1,085 research outputs found
Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
4U 1630-472 is a recurrent X-ray transient classified as a black-hole
candidate from its spectral and timing properties. One of the peculiarities of
this source is the presence of regular outbursts with a recurrence period
between 600 and 730 d that has been observed since the discovery of the source
in 1969. We report on a comparative study on the spectral and timing behaviour
of three consecutive outbursts occurred in 2006, 2008 and 2010. We analysed all
the data collected by the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL) and the Rossi X-ray timing Explorer (RXTE) during these three years
of activity. We show that, in spite of having a similar spectral and timing
behaviour in the energy range between 3 and 30 keV, these three outbursts show
pronounced differences above 30 keV. In fact, the 2010 outburst extends at high
energies without any detectable cut-off until 150-200 keV, while the two
previous outbursts that occurred in 2006 and 2008 are not detected at all above
30 keV. Thus, in spite of a very similar accretion disk evolution, these three
outbursts exhibit totally different characteristics of the Compton electron
corona, showing a softening in their evolution rarely observed before in a low
mass X-ray binary hosting a black hole. We argue the possibility that the
unknown perturbation that causes the outbursts to be equally spaced in time
could be at the origin of this particular behaviour. Finally we describe
several possible scenarios that could explain the regularity of the outbursts,
identifying the most plausible, such as a third body orbiting around the binary
system.Comment: April 2015: accepted for publication in MNRAS. May 2015: in pres
A new model for the X-ray continuum of the magnetized accreting pulsars
Accreting highly magnetized pulsars in binary systems are among the brightest
X-ray emitters in our Galaxy. Although a number of high statistical quality
broad-band (0.1-100 keV) X-ray observations are available, the spectral energy
distribution of these sources is usually investigated by adopting pure
phenomenological models, rather than models linked to the physics of accretion.
In this paper, a detailed spectral study of the X-ray emission recorded from
the high-mass X-ray binary pulsars Cen X-3, 4U 0115+63, and Her X-1 is carried
out by using BeppoSAX and joined Suzaku+NuStar data, together with an advanced
version of the compmag model. The latter provides a physical description of the
high energy emission from accreting pulsars, including the thermal and bulk
Comptonization of cyclotron and bremsstrahlung seed photons along the neutron
star accretion column. The compmag model is based on an iterative method for
solving second-order partial differential equations, whose convergence
algorithm has been improved and consolidated during the preparation of this
paper. Our analysis shows that the broad-band X-ray continuum of all considered
sources can be self-consistently described by the compmag model. The cyclotron
absorption features, not included in the model, can be accounted for by using
Gaussian components. From the fits of the compmag model to the data we inferred
the physical properties of the accretion columns in all sources, finding values
reasonably close to those theoretically expected according to our current
understanding of accretion in highly magnetized neutron stars. The updated
version of the compmag model has been tailored to the physical processes that
are known to occur in the columns of highly magnetized accreting neutron stars
and it can thus provide a better understanding of the high energy radiation
from these sources.Comment: 19 pages, 10 figures, accepted for publication in A&
RX J0440.9+4431: a persistent Be/X-ray binary in outburst
The persistent Be/X-ray binary RX J0440.9+4431 flared in 2010 and 2011 and
has been followed by various X-ray facilities Swift, RXTE, XMM-Newton, and
INTEGRAL. We studied the source timing and spectral properties as a function of
its X-ray luminosity to investigate the transition from normal to flaring
activity and the dynamical properties of the system. We have determined the
orbital period from the long-term Swift/BAT light curve, but our determinations
of the spin period are not precise enough to constrain any orbital solution.
The source spectrum can always be described by a bulk-motion Comptonization
model of black body seed photons attenuated by a moderate photoelectric
absorption. At the highest luminosity, we measured a curvature of the spectrum,
which we attribute to a significant contribution of the radiation pressure in
the accretion process. This allows us to estimate that the transition from a
bulk-motion-dominated flow to a radiatively dominated one happens at a
luminosity of ~2e36 erg/s. The luminosity dependency of the size of the black
body emission region is found to be . This
suggests that either matter accreting onto the neutron star hosted in RX
J0440.9+4431 penetrates through closed magnetic field lines at the border of
the compact object magnetosphere or that the structure of the neutron star
magnetic field is more complicated than a simple dipole close to the surfaceComment: Accepted for publication by A&
XMM-Newton and Swift observations of XTE J1743-363
XTEJ1743-363 is a poorly known hard X-ray transient, that displays short and
intense flares similar to those observed from Supergiant Fast X-ray Transients.
