9,649 research outputs found
A NuSTAR Observation of the Gamma-ray Emitting Millisecond Pulsar PSR J1723-2837
We report on the first NuSTAR observation of the gamma-ray emitting
millisecond pulsar binary PSR J1723-2837. X-ray radiation up to 79 keV is
clearly detected and the simultaneous NuSTAR and Swift spectrum is well
described by an absorbed power-law with a photon index of ~1.3. We also find
X-ray modulations in the 3-10 keV, 10-20 keV, 20-79 keV, and 3-79 keV bands at
the 14.8-hr binary orbital period. All these are entirely consistent with
previous X-ray observations below 10 keV. This new hard X-ray observation of
PSR J1723-2837 provides strong evidence that the X-rays are from the
intrabinary shock via an interaction between the pulsar wind and the outflow
from the companion star. We discuss how the NuSTAR observation constrains the
physical parameters of the intrabinary shock model.Comment: Accepted for publication in ApJ. 5 pages, 3 figure
Swift, XMM-Newton, and NuSTAR observations of PSR J2032+4127/MT91 213
We report our recent Swift, NuSTAR, and XMM-Newton X-ray and Lijiang optical
observations on PSR J2032+4127/MT91 213, the gamma-ray binary candidate with a
period of 45-50 years. The coming periastron of the system was predicted to be
in November 2017, around which high-energy flares from keV to TeV are expected.
Recent studies with Chandra and Swift X-ray observations taken in 2015/16
showed that its X-ray emission has been brighter by a factors of ~10 than that
before 2013, probably revealing some on-going activities between the pulsar
wind and the stellar wind. Our new Swift/XRT lightcurve shows no strong
evidence of a single vigorous brightening trend, but rather several strong
X-ray flares on weekly to monthly timescales with a slowly brightening
baseline, namely the low state. The NuSTAR and XMM-Newton observations taken
during the flaring and the low states, respectively, show a denser environment
and a softer power-law index during the flaring state, implying that the pulsar
wind interacted with stronger stellar winds of the companion to produce the
flares. These precursors would be crucial in studying the predicted giant
outburst from this extreme gamma-ray binary during the periastron passage in
late 2017.Comment: 6 pages, including 3 figures and 2 tables. Accepted for publication
in Ap
Remaining missed opportunities of child survival in Peru:Modelling mortality impact of universal and equitable coverage of proven interventions
Abstract Background Peru has made great improvements in reducing stunting and child mortality in the past decade, and has reached the Millennium Development Goals 1 and 4. The remaining challenges or missed opportunities for child survival needs to be identified and quantified, in order to guide the next steps to further improve child survival in Peru. Methods We used the Lives Saved Tool (LiST) to project the mortality impact of proven interventions reaching every women and child in need, and the mortality impact of eliminating inequalities in coverage distribution between wealth quintiles and urban–rural residence. Results Our analyses quantified the remaining missed opportunities in Peru, where prioritizing scale-up of facility-based case management for all small and sick babies will be most effective in mortality reduction, compared to other evidenced-based interventions that prevent maternal and child deaths. Eliminating coverage disparities between the poorest quintiles and the richest will reduce under-five and neonatal mortality by 22.0 and 40.6 %, while eliminating coverage disparities between those living in rural and urban areas will reduce under-five and neonatal mortality by 29.3 and 45.2 %. This projected neonatal mortality reduction achieved by eliminating coverage disparities is almost comparable to that already achieved by Peru over the past decade. Conclusions Although Peru has made great strides in improving child survival, further improvement in child health, especially in newborn health can be achieved if there is universal and equitable coverage of proven, quality health facility-based interventions. The magnitude of reduction in mortality will be similar to what has been achieved in the past decade. Strengthening health system to identify, understand, and direct resources to the poor and rural areas will ensure that Peru achieve the Sustainable Development Goals by 2030
NuSTAR observations and broadband spectral energy distribution modeling of the millisecond pulsar binary PSR J1023+0038
We report the first hard X-ray (3-79 keV) observations of the millisecond
pulsar (MSP) binary PSR J1023+0038 using NuSTAR. This system has been shown
transiting between a low-mass X-ray binary (LMXB) state and a rotation-powered
MSP state. The NuSTAR observations were taken in both LMXB state and
rotation-powered state. The source is clearly seen in both states up to ~79
keV. During the LMXB state, the 3-79 keV flux is about a factor of 10 higher
that in the rotation-powered state. The hard X-rays show clear orbital
modulation during the X-ray faint rotation-powered state but the X-ray orbital
period is not detected in the X-ray bright LMXB state. In addition, the X-ray
spectrum changes from a flat power-law spectrum during the rotation-powered
state to a steeper power-law spectrum in the LMXB state. We suggest that the
hard X-rays are due to the intra-binary shock from the interaction between the
pulsar wind and the injected material from the low-mass companion star. During
the rotation-powered MSP state, the X-ray orbital modulation is due to Doppler
boosting of the shocked pulsar wind. At the LMXB state, the evaporating matter
of the accretion disk due to the gamma-ray irradiation from the pulsar stops
almost all the pulsar wind, resulting the disappearance of the X-ray orbital
modulation.Comment: 8 pages, 6 figures; accepted for publication in Ap
Vortices and the entrainment transition in the 2D Kuramoto model
We study synchronization in the two-dimensional lattice of coupled phase
oscillators with random intrinsic frequencies. When the coupling is larger
than a threshold , there is a macroscopic cluster of
frequency-synchronized oscillators. We explain why the macroscopic cluster
disappears at . We view the system in terms of vortices, since cluster
boundaries are delineated by the motion of these topological defects. In the
entrained phase (), vortices move in fixed paths around clusters, while
in the unentrained phase (), vortices sometimes wander off. These
deviant vortices are responsible for the disappearance of the macroscopic
cluster. The regularity of vortex motion is determined by whether clusters
behave as single effective oscillators. The unentrained phase is also
characterized by time-dependent cluster structure and the presence of chaos.
