985 research outputs found
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
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&
Modern Integrated Associations: Comparative Analysis of Economic Growth Factors
In the article, the results of the research, which purpose is to ground and assess the factors of economic growth of regional integration communities and national economies of member countries that develop them, are presented. The foreign trade, mutual trade turnover, and domestic demand are allocated as such factors. The authors has applied the novelty in their methodology which in contrast to the traditional assessment method of growth factors of integration communities and their participants, is based on comparison of two components — external and domestic demand, based on dividing the external demand on two components: the first one is pure export (the difference between export and import is a component of cumulative demand) of goods in integration community, i.e. the pure export of mutual trade; the second one is a pure export of foreign trade of goods outside of the integration association. Scope of the research is seven most known regional integrated units arose at different times and being at different stages of development — the European Union, North American Free Trade Area, Association of Southeast Asian Nations, Southern American Common Market, Asia-Pacific Economic Cooperation, and also member countries of the Eurasian integration — the Customs Union and Common Free Market Zone developed into the Eurasian Economic Union in January 1, 2015. In conclusion, it is noted that the integration develops successfully only in the conditions of the rise in national economies of the participating countries. Crisis economies have to deal more with internal problems than to resolve integration issues.The article has been prepared within the project «Eurasian integration: asymmetries and efficiency» with financial support of the grant № 1275/GF4 of the Ministry of Education and Science of the Republic of Kazakhstan»
Optical and near-infrared photometric monitoring of the transient X-ray binary A0538-66 with REM
The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical
variability. Despite numerous studies, the intrinsic properties underlying its
anomalous behaviour remain poorly understood. Since 2014 September we are
conducting the first quasi-simultaneous optical and near-infrared photometric
monitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM)
telescope, aiming to understand the properties of this binary system. We found
that the REM lightcurves show fast flares lasting one or two days that repeat
almost regularly every ~16.6 days, the orbital period of the neutron star. If
the optical flares are powered by X-ray outbursts through photon reprocessing,
the REM lightcurves indicate that A0538-66 is still active in X-rays: bright
X-ray flares (L_x > 1E37 erg/s) could be observable during the periastron
passages. The REM lightcurves show a long-term variability that is especially
pronounced in the g band and decreases with increasing wavelength, until it no
longer appears in the near-infrared lightcurves. In addition, A0538-66 is
fainter with respect to previous optical observations most likely due to the
higher absorption of the stellar radiation of a denser circumstellar disc. On
the basis of the current models, we interpret these observational results with
a circumstellar disc around the Be star observed nearly edge-on during a
partial depletion phase. The REM lightcurves also show short-term variability
on timescales of ~1 day possibly indicative of perturbations in the density
distribution of the circumstellar disc caused by the tidal interaction with the
neutron star.Comment: Accepted for publication in Astronomy & Astrophysic
Stable accretion from a cold disc in highly magnetized neutron stars
The aim of this paper is to investigate the transition of a strongly
magnetized neutron star into the accretion regime with very low accretion rate.
For this purpose we monitored the Be-transient X-ray pulsar GRO J1008-57
throughout a full orbital cycle. The current observational campaign was
performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV)
between two subsequent Type I outbursts in January and September 2016. The
expected transition to the propeller regime was not observed. However, the
transitions between different regimes of accretion were detected. In
particular, after an outburst the source entered a stable accretion state
characterised by the accretion rate of ~10^14-10^15 g/s. We associate this
state with accretion from a cold (low-ionised) disc of temperature below ~6500
K. We argue that a transition to such accretion regime should be observed in
all X-ray pulsars with certain combination of the rotation frequency and
magnetic field strength. The proposed model of accretion from a cold disc is
able to explain several puzzling observational properties of X-ray pulsars.Comment: 8 pages, 3 figures, 1 table, accepted by A&
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