1,189 research outputs found
A hybrid pulse transformer with permanent magnets
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Ac Susceptibility and Static Magnetization Measurements of CeRuSi at Small Magnetic Fields and Ultra Low Temperatures
The magnetic properties of CeRuSi at microkelvin temperatures (down
to 170 K) and ultra small magnetic fields ( mT) are
investigated experimentally for the first time. The simultaneously measured ac
susceptibility and static magnetization show neither evidence of the magnetic
ordering, superconductivity down to the lowest temperatures nor conventional
Landau Fermi-Liquid behavior. The results imply the magnetic transition
temperature in undoped CeRuSi is very close to absolute 0 K. The
possibility for proximity of CeRuSi to the quantum critical point
without any doping is discussed.Comment: 4 pages, 3 figures; accepted for publication in Phys. Rev. B (Rapid
Communication) and scheduled issue on 1st of May 200
Suzaku Observations of M82 X-1 : Detection of a Curved Hard X-ray Spectrum
A report is presented on Suzaku observations of the ultra-luminous X-ray
source X-1 in the starburst galaxy M82, made three time in 2005 October for an
exposure of ~ 30 ks each. The XIS signals from a region of radius 3 around the
nucleus defined a 2-10 keV flux of 2.1 x 10^-11 erg s-1 cm-2 attributable to
point sources. The 3.2-10 keV spectrum was slightly more convex than a
power-law with a photon index of 1.7. In all observations, the HXD also
detected signals from M82 up to ~ 20 keV, at a 12-20 keV flux of 4.4 x 10^-12
erg s-1 cm-2 . The HXD spectrum was steeper than that of the XIS. The XIS and
HXD spectra can be jointly reproduced by a cutoff power-law model, or similar
curved models. Of the detected wide-band signals, 1/3 to 2/3 are attributable
to X-1, while the remainder to other discrete sources in M82. Regardless of the
modeling of these contaminants, the spectrum attributable to X-1 is more curved
than a power-law, with a bolometric luminosity of (1.5 -3) x 10 ^40 erg s-1.
These results are interpreted as Comptonized emission from a black hole of
100-200 solar masses, radiating roughly at the Eddington luminosity.Comment: 19 pages, 9 figures, accepted in Publications of the Astronomical
Society of Japa
Discovery of Molecular Loop 3 in the Galactic Center: Evidence for a Positive-Velocity Magnetically Floated Loop towards
We have discovered a molecular dome-like feature towards and . The large velocity
dispersions of 50--100 km s of this feature are much larger than those
in the Galactic disk and indicate that the feature is located in the Galactic
center, probably within kpc of Sgr A. The distribution has a
projected length of pc and height of pc from the Galactic
disk and shows a large-scale monotonic velocity gradient of km s
per pc. The feature is also associated with HI gas having a
more continuous spatial and velocity distribution than that of CO. We
interpret the feature as a magnetically floated loop similar to loops 1 and 2
and name it "loop 3". Loop 3 is similar to loops 1 and 2 in its height and
length but is different from loops 1 and 2 in that the inner part of loop 3 is
filled with molecular emission. We have identified two foot points at the both
ends of loop 3. HI, CO and CO datasets were used to estimate the
total mass and kinetic energy of loop 3 to be \sim3.0 \times 10^{6} \Mo and
ergs. The huge size, velocity dispersions and energy
are consistent with the magnetic origin the Parker instability as in case of
loops 1 and 2 but is difficult to be explained by multiple stellar explosions.
