2,488 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&
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&
BeppoSAX observations of XTE J1946+274
We report on the BeppoSAX monitoring of a giant outburst of the transient
X-ray pulsar XTE J1946+274 in 1998. The source was detected with a flux of ~ 4
x 10^(-9) erg cm^(-2) s^(-1) (in 0.1 - 120 keV range). The broadband spectrum,
typical for accreting pulsars, is well described by a cutoff power law with a
cyclotron resonance scattering feature (CRSF) at ~ 38 keV. This value is
consistent with earlier reports based on the observations with Suzaku at factor
of ten lower luminosity, which implies that the feature is formed close to the
neutron star surface rather than in the accretion column. Pulsations with P ~
15.82 s were observed up to ~ 70 keV. The pulse profile strongly depends on
energy and is characterised by a "soft" and a "hard" peaks shifted by half
period, which suggests a strong phase dependence of the spectrum, and that two
components with roughly orthogonal beam patterns are responsible for the
observed pulse shape. This conclusion is supported by the fact that the CRSF,
despite its relatively high energy, is only detected in the spectrum of the
soft peak of the pulse profile. Along with the absence of correlation of the
line energy with luminosity, this could be explained in the framework of the
recently proposed "reflection" model for CRSF formation. However more detailed
modelling of both line and continuum formation are required to confirm this
interpretation
Zeroes of combinations of Bessel functions and mean charge of graphene nanodots
We establish some properties of the zeroes of sums and differences of
contiguous Bessel functions of the first kind. As a byproduct, we also prove
that the zeroes of the derivatives of Bessel functions of the first kind of
different orders are interlaced the same way as the zeroes of Bessel functions
themselves. As a physical motivation, we consider gated graphene nanodots
subject to Berry-Mondragon boundary conditions. We determine the allowed energy
levels and calculate the mean charge at zero temperature. We discuss in detail
its dependence on the gate (chemical) potential.Comment: vesrion accepted to Theoretical and Mathematical Physics, 18 pages, 1
figur
Charge density and conductivity of disordered Berry-Mondragon graphene nanoribbons
We consider gated graphene nanoribbons subject to Berry-Mondragon boundary
conditions in the presence of weak impurities. Using field--theoretical
methods, we calculate the density of charge carriers (and, thus, the quantum
capacitance) as well as the optical and DC conductivities at zero temperature.
We discuss in detail their dependence on the gate (chemical) potential, and
reveal a non-linear behaviour induced by the quantization of the transversal
momentum.Comment: 17 pages, version accepted for publication in EPJ
A non-pulsating neutron star in the supernova remnant HESS J1731-347 / G353.6-0.7 with a carbon atmosphere
Context: The CCO candidate in the center of the supernova remnant shell HESS
J1731-347 / G353.6-0.7 shows no pulsations and exhibits a blackbody-like X-ray
spectrum. If the absence of pulsations is interpreted as evidence for the
emitting surface area being the entire neutron star surface, the assumption of
the measured flux being due to a blackbody emission translates into a source
distance that is inconsistent with current estimates of the remnant's distance.
Aims: With the best available observational data, we extended the pulse period
search down to a sub-millisecond time scale and used a carbon atmosphere model
to describe the X-ray spectrum of the CCO and to estimate geometrical
parameters of the neutron star. Methods: To search for pulsations we used data
of an observation of the source with XMM-Newton performed in timing mode. For
the spectral analysis, we used earlier XMM-Newton observations performed in
imaging mode, which permits a more accurate treatment of the background. The
carbon atmosphere models used to fit the CCO spectrum are computed assuming
hydrostatic and radiative equilibria and take into account pressure ionization
and the presence of spectral lines. Results: Our timing analysis did not reveal
any pulsations with a pulsed fraction above ~8% down to 0.2 ms. This finding
further supports the hypothesis that the emitting surface area is the entire
neutron star surface. The carbon atmosphere model provides a good fit to the
CCO spectrum and leads to a normalization consistent with the available
distance estimates of the remnant. The derived constraints on the mass and
radius of the source are consistent with reasonable values of the neutron star
mass and radius. After the CCO in Cas A, the CCO in HESS J1731-347 / G353.6-0.7
is the second object of this class for which a carbon atmosphere model provides
a consistent description of X-ray emission.Comment: 6 pages, 5 figures, accepted for publication in
Astronomy&Astrophysic
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