4,588 research outputs found
CXOU J160103.1-513353: another CCO with a carbon atmosphere?
We report on the analysis of XMM-Newton observations of the central compact
object CXOU J160103.1-513353 located in the center of the non-thermally
emitting supernova remnant (SNR) G330.2+1.0. The X-ray spectrum of the source
is well described with either single-component carbon or two-component hydrogen
atmosphere models. In the latter case, the observed spectrum is dominated by
the emission from a hot component with a temperature ~3.9MK, corresponding to
the emission from a hotspot occupying ~1% of the stellar surface (assuming a
neutron star with mass M = 1.5M, radius of 12 km, and distance of ~5
kpc as determined for the SNR). The statistics of the spectra and obtained
upper limits on the pulsation amplitude expected for a rotating neutron star
with hot spots do not allow us to unambiguously distinguish between these two
scenarios. We discuss, however, that while the non-detection of the pulsations
can be explained by the unfortunate orientation in CXOU J160103.1-513353, this
is not the case when the entire sample of similar objects is considered. We
therefore conclude that the carbon atmosphere scenario is more plausible.Comment: accepted in A&
Searching for coherent pulsations in ultraluminous X-ray sources
Luminosities of ultraluminous X-ray sources (ULXs) are uncomfortably large if
compared to the Eddington limit for isotropic accretion onto stellar-mass
object. Most often either supercritical accretion onto stellar mass black hole
or accretion onto intermediate mass black holes is invoked the high
luminosities of ULXs. However, the recent discovery of coherent pulsations from
M82 ULX with NuSTAR showed that another scenario implying accretion onto a
magnetized neutron star is possible for ULXs. Motivated by this discovery, we
re-visited the available XMM-Newton archival observations of several bright
ULXs with a targeted search for pulsations to check whether accreting neutron
stars might power other ULXs as well. We have found no evidence for significant
coherent pulsations in any of the sources including the M82 ULX. We provide
upper limits for the amplitude of possibly undetected pulsed signal for the
sources in the sample.Comment: 2 pages, 1 figure, submitted to A&
Orbital parameters of V 0332+53 from 2015 giant outburst data
We present the updated orbital solution for the transient Be X-ray binary V
0332+53 comple- menting historical measurements with the data from the
gamma-ray burst monitor onboard Fermi obtained during the outburst in
June-October 2015. We model the observed changes in the spin- frequency of the
pulsar and deduce the orbital parameters of the system. We significantly
improve existing constrains and show that contrary to the previous findings no
change in orbital parameters is required to explain the spin evolution of the
source during the outbursts in 1983, 2005 and 2015. The reconstructed intrinsic
spin-up of the neutron star during the latest outburst is found to be
comparable with previosly observed values and predictions of the accretion
torque theory.Comment: 3 pages, 2 figures, submitted to A&
The shape and mechanics of curved fold origami structures
We develop recursion equations to describe the three-dimensional shape of a
sheet upon which a series of concentric curved folds have been inscribed. In
the case of no stretching outside the fold, the three-dimensional shape of a
single fold prescribes the shape of the entire origami structure. To better
explore these structures, we derive continuum equations, valid in the limit of
vanishing spacing between folds, to describe the smooth surface intersecting
all the mountain folds. We find that this surface has negative Gaussian
curvature with magnitude equal to the square of the fold's torsion. A series of
open folds with constant fold angle generate a helicoid
Self-Assembly on a Cylinder: A Model System for Understanding the Constraint of Commensurability
A crystal lattice, when confined to the surface of a cylinder, must have a
periodic structure that is commensurate with the cylinder circumference. This
constraint can frustrate the system, leading to oblique crystal lattices or to
structures with a chiral seam known as a "line slip" phase, neither of which
are stable for isotropic particles in equilibrium on flat surfaces. In this
study, we use molecular dynamics simulations to find the steady-state structure
of spherical particles with short-range repulsion and long-range attraction far
below the melting temperature. We vary the range of attraction using the
Lennard-Jones and Morse potentials and find that a shorter-range attraction
favors the line-slip. We develop a simple model based only on geometry and bond
energy to predict when the crystal or line-slip phases should appear, and find
reasonable agreement with the simulations. The simplicity of this model allows
us to understand the influence of the commensurability constraint, an
understanding that might be extended into the more general problem of
self-assembling particles in strongly confined spaces.Comment: 12 pages, 9 figures. Submitted for publication, 201
Ten years of INTEGRAL observations of the hard X-ray emission from SGR 1900+14
We exploited the high sensitivity of the INTEGRAL IBIS/ISGRI instrument to
study the persistent hard X-ray emission of the soft gamma-ray repeater SGR
1900+14, based on ~11.6 Ms of archival data. The 22-150 keV INTEGRAL spectrum
can be well fit by a power law with photon index 1.9 +/- 0.3 and flux F_x =
(1.11 +/- 0.17)E-11 erg/cm^2/s (20-100 keV). A comparison with the 20-100 keV
flux measured in 1997 with BeppoSAX, and possibly associated with SGR 1900+14,
shows a luminosity decrease by a factor of ~5. The slope of the power law above
20 keV is consistent within the uncertainties with that of SGR 1806-20, the
other persistent soft gamma-ray repeater for which a hard X-ray emission
extending up to 150 keV has been reported.Comment: Accepted for publication in Astronomy & Astrophysics. 4 page
Supergiant, fast, but not so transient 4U 1907+09
We have investigated the dipping activity observed in the high-mass X-ray
binary 4U 1907+09 and shown that the source continues to pulsate in the "off"
state, noting that the transition between the "on" and "off" states may be
either dip-like or flare-like. This behavior may be explained in the framework
of the "gated accretion" scenario proposed to explain the flares in supergiant
fast X-ray transients (SFXTs). We conclude that 4U 1907+09 might prove to be a
missing link between the SFXTs and ordinary accreting pulsars.Comment: 4 pages 5 figures, accepted in A&
Population of the Galactic X-ray binaries and eRosita
The population of the Galactic X-ray binaries has been mostly probed with
moderately sensitive hard X-ray surveys so far. The eRosita mission will
provide, for the first time a sensitive all-sky X-ray survey in the 2-10 keV
energy range, where the X-ray binaries emit most of the flux and discover the
still unobserved low-luminosity population of these objects. In this paper, we
briefly review the current constraints for the X-ray luminosity functions of
high- and low-mass X-ray binaries and present our own analysis based the
INTEGRAL 9-year Galactic survey, which yields improved constraints. Based on
these results, we estimate the number of new XRBs to be detected in the eRosita
all-sky surveyComment: accepted for publication in A&
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