We argue that loop 3 is in an earlier evolutionary phase than loops 1 and 2
based on the inner-filled morphology and the relative weakness of the foot
points. This discovery indicates that the western part of the nuclear gas disk
of kpc radius is dominated by the three well-developed magnetically
floated loops and suggests that the dynamics of the nuclear gas disk is
strongly affected by the magnetic instabilities.Comment: 30 pages, 10 figures. High resolution figures are available at
http://www.a.phys.nagoya-u.ac.jp/~motosuji/fujishita09_figs
A Detailed Observational Study of Molecular Loops 1 and 2 in the Galactic Center
Fukui et al. (2006) discovered two huge molecular loops in the Galactic
center located in (l, b) ~ (355 deg-359 deg, 0 deg-2 deg) in a large velocity
range of -180-40 km s^-1. Following the discovery, we present detailed
observational properties of the two loops based on NANTEN 12CO(J=1-0) and
13CO(J=1-0) datasets at 10 pc resolution including a complete set of velocity
channel distributions and comparisons with HI and dust emissions as well as
with the other broad molecular features. We find new features on smaller scales
in the loops including helical distributions in the loop tops and vertical
spurs. The loops have counterparts of the HI gas indicating that the loops
include atomic gas. The IRAS far infrared emission is also associated with the
loops and was used to derive an X-factor of 0.7(+/-0.1){\times}10^20 cm^-2 (K
km s^-1)^-1 to convert the 12CO intensity into the total molecular hydrogen
column density. From the 12CO, 13CO, H I and dust datasets we estimated the
total mass of loops 1 and 2 to be ~1.4 {\times} 106 Msun and ~1.9 {\times} 10^6
Msun, respectively, where the H I mass corresponds to ~10-20% of the total mass
and the total kinetic energy of the two loops to be ~10^52 ergs. An analysis of
the kinematics of the loops yields that the loops are rotating at ~47 km s-1
and expanding at ~141 km s^-1 at a radius of 670 pc from the center. Fukui et
al. (2006) presented a model that the loops are created by the magnetic
flotation due to the Parker instability with an estimated magnetic field
strength of ~150 {\mu}G. We present comparisons with the recent numerical
simulations of the magnetized nuclear disk by Machida et al. (2009) and
Takahashi et al. (2009) and show that the theoretical results are in good
agreements with the observations. The helical distributions also suggest that
some magnetic instability plays a role similarly to the solar helical features.Comment: 40 pages, 22 figures, submitted to publication in PAS
Discovery of Spectral Transitions from Two Ultra-Luminous Compact X-Ray Sources in Ic342
Two {\it ASCA} observations were made of two ultra-luminous compact X-ray
sources (ULXs), Source 1 and Source 2, in the spiral galaxy IC 342. In the 1993
observation, Source 2 showed a 0.5--10 keV luminosity of
ergs s (assuming a distance of 4.0 Mpc), and a hard power-law spectrum
of photon index . As already reported, Source 1 was times
brighter on that occasion, and exhibited a soft spectrum represented by a
multi-color disk model of inner-disk temperature keV. The second
observation made in February 2000 revealed that Source 1 had made a transition
into a hard spectral state, while Source 2 into a soft spectral state. The ULXs
are therefore inferred to exhibit two distinct spectral states, and sometimes
make transitions between them. These results significantly reinforce the
scenario which describes ULXs as mass-accreting black holes.Comment: 11 pages, 3 figures; acceoted for ApJ
Pilot VLBI Survey of SiO v=3 J=1--0 Maser Emission around Evolved Stars
In this Letter, we report detections of SiO v=3 J=1--0 maser emission in very
long baseline interferometric (VLBI) observations towards 4 out of 12
long-period variable stars: WX Psc, R Leo, W Hya, and T Cep. The detections
towards WX Psc and T Cep are new ones. We also present successful astrometric
observations of SiO v=2 and v=3 J=1--0 maser emissions associated with two
stars: WX Psc and W Hya and their position-reference continuum sources:
J010746.0+131205 and J135146.8-291218 with the VLBI Exploration of Radio
Astrometry (VERA). The relative coordinates of the position-reference continuum
source and SiO v=3 maser spots were measured with respect to those of an SiO
v=2 maser spot adopted as fringe-phase reference. Thus the faint continuum
sources were inversely phase-referenced to the bright maser sources. It implies
possible registration of multiple SiO maser line maps onto a common coordinate
system with 10 microarcsecond-level accuracy.Comment: 5 Pages, 3 figures, Fig.3 and Tab. 2 were corrected; Publications of
the Astronomical Society of Japan, Vol. 64, No. 6 issued on 2012 December 2
High Excitation Molecular Gas in the Galactic Center Loops; 12CO(J =2-1 and J =3-2) Observations
We have carried out 12CO(J =2-1) and 12CO(J =3-2) observations at spatial
resolutions of 1.0-3.8 pc toward the entirety of loops 1 and 2 and part of loop
3 in the Galactic center with NANTEN2 and ASTE. These new results revealed
detailed distributions of the molecular gas and the line intensity ratio of the
two transitions, R3-2/2-1. In the three loops, R3-2/2-1 is in a range from 0.1
to 2.5 with a peak at ~ 0.7 while that in the disk molecular gas is in a range
from 0.1 to 1.2 with a peak at 0.4. This supports that the loops are more
highly excited than the disk molecular gas. An LVG analysis of three
transitions, 12CO J =3-2 and 2-1 and 13CO J =2-1, toward six positions in loops
1 and 2 shows density and temperature are in a range 102.2 - 104.7 cm-3 and
15-100 K or higher, respectively. Three regions extended by 50-100 pc in the
loops tend to have higher excitation conditions as characterized by R3-2/2-1
greater than 1.2. The highest ratio of 2.5 is found in the most developed foot
points between loops 1 and 2. This is interpreted that the foot points indicate
strongly shocked conditions as inferred from their large linewidths of 50-100
km s-1, confirming the suggestion by Torii et al. (2010b). The other two
regions outside the foot points suggest that the molecular gas is heated up by
some additional heating mechanisms possibly including magnetic reconnection. A
detailed analysis of four foot points have shown a U shape, an L shape or a
mirrored-L shape in the b-v distribution. It is shown that a simple kinematical
model which incorporates global rotation and expansion of the loops is able to
explain these characteristic shapes.Comment: 59 pages, accepted to PAS
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