2,619 research outputs found
Spin-relaxation anisotropy in a nanowire quantum dot with strong spin-orbit coupling
We study the impacts of the magnetic field direction on the spin-manipulation
and the spin-relaxation in a one-dimensional quantum dot with strong spin-orbit
coupling. The energy spectrum and the corresponding eigenfunctions in the
quantum dot are obtained exactly. We find that no matter how large the
spin-orbit coupling is, the electric-dipole spin transition rate as a function
of the magnetic field direction always has a periodicity. However, the
phonon-induced spin relaxation rate as a function of the magnetic field
direction has a periodicity only in the weak spin-orbit coupling regime,
and the periodicity is prolonged to in the strong spin-orbit coupling
regime.Comment: 8 pages, 4 figure
Fermi Large Area Telescope observations of the supernova remnant HESS J1731-347
Context: HESS J1731-347 has been identified as one of the few TeV-bright
shell-type supernova remnants (SNRs). These remnants are dominated by
nonthermal emission, and the nature of TeV emission has been continuously
debated for nearly a decade.
Aims: We carry out the detailed modeling of the radio to gamma-ray spectrum
of HESS J1731-347 to constrain the magnetic field and energetic particles
sources, which we compare with those of the other TeV-bright shell-type SNRs
explored before.
Methods: Four years of data from Fermi Large Area Telescope (LAT)
observations for regions around this remnant are analyzed, leading to no
detection correlated with the source discovered in the TeV band. The Markov
Chain Monte Carlo method is used to constrain parameters of one-zone models for
the overall emission spectrum.
Results: Based on the 99.9% upper limits of fluxes in the GeV range, one-zone
hadronic models with an energetic proton spectral slope greater than 1.8 can be
ruled out, which favors a leptonic origin for the gamma-ray emission, making
this remnant a sibling of the brightest TeV SNR RX J1713.7-3946, the Vela
Junior SNR RX J0852.0-4622, and RCW 86. The best-fit leptonic model has an
electron spectral slope of 1.8 and a magnetic field of about 30 muG, which is
at least a factor of 2 higher than those of RX J1713.7-3946 and RX
J0852.0-4622, posing a challenge to the distance estimate and/or the energy
equipartition between energetic electrons and the magnetic field of this
source. A measurement of the shock speed will address this challenge and has
implications on the magnetic field evolution and electron acceleration driven
by shocks of SNRs.Comment: 7 pages, 3 fogures, A&A in pres
Tradeoffs Between Transmission Intervals and Delays for Decentralized Networked Control Systems Based on a Gain Assignment Approach
Low expression of PTK6/Brk predicts poor prognosis in patients with laryngeal squamous cell carcinoma
The energy distribution of relativistic electrons in the kilo-parsec scale jet of M87 with Chandra
The X-ray emission from the jets in Active Galactic Nuclei (AGN) carries
important information on the distributions of relativistic electrons and
magnetic fields on large scales. We reanalyze archival Chandra observations on
the jet of M87 from 2000 to 2016 with a total exposure of 1460 kiloseconds to
explore the X-ray emission characteristics along the jet. We investigate the
variability behaviours of the nucleus and the inner jet component HST-1, and
confirm indications for day-scale X-ray variability in the nucleus
contemporaneous to the 2010 high TeV gamma-ray state. HST-1 shows a general
decline in X-ray flux over the last few years consistent with its synchrotron
interpretation. We extract the X-ray spectra for the nucleus and all knots in
the jet, showing that they are compatible with a single power-law within the
X-ray band. There are indications of the resultant X-ray photon index to
exhibit a trend, with slight but significant index variations ranging from
(e.g. in knot D) to (in the outer knots F, A, and
B). When viewed in a multi-wavelength context, a more complex situation is
arising. Fitting the radio to X-ray spectral energy distributions (SEDs)
assuming a synchrotron origin, we show that a broken power-law electron
spectrum with break energy around TeV allows a
satisfactorily description of the multi-band SEDs for most of the knots.
However, in the case of knots B, C and D we find indications that an additional
high energy component is needed to adequately reproduce the broadband SEDs. We
discuss the implications and suggest that a stratified jet model may account
for the differences.Comment: accepted for publication in A&
Tentative evidence of spatially extended GeV emission from SS433/W50
We analyze 10 years of Fermi-LAT data towards the SS433/W50 region. With the
latest source catalog and diffuse background models, the gamma-ray excess from
SS433/W50 is detected with a significance of 6{\sigma} in the photon energy
range of 500 MeV - 10 GeV. Our analysis indicates that an extended flat disk
morphology is preferred over a point-source description, suggesting that the
GeV emission region is much larger than that of the TeV emission detected by
HAWC. The size of the GeV emission is instead consistent with the extent of the
radio nebula W50, a supernova remnant being distorted by the jets, so we
suggest that the GeV emission may originate from this supernova remnant. The
spectral result of the GeV emission is also consistent with an supernova
remnant origin. We also derive the GeV flux upper limits on the TeV emission
region, which put moderate constrains on the leptonic models to explain the
multiwavelength data.Comment: 7 pages, 4 figures, accepted for publication in A&
New estimation of the nuclear de-excitation line emission from the supernova remnant Cassiopeia A
MeV nuclear de-excitation lines serve as a unique tool to study low-energy
cosmic rays (CRs), containing both spectral and elemental information of the
interacting material. In this paper, we estimated the possible nuclear
de-excitation lines from the young supernova remnant Cassiopeia A. Given
different CR spectral shapes and interacting materials, we found the predicted
fluxes of strong narrow line emissions from the remnant are highly
model-dependent, ranging from about
to for the 4.44 MeV narrow line and
from about to for the 6.13 MeV narrow line, respectively. Based on the
new estimation, we also discussed the detection probability of these line
emissions against the MeV diffuse Galactic background under different
assumptions of instrument response functions.Comment: 6 pages, 6 figures, accepted for publication in MNRA
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