The probable optical counterpart shows spectral properties similar to those of
an M8 III giant, thus suggesting that XTEJ1743-363 belongs to the class of the
Symbiotic X-ray Binaries. In this paper we report on the first dedicated
monitoring campaign of the source in the soft X-ray range with XMM-Newton and
Swift/XRT. T hese observations confirmed the association of XTEJ1743-363 with
the previously suggested M8 III giant and the classification of the source as a
member of the Symbiotic X-ray binaries. In the soft X-ray domain, XTEJ1743-363
displays a high absorption (~6x10^22 cm^-2 ) and variability on time scales of
hundreds to few thousand seconds, typical of wind accreting systems. A
relatively faint flare (peak X-ray flux 3x10^-11 erg/cm^2/s) lasting ~4 ks is
recorded during the XMM-Newton observation and interpreted in terms of the wind
accretion scenario.Comment: Accepted for publication on A&
IGRJ17361-4441: a possible new accreting X-ray binary in NGC6388
IGRJ17361-4441 is a newly discovered INTEGRAL hard X-ray transient, located
in the globular cluster NGC6388. We report here the results of the X-ray and
radio observations performed with Swift, INTEGRAL, RXTE, and the Australia
Telescope Compact Array (ATCA) after the discovery of the source on 2011 August
11. In the X-ray domain, IGRJ17361-4441 showed virtually constant flux and
spectral parameters up to 18 days from the onset of the outburst. The
broad-band (0.5-100 keV) spectrum of the source could be reasonably well
described by using an absorbed power-law component with a high energy cut-off
(N_H\simeq0.8x10^(22) cm^(-2), {\Gamma}\simeq0.7-1.0, and E_cut\simeq25 keV)
and displayed some evidence of a soft component below \sim2 keV. No coherent
timing features were found in the RXTE data. The ATCA observation did not
detect significant radio emission from IGRJ17361-4441, and provided the most
stringent upper limit (rms 14.1 {\mu}Jy at 5.5 GHz) to date on the presence of
any radio source close to the NGC6388 center of gravity. The improved position
of IGRJ17361-4441 in outburst determined from a recent target of opportunity
observation with Chandra, together with the X-ray flux and radio upper limits
measured in the direction of the source, argue against its association with the
putative intermediate-mass black hole residing in the globular cluster and with
the general hypothesis that the INTEGRAL source is a black hole candidate.
IGRJ17361-4441 might be more likely a new X-ray binary hosting an accreting
neutron star. The ATCA radio non-detection also permits us to derive an upper
limit to the mass of the suspected intermediate massive black hole in NGC6388
of <600 M\odot. This is a factor of 2.5 lower than the limit reported
previously.Comment: Accepted for publication on A&A lette
INTEGRAL and Swift observations of IGRJ19294+1816 in outburst
IGRJ19294+1816 was discovered by INTEGRAL in 2009 during a bright X-ray
outburst and was classified as a possible Be X-ray binary or supergiant fast
X-ray transient. On 2010 October 28, the source displayed a second X-ray
outburst and a 2 months-long monitoring with Swift was carried out to follow
the evolution of the source X-ray flux during the event. We report on the
INTEGRAL and Swift observations of the second X-ray outburst observed from
IGRJ19294+1816. We detected pulsations in the X-ray emission from the source at
\sim12.5 s up to 50 keV. The source X-ray flux decreased smoothly during the
two months of observation displaying only marginal spectral changes. Due to the
relatively rapid decay of the source X-ray flux, no significant variations of
the source spin period across the event could be measured. This prevented a
firm confirmation of the previously suggested orbital period of the source at
117 d. This periodicity was also searched by using archival Swift /BAT data. We
detected a marginally significant peak in the periodogram and determined the
best period at 116.2\pm0.6 days (estimated chance probability of a spurious
detection 1%). The smooth decline of the source X-ray flux across the two
months of observations after the onset of the second outburst, together with
its relatively low value of the spin period and the absence of remarkable
changes in the spectral parameters (i.e., the absorption column density),
