4,036 research outputs found
Flat Spectrum X-ray Emission from the Direction of a Molecular Cloud Associated with SNR RX J1713.7-3946
We report on the discovery of a hard X-ray source with ASCA from a molecular
cloud in the vicinity of the SNR RX J1713.7-3946. The energy spectrum (1--10
keV) shows a flat continuum which is described by a power-law with photon index
1.0 +-0.4. We argue that this unusually flat spectrum can be best interpreted
in terms of characteristic bremsstrahlung emission from the
ionization-loss-flattened distribution of either sub-relativistic protons or
mildly-relativistic electrons. The strong shock of the SNR RX J1713.7-3946,
which presumably interacts with the molecular cloud, as evidenced by
observations of CO-lines, seems to be a natural site of acceleration of such
sub- or mildly-relativistic nonthermal particles. However, the observed X-ray
luminosity of 1.7 10^35 erg/s (for 6 kpc distance) requires that a huge kinetic
energy of about 10^50 erg be released in the form of nonthermal particles to
illuminate the cloud. The shock-acceleration at RX J1713.7-3946 can barely
satisfy this energetic requirement, unless (i) the source is located much
closer than 6 kpc and/or (ii) the mechanical energy of the explosion
essentially exceeds 10^51 erg. Another possibility would be that an essential
part of the "lost" energy is somehow converted to plasma waves, which return
this energy to nonthermal particles through their turbulent reacceleration on
plasma waves. Irrespective of mechanisms responsible for production of
high-energy particles, the flat X-ray emission seems to be a signature of a new
striking energetic phenomenon in molecular clouds.Comment: 6 pages, 2 figures, Accepted for publication in PAS
Force measurements of a superconducting-film actuator for a cryogenic interferometric gravitational-wave detector
We measured forces applied by an actuator with a YBCO film at near 77 K for
the Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. An
actuator consisting of both a YBCO film of 1.6 micrometers thickness and 0.81
square centimeters area and a solenoid coil exerted a force of up to 0.2 mN on
a test mass. The presented actuator system can be used to displace the mirror
of LCGT for fringe lock of the interferometer.Comment: 9 pages, 3 figure
Chandra observations of the HII complex G5.89-0.39 and TeV gamma-ray source HESSJ1800-240B
We present the results of our investigation, using a Chandra X-ray
observation, into the stellar population of the massive star formation region
G5.89-0.39, and its potential connection to the coincident TeV gamma-ray source
HESSJ1800-240B. G5.89-0.39 comprises two separate HII regions G5.89-0.39A and
G5.89-0.39B (an ultra-compact HII region). We identified 159 individual X-ray
point sources in our observation using the source detection algorithm
\texttt{wavdetect}. 35 X-ray sources are associated with the HII complex
G5.89-0.39. The 35 X-ray sources represent an average unabsorbed luminosity
(0.3-10\,keV) of \,erg/s, typical of B7-B5 type stars. The
potential ionising source of G5.89-0.39B known as Feldt's star is possibly
identified in our observation with an unabsorbed X-ray luminosity suggestive of
a B7-B5 star. The stacked energy spectra of these sources is well-fitted with a
single thermal plasma APEC model with kT5\,keV, and column density
N\,cm (A). The residual
(source-subtracted) X-ray emission towards G5.89-0.39A and B is about 30\% and
25\% larger than their respective stacked source luminosities. Assuming this
residual emission is from unresolved stellar sources, the total
B-type-equivalent stellar content in G5.89-0.39A and B would be 75 stars,
consistent with an earlier estimate of the total stellar mass of hot stars in
G5.89-0.39. We have also looked at the variability of the 35 X-ray sources in
G5.89-0.39. Ten of these sources are flagged as being variable. Further studies
are needed to determine the exact causes of the variability, however the
variability could point towards pre-main sequence stars. Such a stellar
population could provide sufficient kinetic energy to account for a part of the
GeV to TeV gamma-ray emission in the source HESSJ1800-240B.Comment: 34 pages, 9 figure
Fine-structure in the nonthermal X-ray emission of SNR RX J1713.7-3946 revealed by Chandra
We present morphological and spectroscopic studies of the northwest rim of
the supernova remnant RX J1713.7-3946 based on observations by the Chandra
X-ray observatory. We found a complex network of nonthermal (synchrotron) X-ray