Thus, the entrainment transition is actually an order-chaos transition. We
present an analytical argument for the scaling for small
lattices, where is the threshold for phase-locking. By also deriving the
scaling , we thus show that for small , in
agreement with numerics. In addition, we show how to use the linearized model
to predict where vortices are generated.Comment: 11 pages, 8 figure
High-Energy emissions from the Pulsar/Be binary system PSR J2032+4127/MT91 213
PSR J2032+4127 is a radio-loud gamma-ray-emitting pulsar; it is orbiting
around a high-mass Be type star with a very long orbital period of 25-50years,
and is approaching periastron, which will occur in late 2017/early 2018. This
system comprises with a young pulsar and a Be type star, which is similar to
the so-called gamma-ray binary PSR~B1259-63/LS2883. It is expected therefore
that PSR J2032+4127 shows an enhancement of high-energy emission caused by the
interaction between the pulsar wind and Be wind/disk around periastron. Ho et
al. recently reported a rapid increase in the X-ray flux from this system. In
this paper, we also confirm a rapid increase in the X-ray flux along the orbit,
while the GeV flux shows no significant change. We discuss the high-energy
emissions from the shock caused by the pulsar wind and stellar wind interaction
and examine the properties of the pulsar wind in this binary system. We argue
that the rate of increase of the X-ray flux observed by Swift indicates (1) a
variation of the momentum ratio of the two-wind interaction region along the
orbit, or (2) an evolution of the magnetization parameter of the pulsar wind
with the radial distance from the pulsar. We also discuss the pulsar wind/Be
disk interaction at the periastron passage, and propose the possibility of
formation of an accretion disk around the pulsar. We model high-energy
emissions through the inverse-Compton scattering process of the
cold-relativistic pulsar wind off soft photons from the accretion disk.Comment: 18 pages, 23 figures, 1 Table, accepted for publication in Ap
The X-ray modulation of PSR J2032+4127/MT91 213 during the Periastron Passage in 2017
We present the Neil Gehrels Swift Observatory (Swift), Fermi Large Area
Telescope (Fermi-LAT), and Karl G. Jansky Very Large Array (VLA) observations
of the gamma-ray binary PSR J2032+4127/MT91 213, of which the periastron
passage has just occurred in November 2017. In the Swift X-ray light curve, the
flux was steadily increasing before mid-October 2017, however, a sharp X-ray
dip on a weekly time-scale is seen during the periastron passage, followed by a
post-periastron X-ray flare lasting for ~20 days. We suggest that the X-ray dip
is caused by (i) an increase of the magnetization parameter at the shock, and
(ii) the suppression due to the Doppler boosting effect. The 20-day
post-periastron flare could be a consequence of the Be stellar disk passage by
the pulsar. An orbital GeV modulation is also expected in our model, however,
no significant variability is seen in the Fermi-LAT light curve. We suspect
that the GeV emission resulted from the interaction between the binary's
members is hidden behind the bright magnetospheric emission of the pulsar.
Pulsar gating technique would be useful to remove the magnetospheric emission
and recover the predicted GeV modulation, if an accurate radio timing solution
over the periastron passage is provided in the future.Comment: 6 pages, including 2 figures. Accepted for publication in Ap
Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
Recent observations strongly suggest that the millisecond pulsar binary PSR
J1023+0038 has developed an accretion disk since 2013 June. We present a
multi-wavelength analysis of PSR J1023+0038, which reveals that 1) its
gamma-rays suddenly brightened within a few days in June/July 2013 and has
remained at a high gamma-ray state for several months; 2) both UV and X-ray
fluxes have increased by roughly an order of magnitude, and 3) the spectral
energy distribution has changed significantly after the gamma-ray sudden flux
change. Time variabilities associated with UV and X-rays are on the order of
100-500 seconds and 50-100 seconds, respectively. Our model suggests that a
newly formed accretion disk due to the sudden increase of the stellar wind
could explain the changes of all these observed features. The increase of UV is
emitted from the disk, and a new component in gamma-rays is produced by inverse
Compton scattering between the new UV component and pulsar wind. The increase
of X-rays results from the enhancement of injection pulsar wind energy into the
intra-binary shock due to the increase of the stellar wind. We also predict
that the radio pulses may be blocked by the evaporated winds from the disk and
the pulsar is still powered by rotation.Comment: 8 pages, 3 figures; accepted for publication in Ap
Critical factors affecting the quality of industrialized building system projects in China
2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcmaVersion of RecordPublishe
Discovery of an unidentified Fermi object as a black widow-like millisecond pulsar
The Fermi Gamma-ray Space Telescope has revolutionized our knowledge of the
gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray
pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the
outer-gap model predicts different sites of emission for the radio and
gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible
in the radio. Here we report the discovery of a "radio-quiet" gamma-ray
emitting MSP candidate by using Fermi, Chandra, Swift, and optical
observations. The X-ray and gamma-ray properties of the source are consistent
with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical
and X-ray data. We suggest that the source is a black widow-like MSP with a
~0.1 solar-mass late-type companion star. Based on the profile of the optical
and X-ray light-curves, the companion star is believed to be heated by the
pulsar while the X-ray emissions originate from pulsar magnetosphere and/or
from intra-binary shock. No radio detection of the source has been reported yet
and although no gamma-ray/radio pulsation has been found, we estimated that the
spin period of the MSP is ~3-5 ms based on the inferred gamma-ray luminosity.Comment: 6 pages, 2 figures; accepted for publication in ApJ
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