suggests that IGRJ19294+1816 is most likely another member of the Be X-ray
binaries discovered by INTEGRAL and not a supergiant fast X-ray transient.Comment: Accepted for publication in A&A. 7 pages, 10 figure
PROJECTED LIGHT SYSTEM FOR TRUNK SURFACE RECONSTRUCTION AND VOLUME MEASUREMENT DURING RESPIRATION
There is an increasing interest on developing non invasive and accurate methods to obtain torso shape and deformation during movement. Methods like inductance pletismography (Warren et al. 1989), magnetommetry (Verschakelen & Demedts 1995) and kinematical analysis (Ferrigno et al. 1994) have been proposed to access the pulmonary function based on trunk motion analysis. Measurements of body shape and dimensions are widely used on ergonomic and anthropometry designs fields (Allen et al. 2004) and to estimate body segment parameters for the analysis of human movement (Wicke et al. 2009). The aim of this work was to present a video-based method for trunk volumes measurement during the respiration by means of projected light and surface reconstruction
Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808
We report on the discovery of coherent pulsations at a period of 2.9 ms from
the X-ray transient MAXI J0911-655 in the globular cluster NGC 2808. We
observed X-ray pulsations at a frequency of Hz in three different
observations of the source performed with XMM-Newton and NuSTAR during the
source outburst. This newly discovered accreting millisecond pulsar is part of
an ultra-compact binary system characterised by an orbital period of
minutes and a projected semi-major axis of lt-ms. Based on the mass
function we estimate a minimum companion mass of 0.024 M, which
assumes a neutron star mass of 1.4 M and a maximum inclination angle
of (derived from the lack of eclipses and dips in the light-curve
of the source). We find that the companion star's Roche-Lobe could either be
filled by a hot ( K) pure helium white dwarf with a 0.028
M mass (implying ) or an old (>5 Gyr) brown dwarf
with metallicity abundances between solar/sub-solar and mass ranging in the
interval 0.0650.085 M (16 < < 21). During the outburst the
broad-band energy spectra are well described by a superposition of a weak
black-body component (kT 0.5 keV) and a hard cutoff power-law with photon
index 1.7 and cut-off at a temperature kT 130 keV. Up to
the latest Swift-XRT observation performed on 2016 July 19 the source has been
observed in outburst for almost 150 days, which makes MAXI J0911-655 the second
accreting millisecond X-ray pulsar with outburst duration longer than 100 days.Comment: 7 pages, 5 figures, accepted for publication in A&
Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
4U 1630-472 is a recurrent X-ray transient classified as a black hole candidate from its spectral and timing properties. One of the peculiarities of this source is the presence of regular outbursts with a recurrence period between 600 and 730d that has been observed since the discovery of the source in 1969. We report on a comparative study of the spectral and timing behaviour of three consecutive outbursts that occurred in 2006, 2008 and 2010. We have analysed all the data collected by INTEGRAL and the Rossi X-ray Timing Explorer (RXTE) during these three years of activity. We show that, in spite of having a similar spectral and timing behaviour in the energy range between 3 and 30keV, these three outbursts show pronounced differences above 30keV. In fact, the 2010 outburst extends at high energies without any detectable cut-off until 150-200keV, while the two previous outbursts that occurred in 2006 and 2008 are not detected at all above 30keV. Thus, in spite of a very similar accretion disc evolution, these three outbursts exhibit totally different characteristics of the Compton electron corona, showing a softening in their evolution rarely observed before in a low-mass X-ray binary hosting a black hole. We argue the possibility that the unknown perturbation that causes the outbursts to be equally spaced in time could be at the origin of this particular behaviour. Finally, we describe several possible scenarios that could explain the regularity of the outbursts, identifying the most plausible, such as a third body orbiting around the binary syste
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