236 research outputs found
On the solar cycle variation in the barometer coefficients of high latitude neutron monitors
Evaluation of barometer coefficients of neutron monitors located at high latitudes has been performed by using the results of the spherical harmonic analysis based on the records from around twenty stations for twelve years from January 1966 to December 1977. The average of data at eight stations, where continuous records are available for twelve years, show that the absolute value of barometer coefficient is in positive correlation with the cosmic ray neutron intensity. The variation rate of the barometer coefficient to the cosmic ray neutron intensity is influenced by the changes in the cutoff rigidity and in the primary spectrum
Electron-Positron Pairs in Hot Accretion Flows and Thin Disk Coronae
We investigate equilibrium accretion flows dominated by pairs. We
consider one- and two-temperature accretion disk coronae above a thin disk, as
well as hot optically thin two-temperature accretion flows without an
underlying thin disk; we model the latter in the framework of
advection-dominated accretion flows (ADAFs). In all three cases we include
equipartition magnetic fields. We confirm the previous result that the
equilibrium density of pairs in two-temperature ADAFs is negligible; and show
that the inclusion of magnetic fields and the corresponding synchrotron cooling
reduces the pair density even further. Similarly, we find that pairs are
unimportant in two-temperature coronae. Even when the corona has significantly
enhanced heating by direct transfer of viscous dissipation in the thin disk to
the corona, the inefficient Coulomb coupling between protons and electrons acts
as a bottleneck and prevents the high compactness required for pair-dominated
solutions. Only in the case of a one-temperature corona model do we find
pair-dominated thermal equilibria. These pair-dominated solutions occur over a
limited range of optical depth and temperature.Comment: 38 pages, including 10 figures, LaTeX; to appear in Ap
Recording system for the solar neutron monitoring at Mt. Norikura
To monitor solar neutron events, a new recording system will be installed at Mt. Norikura Cosmic Ray Observatory. The recording system is composed of a pulse counter with clock and a microcomputer with minifloppy disk. The counter and the microcomputer are connected through the General Purpose Interface Bus line. The one minute total count of the neutron monitor is recorded on the minifloppy disk
Developing and utilizing an Euler computational method for predicting the airframe/propulsion effects for an aft-mounted turboprop transport. Volume 2: User guide
This manual explains how to use an Euler based computational method for predicting the airframe/propulsion integration effects for an aft-mounted turboprop transport. The propeller power effects are simulated by the actuator disk concept. This method consists of global flow field analysis and the embedded flow solution for predicting the detailed flow characteristics in the local vicinity of an aft-mounted propfan engine. The computational procedure includes the use of several computer programs performing four main functions: grid generation, Euler solution, grid embedding, and streamline tracing. This user's guide provides information for these programs, including input data preparations with sample input decks, output descriptions, and sample Unix scripts for program execution in the UNICOS environment
Spectrum of Optically Thin Advection Dominated Accretion Flow around a Black Hole: Application to Sgr A*
The global structure of optically thin advection dominated accretion flows
which are composed of two-temperature plasma around black holes is calculated.
We adopt the full set of basic equations including the advective energy
transport in the energy equation for the electrons. The spectra emitted by the
optically thin accretion flows are also investigated. The radiation mechanisms
which are taken into accout are bremsstrahlung, synchrotron emission, and
Comptonization. The calculation of the spectra and that of the structure of the
accretion flows are made to be completely consistent by calculating the
radiative cooling rate at each radius. As a result of the advection domination
for the ions, the heat transport from the ions to the electrons becomes
practically zero and the radiative cooling balances with the advective heating
in the energy equation of the electrons. Following up on the successful work of
Narayan et al. (1995), we applied our model to the spectrum of Sgr A*. We find
that the spectrum of Sgr A* is explained by the optically thin advection
dominated accretion flow around a black hole of the mass M_bh=10^6 M_sun. The
parameter dependence of the spectrum and the structure of the accretion flows
is also discussed.Comment: AAS LaTeX file; 26 pages; 12 ps figures; to be published in ApJ. PDF
files are obtainable via following anonymous ftp.
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/manmoto/preprint/spec_sgrA.tar.g
Blob ejection from advection-dominated accretion flow: observational consequences
There is increasing evidence for the presence of an optically thin
advection-dominated accretion flow (ADAF) in low luminosity active galactic
nuclei and radio-loud quasars. The present paper is devoted to explore the fate
of a blob ejected from an ADAF, and to discuss its observational consequences.
