3,312 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
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
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
Pulse Control of Decoherence in a Qubit Coupled with a Quantum Environment
We study the time evolution of a qubit linearly coupled with a quantum
environment under a sequence of short pi pulses. Our attention is focused on
the case where qubit-environment interactions induce the decoherence with
population decay. We assume that the environment consists of a set of bosonic
excitations. The time evolution of the reduced density matrix for the qubit is
calculated in the presence of periodic short pi pulses. We confirm that the
decoherence is suppressed if the pulse interval is shorter than the correlation
time for qubit-environment interactions.Comment: 5 pages, 2figure
Design and test of an extremely high resolution Timing Counter for the MEG II experiment: preliminary results
The design and tests of Timing Counter elements for the upgrade of the MEG
experiment, MEG II,is presented. The detector is based on several small plates
of scintillator with a Silicon PhotoMultipliers dual-side readout. The
optimisation of the single counter elements (SiPMs, scintillators, geometry) is
described. Moreover, the results obtained with a first prototype tested at the
Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati (LNF) are
presented.Comment: 10 pages, 7 figures. Presented at the 13th Topical Seminar on
Innovative Particle and Radiation Detectors (IPRD13) 7-10 October 2013 Siena,
Ital
A chi-squared time-frequency discriminator for gravitational wave detection
Searches for known waveforms in gravitational wave detector data are often
done using matched filtering. When used on real instrumental data, matched
filtering often does not perform as well as might be expected, because
non-stationary and non-Gaussian detector noise produces large spurious filter
outputs (events). This paper describes a chi-squared time-frequency test which
is one way to discriminate such spurious events from the events that would be
produced by genuine signals. The method works well only for broad-band signals.
The case where the filter template does not exactly match the signal waveform
is also considered, and upper bounds are found for the expected value of
chi-squared.Comment: 18 pages, five figures, RevTex
X-ray observations of PSR B1259â63 near the 2007 periastron passage
PSR B1259â63 is a 48-ms radio pulsar in a highly eccentric 3.4-yr orbit with a Be star SS 2883. Unpulsed Îł-ray, X-ray and radio emission components are observed from the binary system. It is likely that the collision of the pulsar wind with the anisotropic wind of the Be star plays a crucial role in the generation of the observed non-thermal emission. The 2007 periastron passage was observed in unprecedented details with Suzaku, Swift, XMM-Newton and Chandra missions. We present here the results of this campaign and compare them with previous observations. With these data we are able, for the first time, to study the details of the spectral evolution of the source over a 2-month period of the passage of the pulsar close to the Be star. New data confirm the pre-periastron spectral hardening, with the photon index reaching a value smaller than 1.5, observed during a local flux minimum. If the observed X-ray emission is due to the inverse Compton (IC) losses of the 10-MeV electrons, then such a hard spectrum can be a result of Coulomb losses, or can be related to the existence of the low-energy cut-off in the electron spectrum. Alternatively, if the X-ray emission is a synchrotron emission of very high-energy electrons, the observed hard spectrum can be explained if the high-energy electrons are cooled by IC emission in Klein-Nishina regime. Unfortunately, the lack of simultaneous data in the TeV energy band prevents us from making a definite conclusion on the nature of the observed spectral hardening and, therefore, on the origin of the X-ray emissio
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