filaments, as well as a 'void' type structure -- a dim region of a circular
shape -- in the northwest rim. It is remarkable that despite distinct
brightness variations, the X-ray spectra everywhere in this region can be well
fitted with a power-law model with photon index around 2.3. We briefly discuss
some implications of these results and argue that the resolved X-ray features
in the northwest rim may challenge the perceptions of standard (diffusive
shock-acceleration) models concerning the production, propagation and radiation
of relativistic particles in supernova remnants.Comment: 8 pages, 9 figures; accepted for publication in A&A; significant
additions for publication in Main journal (previous version was for A&A
Letter); a manuscript (as a single PDF file, 501kb) including all figures is
available at http://www.astro.isas.ac.jp/~uchiyama/publication/h4106.pd
Synthesis and properties of bis(1,3-benzodithiole)-type redox systems containing a xylyl rotator unit: A new type of redox-responsive molecular rotor
A new type of redox-responsive molecular rotors (3(2+)/4) possessing a xylyl rotator unit have been designed and synthesized. Reduction of 3(2+) with zinc gave the corresponding cyclization products (4), from which dications (3 2,) were regenerated upon oxidation. Cyclic voltammetry also showed the interconversion between 3(2+) and 4. Variable-temperature (1)H NMR measurements revealed that the rotational barriers of the xylyl units in the neutral states (4) are higher than those in the dication states (3(2+)).ArticleHETEROCYCLES. 74: 251-257 (2007)journal articl
Constraints on cosmic-ray efficiency in the supernova remnant RCW 86 using multi-wavelength observations
Several young supernova remnants (SNRs) have recently been detected in the
high-energy and very-high-energy gamma-ray domains. As exemplified by RX
J1713.7-3946, the nature of this emission has been hotly debated, and direct
evidence for the efficient acceleration of cosmic-ray protons at the SNR shocks
still remains elusive. We analyzed more than 40 months of data acquired by the
Large Area Telescope (LAT) on-board the Fermi Gamma-Ray Space Telescope in the
HE domain, and gathered all of the relevant multi-wavelength (from radio to VHE
gamma-rays) information about the broadband nonthermal emission from RCW 86.
For this purpose, we re-analyzed the archival X-ray data from the ASCA/Gas
Imaging Spectrometer (GIS), the XMM-Newton/EPIC-MOS, and the RXTE/Proportional
Counter Array (PCA). Beyond the expected Galactic diffuse background, no
significant gamma-ray emission in the direction of RCW 86 is detected in any of
the 0.1-1, 1-10 and 10-100 GeV Fermi-LAT maps. In the hadronic scenario, the
derived HE upper limits together with the HESS measurements in the VHE domain
can only be accommodated by a spectral index Gamma <= 1.8, i.e. a value
in-between the standard (test-particle) index and the asymptotic limit of
theoretical particle spectra in the case of strongly modified shocks. The
interpretation of the gamma-ray emission by inverse Compton scattering of high
energy electrons reproduces the multi-wavelength data using a reasonable value
for the average magnetic field of 15-25 muG. For these two scenarios, we
assessed the level of acceleration efficiency. We discuss these results in the
light of existing estimates of the magnetic field strength, the effective
density and the acceleration efficiency in RCW 86.Comment: Accepted for publication in A&A; 10 pages and 4 figure
The Timing Counter of the MEG experiment: calibration and performance
The MEG detector is designed to test Lepton Flavor Violation in the
decay down to a Branching Ratio of a few
. The decay topology consists in the coincident emission of a
monochromatic photon in direction opposite to a monochromatic positron. A
precise measurement of the relative time is crucial to suppress
the background. The Timing Counter (TC) is designed to precisely measure the
time of arrival of the and to provide information to the trigger system.
It consists of two sectors up and down stream the decay target, each consisting
of two layers. The outer one made of scintillating bars and the inner one of
scintillating fibers. Their design criteria and performances are described.Comment: Presented at the 12th Topical Seminar on Innovative Particle and
Radiation Detectors (IPRD10) 7 - 10 June 2010, Siena. Accepted by Nuclear
Physics B (Proceedings Supplements) (2011)tal
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