544 research outputs found
On the continuity of the magnetizing current density in 3-D magnetic field analysis with edge element
The effects of the continuity of the magnetizing current density on the convergence of the incomplete Cholesky conjugate gradient method and the accuracy of the calculated flux densities are investigated by imposing different continuity conditions for both nodal and edge elements. It is shown that the continuity condition should be imposed precisely in the case of edge elements </p
Generation of Alfven Waves by Magnetic Reconnection
In this paper, results of 2.5-dimensional magnetohydrodynamical simulations
are reported for the magnetic reconnection of non-perfectly antiparallel
magnetic fields. The magnetic field has a component perpendicular to the
computational plane, that is, guide field. The angle theta between magnetic
field lines in two half regions is a key parameter in our simulations whereas
the initial distribution of the plasma is assumed to be simple; density and
pressure are uniform except for the current sheet region. Alfven waves are
generated at the reconnection point and propagate along the reconnected field
line. The energy fluxes of the Alfven waves and magneto-acoustic waves (slow
mode and fast mode) generated by the magnetic reconnection are measured. Each
flux shows the similar time evolution independent of theta. The percentage of
the energies (time integral of energy fluxes) carried by the Alfven waves and
magneto-acoustic waves to the released magnetic energy are calculated. The
Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at
the maximum (theta=80^\circ) in the case of beta=0.1, 1, and 20 respectively,
where beta is the plasma beta (the ratio of gas pressure to magnetic pressure).
The magneto-acoustic waves carry 16.2% (theta=70^\circ), 25.9%
(theta=60^\circ), and 75.0% (theta=180^\circ) of the energy at the maximum.
Implications of these results for solar coronal heating and acceleration of
high-speed solar wind are discussed.Comment: Accepted for publication in PASJ. 24 pages, 11 figure
Practical analysis of 3-D dynamic nonlinear magnetic field using time-periodic finite element method
A practical 3-D finite element method using edge elements for analyzing stationary nonlinear magnetic fields with eddy currents in electric apparatus, in which the flux interlinking the voltage winding is given, has been proposed. The method is applied to the analysis of magnetic fields in the Epstein frame </p
RXTE Observations of the Low-Mass X-Ray Binary 4U 1608-522 in Upper-Banana State
To investigate the physics of mass accretion onto weakly-magnetized neutron
stars, 95 archival RXTE datasets of an atoll source 4U 1608-522, acquired over
1996-2004 in so-called upper-banana state, were analyzed. The object meantime
exhibited 3-30 keV luminosity in the range of <~ 10^35 - 4 x 10^37 erg s^-1,
assuming a distance of 3.6 kpc. The 3-30 keV PCA spectra, produced one from
each dataset, were represented successfully with a combination of a soft and a
hard component, of which the presence was revealed in a model-independent
manner by studying spectral variations among the observations. The soft
component is expressed by so-called multi-color disk model with a temperature
of ~1.8 keV, and is attributed to the emission from an optically-thick standard
accretion disk. The hard component is a blackbody emission with a temperature
of ~2.7 keV, thought to be emitted from the neutron-star surface. As the total
luminosity increases, a continuous decrease was observed in the ratio of the
blackbody luminosity to that of the disk component. This property suggests that
the matter flowing through the accretion disk gradually becomes difficult to
reach the neutron-star surface, presumably forming outflows driven by the
increased radiation pressure. On time scales of hours to days, the overall
source variability was found to be controlled by two independent variables; the
mass accretion rate, and the innermost disk radius which changes both
physically and artificially.Comment: ApJ accepted, 29 pages, 9 figure
ASCA Observations of the Central Regions of M31
Using ASCA, spatially integrated X-ray spectra of the central regions of M31
were studied. Data were accumulated over three different circular regions, with
the radii of 3', 6' and 12', all centered on the nucleus. The spectra are
relatively similar among the three regions. In the energy range above 1.5 keV,
the spectra are reproduced by a combination of a disk black-body component and
a black-body component, implying that the emission mainly comes from an
assembly of low-mass X-ray binaries. In energies below 1.5 keV, the spectra
involves two additional softer components, expressed with thin-thermal plasma
emission models of temperatures ~ 0.9 keV and ~ 0.3 keV. Over the central 12'
(2.4 kpc) region and in the 0.5-10 keV energy band, the binary component has a
luminosity of 2.6 x 10^{39} erg/s, while the two softer components both exhibit
luminosities of ~ 2 x 10^{38} erg/s. These results are compared with those from
other missions, including Chandra and XMM-Newton in particular. Discussion is
made on the nature of the two softer spectral components besides the binary
one.Comment: 12 pages, 8 figures and 5 tables; uses pasj00.cls; accepted for
Publications of the Astronomical Society of Japa
Suzaku Discovery of a Hard X-Ray Tail in the Persistent Spectra from the Magnetar 1E 1547.0-5408 during its 2009 Activity
The fastest-rotating magnetar 1E 1547.0-5408 was observed in broad-band
X-rays with Suzaku for 33 ks on 2009 January 28-29, 7 days after the onset of
its latest bursting activity. After removing burst events, the
absorption-uncorrected 2-10 keV flux of the persistent emission was measured
with the XIS as 5.7e-11 ergs cm-2 s-1, which is 1-2 orders of magnitude higher
than was measured in 2006 and 2007 when the source was less active. The
persistent emission was also detected significantly with the HXD in >10 keV up
to at least ~110 keV, with an even higher flux of 1.3e-10 ergs cm-2 s-1 in
20-100 keV. The pulsation was detected at least up to 70 keV at a period of
2.072135+/-0.00005 s, with a deeper modulation than was measured in a fainter
state. The phase-averaged 0.7-114 keV spectrum was reproduced by an absorbed
blackbody emission with a temperature of 0.65+/-0.02 keV, plus a hard power-law
with a photon index of ~1.5. At a distance of 9 kpc, the bolometric luminosity
of the blackbody and the 2-100 keV luminosity of the hard power-law are
estimated as (6.2+/-1.2)e+35 ergs s-1 and 1.9e+36 ergs s-1, respectively, while
the blackbody radius becomes ~5 km. Although the source had not been detected
significantly in hard X-rays during the past fainter states, a comparison of
the present and past spectra in energies below 10 keV suggests that the hard
component is more enhanced than the soft X-ray component during the persistent
activity.Comment: 12 pages, 7 figures, PASJ Vol.62 No.2 accepte
Iron Emission Lines on the Galactic Ridge Observed with Suzaku
In order to elucidate origin of the Galactic Ridge X-ray Emission, we
analyzed Suzaku data taken at various regions along the Galactic plane and
studied their Fe-K emission line features. Suzaku resolved the Fe line complex
into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines
from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The
6.7 keV line is clearly seen in all the observed regions and its longitudinal
distribution is consistent with that determined from previous observations. The
6.4 keV emission line was also found in various Galactic plane regions (b~0).
Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines
between the Galactic plane and the Galactic center regions are studied and its
implication is discussed.Comment: Accepted for publication in PASJ Suzaku 3rd special issu
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