analyzed in geomagnetic coordinates to study a possible link between the solar corpuscular radiation and the lower stratosphere. Using planetary magnetic index Ap as a measure of the solar corpuscular radiation, it is shown that the correlation between TOZ and Ap, if any, occurs predominantly at high latitudes during winter seasons. This is typical of most of the claimed correlations between sun and weather and may be the result of the winter increase of planetary wave activity which by coincidence have periods comparable to magnetic activity. The fact that even major magnetic storms have no detectable effect on the stratospheric ozone during summer does not support a direct cause and effect relation between solar and stratospheric perturbations.

Chandra, S.↗