365 research outputs found
A search for energy-dependence of the Kes 73/1E 1841-045 morphology in GeV
While the Kes 73/1E 1841-045 system had been confirmed as an extended GeV
source, whether its morphology depends on the photon energy or not deserves our
further investigation. Adopting data collected by Fermi Large Area Telescope
(LAT) again, we look into the extensions of this source in three energy bands
individually: 0.3-1 GeV, 1-3 GeV and 3-200 GeV. We find that the 0.3-1 GeV
morphology is point-like and is quite different from those in the other two
bands, although we cannot robustly reject a unified morphology for the whole
LAT band.Comment: Approved for publication in PoS as a proceeding of the 7th
International Fermi Symposium (IFS2017
Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV
Context: The Crab pulsar and its nebula are the origin of relativistic
electrons which can be observed through their synchrotron and inverse Compton
emission. The transition between synchrotron-dominated and
inverse-Compton-dominated emissions takes place at eV. Aims: The
short-term (weeks to months) flux variability of the synchrotron emission from
the most energetic electrons is investigated with data from ten years of
observations with the Fermi Large Area Telescope (LAT) in the energy range from
60 MeV to 600 MeV. Methods: The off-pulse light-curve has been reconstructed
from phase-resolved data. The corresponding histogram of flux measurements is
used to identify distributions of flux-states and the statistical significance
of a lower-flux component is estimated with dedicated simulations of mock
light-curves. The energy spectra for different flux states are reconstructed.
Results: We confirm the presence of flaring-states which follow a log-normal
flux distribution. Additionally, we discover a low-flux state where the flux
drops to as low as 18.4% of the intermediate-state average flux and stays there
for several weeks. The transition time is observed to be as short as 2 days.
The energy spectrum during the low-flux state resembles the extrapolation of
the inverse-Compton spectrum measured at energies beyond several GeV energy,
implying that the high-energy part of the synchrotron emission is dramatically
depressed. Conclusions: The low-flux state found here and the transition time
of at most 10 days indicate that the bulk (%) of the synchrotron emission
above eV originates in a compact volume with apparent angular size of
. We tentatively infer that
the so-called inner knot feature is the origin of the bulk of the -ray
emission.Comment: Accepted by A&A on 05.05.2020; Original version submitted on
19.09.201
Inferring the origins of the pulsed gamma-ray emission from the Crab pulsar with 10-year Fermi LAT data
Context: The Crab pulsar is a bright -ray source detected at photon
energies up to 1 TeV. Its phase-averaged and phase-resolved -ray
spectra below 10 GeV exhibit exponential cutoffs while those above 10 GeV
apparently follow simple power-laws. Aims: We re-visit the -ray
properties of the Crab pulsar with 10-year \emph{Fermi} Large Area Telescope
(LAT) data in the range of 60 MeV--500 GeV. With the phase-resolved spectra, we
investigate the origins and mechanisms responsible for the emissions. Methods:
The phaseograms are reconstructed for different energy bands and further
analysed using a wavelet decomposition. The phase-resolved energy spectra are
combined with the observations of ground-based instruments like MAGIC and
VERITAS to achieve a larger energy converage. We fit power-law models to the
overlapping energy spectra from 10 GeV to 1 TeV. We include in the fit a
relative cross-calibration of energy scales between air-shower based gamma-ray
telescopes with the orbital pair-production telescope of the Fermi mission.
Results: We confirm the energy-dependence of the -ray pulse shape, and
equivalently, the phase-dependence of the spectral shape for the Crab pulsar. A
relatively sharp cutoff at a relatively high energy of 8 GeV is observed
for the bridge-phase emission. The 10 GeV spectrum observed for the second
pulse peak is harder than those for other phases. Conclusions: In view of the
diversity of phase-resolved spectral shapes of the Crab pulsar, we tentatively
propose a multi-origin scenario where the polar-cap, outer-gap and
relativistic-wind regions are involved.Comment: Original article published in A&A on 10.08.2020; Data values
available at CDS via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A43 ;
Erratum (at the back) accepted by A&A on 10.03.2021; Sincere gratitude is
given to D. Horns for his encouragement regarding my submission as a single
autho
Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
Either bulk rotation or local turbulence is widely invoked to drive
fragmentation in collapsing cores so as to produce multiple star systems. Even
when the two mechanisms predict different manners in which the stellar spins
and orbits are aligned, subsequent internal or external interactions can drive
multiple systems towards or away from alignment thus masking their formation
process. Here, we demonstrate that the geometrical and dynamical relationship
between the binary system and its surrounding bulk envelope provide the crucial
distinction between fragmentation models. We find that the circumstellar disks
of the binary protostellar system L1551 IRS 5 are closely parallel not just
with each other but also with their surrounding flattened envelope.