It is inevitable for the ejected blob to drastically expand into its
surroundings. Consequently, it is expected that a group of relativistic
electrons should be accelerated, which may lead to nonthermal flares, since a
strong shock will be formed by the interaction between the blob and its
surroundings. Then the blob cools down efficiently, leading to the appearance
of recombination lines about s after its ejection from an ADAF. We apply
this model to NGC 4258 for some observational prediction, and to PKS 2149--306
for the explanation of observational evidence. Future simultaneous observations
of recombination X-ray lines and continuum emission are highly desired to test
the present model.Comment: 4 pages in emulateapj.sty, no figure. Accepted by ApJ Letter
Magnetic Exciton Mediated Superconductivity in the Hidden-Order Phase of URu2Si2
We propose the magnetic exciton mediated superconductivity occurring in the
enigmatic hidden-order phase of URu2Si2. The characteristic of the massive
collective excitation observed only in the hidden-order phase is well
reproduced by the antiferro hexadecapole ordering model as the trace of the
dispersive crystalline-electric-field excitation. The disappearance of the
superconductivity in the high-pressure antiferro magnetic phase can naturally
be understood by the sudden suppression of the magnetic-exciton intensity. The
analysis of the momentum dependence of the magnetic-exciton mode leads to the
exotic chiral d-wave singlet pairing in the Eg symmetry. The Ising-like
magnetic-field response of the mode yields the strong anisotropy observed in
the upper critical field even for the rather isotropic 3-dimensional Fermi
surfaces of this compound.Comment: 5 pages, 4 figure
Non-Collinear Magnetism due to Orbital Degeneracy and Multipolar Interactions
The origin of non-collinear magnetism under quadrupolar ordering is
investigated with CeB6 taken as a target system. The mode-mixing effect among
15 multipoles is analyzed based on the Ginzburg-Landau free energy. Then the
lower magnetic transition temperature and the order parameters are derived
within the mean-field approximation. In the presence of pseudo-dipole-type
interactions for the next-nearest neighbors, the observed pattern of
non-collinear ordering is indeed stabilized for certain set of interaction
parameters. The stability of the phase III' in the magnetic field is also
explained, which points to the importance of the next-nearest-neighbor
octupole-octupole interaction. Concerning the phase IV in CexLa1-xB6 with x ~
0.75, a possibility of pure octupole ordering is discussed based on slight
modifications of the strength of interactions.Comment: 12 pages, 7 figures, 3 tables, to appear in J. Phys. Soc. Jpn. 70 (6)
(2001
On the Hidden Order in URuSi --- Antiferro Hexadecapole Order and its Consequences
An antiferro ordering of an electric hexadecapole moment is discussed as a
promising candidate for the long standing mystery of the hidden order phase in
URuSi. Based on localized -electron picture, we discuss the
rationale of the selected multipole and the consequences of the antiferro
hexadecapole order of symmetry. The mean-field solutions and
the collective excitations from them explain reasonably significant
experimental observations: the strong anisotropy in the magnetic
susceptibility, characteristic behavior of pressure versus magnetic field or
temperature phase diagrams, disappearance of inelastic neutron-scattering
intensity out of the hidden order phase, and insensitiveness of the NQR
frequency at Ru-sites upon ordering. A consistency with the strong anisotropy
in the magnetic responses excludes all the multipoles in two-dimensional
representations, such as . The expected azimuthal angle
dependences of the resonant X-ray scattering amplitude are given. The
-type antiferro quadrupole should be induced by an in-plane
magnetic field along , which is reflected in the thermal expansion and
the elastic constant of the transverse mode. The
-type [-type] antiferro quadrupole is also induced by
applying the uniaxial stress along direction [ direction]. A
detection of these induced antiferro quadrupoles under the in-plane magnetic
field or the uniaxial stress using the resonant X-ray scattering provides a
direct redundant test for the proposed order parameter.Comment: 10 pages, 10 figures, 5 table
Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration
We consider stochastic particle acceleration in plasmas around stellar mass
black holes to explain the emissions above 1 MeV from Galactic black hole
candidates. We show that for certain parameter regimes, electrons can overcome
Coulomb losses and be accelerated beyond the thermal distribution to form a new
population, whose distribution is broad and usually not a power law; the peak
energy of the distribution is determined by the balance between acceleration
and cooling, with particles piling up around it. Radiation by inverse Compton
scattering off the thermal (from background) and non-thermal (produced by
acceleration) particles can in principle explain the hard X-ray to gamma-ray
emissions from black hole candidates. We present model fits of Cyg X-1 and GRO
J0422 in 50 keV -- 5 MeV region observed with OSSE and COMPTEL.Comment: 2 figures, to appear in March 20 of ApJ
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