Measurements of the relative proper motion of the binary components spanning
nearly 30 yr indicate an orbital motion in the same sense as the envelope
rotation. Eliminating orbital solutions whereby the circumstellar disks would
be tidally truncated to sizes smaller than are observed, the remaining
solutions favor a circular or low-eccentricity orbit tilted by up to
25 from the circumstellar disks. Turbulence-driven fragmentation
can generate local angular momentum to produce a coplanar binary system, but
which bears no particular relationship with its surrounding envelope. Instead,
the observed properties conform with predictions for rotationally-driven
fragmentation. If the fragments were produced at different heights or on
opposite sides of the midplane in the flattened central region of a rotating
core, the resulting protostars would then exhibit circumstellar disks parallel
with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap
Multiwavelength studies of G298.60.0: An old GeV supernova remnant interacting with molecular clouds
Hadronic -ray sources associated with supernova remnants (SNRs) can
serve as stopwatches for the escape of cosmic rays from SNRs, which gradually
develops from highest-energy particles to lowest-energy particles with time. In
this work, we analyze the 13.7~yr \emph{Fermi}-LAT data to investigate the
-ray feature in/around the SNR G298.60.0 region. With -ray
spatial analyses, we detect three point-like components. Among them, Src-NE is
at the eastern SNR shell, and Src-NW is adjacent to the western edge of this
SNR. Src-NE and Src-NW demonstrate spectral breaks at energies around/below
1.8~GeV, suggesting an old SNR age of 10~kyr. We also look into the X-ray
emission from the G298.60.0 region, with the Chandra-ACIS data. We detected
an extended keV source having a centrally filled structure inside the radio
shell. The X-ray spectra are well fit by a model which assumes a collisional
ionisation equilibrium of the thermal plasma, further supporting an old SNR
age. Based on our analyses of the NANTEN CO- and ATCA-Parkes HI-line data, we
determined a kinematic distance of 10.1~kpc from us to G298.60.0. This
distance entails a large physical radius of the SNR of 15.5~pc, which is
an additional evidence for an old age of 10~kyr. Besides, the CO data cube
enables us to three-dimensionally locate the molecular clouds (MCs) which are
potentially interacting with SNR G298.60.0 and could account for the
hadronic -rays detected at Src-NE or Src-NW. Furthermore, the
multiwavelength observational properties unanimously imply that the SNR--MC
interaction occurs mainly in the northeast direction.Comment: Accepted by Publications of the Astronomical Society of Japan (PASJ)
on 16-Jan-202
Genetic study of congenital bile-duct dilatation identifies de novo and inherited variants in functionally related genes
Background:
Congenital dilatation of the bile-duct (CDD) is a rare, mostly sporadic, disorder that results in bile retention with severe associated complications. CDD affects mainly Asians. To our knowledge, no genetic study has ever been conducted.
Methods:
We aim to identify genetic risk factors by a “trio-based” exome-sequencing approach, whereby 31 CDD probands and their unaffected parents were exome-sequenced. Seven-hundred controls from the local population were used to detect gene-sets significantly enriched with rare variants in CDD patients.
Results:
Twenty-one predicted damaging de novo variants (DNVs; 4 protein truncating and 17 missense) were identified in several evolutionarily constrained genes (p < 0.01). Six genes carrying DNVs were associated with human developmental disorders involving epithelial, connective or bone morphologies (PXDN, RTEL1, ANKRD11, MAP2K1, CYLD, ACAN) and four linked with cholangio- and hepatocellular carcinomas (PIK3CA, TLN1 CYLD, MAP2K1). Importantly, CDD patients have an excess of DNVs in cancer-related genes (p < 0.025). Thirteen genes were recurrently mutated at different sites, forming compound heterozygotes or functionally related complexes within patients.
Conclusions:
Our data supports a strong genetic basis for CDD and show that CDD is not only genetically heterogeneous but also non-monogenic, requiring mutations in more than one genes for the disease to develop. The data is consistent with the rarity and sporadic presentation of CDD
Spinodal Decomposition in a Binary Polymer Mixture: Dynamic Self Consistent Field Theory and Monte Carlo Simulations
We investigate how the dynamics of a single chain influences the kinetics of
early stage phase separation in a symmetric binary polymer mixture. We consider
quenches from the disordered phase into the region of spinodal instability. On
a mean field level we approach this problem with two methods: a dynamical
extension of the self consistent field theory for Gaussian chains, with the
density variables evolving in time, and the method of the external potential
dynamics where the effective external fields are propagated in time. Different
wave vector dependencies of the kinetic coefficient are taken into account.
These early stages of spinodal decomposition are also studied through Monte
Carlo simulations employing the bond fluctuation model that maps the chains --
in our case with 64 effective segments -- on a coarse grained lattice. The
results obtained through self consistent field calculations and Monte Carlo
simulations can be compared because the time, length, and temperature scales
are mapped onto each other through the diffusion constant, the chain extension,
and the energy of mixing. The quantitative comparison of the relaxation rate of
the global structure factor shows that a kinetic coefficient according to the
Rouse model gives a much better agreement than a local, i.e. wave vector
independent, kinetic factor. Including fluctuations in the self consistent
field calculations leads to a shorter time span of spinodal behaviour and a
reduction of the relaxation rate for smaller wave vectors and prevents the
relaxation rate from becoming negative for larger values of the wave vector.
This is also in agreement with the simulation results.Comment: Phys.Rev.E in prin
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