3,101 research outputs found
Unveiling the hard X-ray spectrum from the "burst-only" source SAX J1753.5-2349 in outburst
Discovered in 1996 by BeppoSAX during a single type-I burst event, SAX
J1753.5-2349 was classified as "burst-only" source. Its persistent emission,
either in outburst or in quiescence, had never been observed before October
2008, when SAX J1753.5-2349 was observed for the first time in outburst. Based
on INTEGRAL observations,we present here the first high-energy emission study
(above 10 keV) of a so-called "burst-only". During the outburst the SAX
J1753.5-2349 flux decreased from 10 to 4 mCrab in 18-40 keV, while it was found
being in a constant low/hard spectral state. The broad-band (0.3-100 keV)
averaged spectrum obtained by combining INTEGRAL/IBIS and Swift/XRT data has
been fitted with a thermal Comptonisation model and an electron temperature >24
keV inferred. However, the observed high column density does not allow the
detection of the emission from the neutron star surface. Based on the whole set
of observations of SAX J1753.5-2349, we are able to provide a rough estimate of
the duty cycle of the system and the time-averaged mass-accretion rate. We
conclude that the low to very low luminosity of SAX J1753.5-2349 during
outburst may make it a good candidate to harbor a very compact binary system.Comment: 5 pages, 3 figures, 2 tables; accepted for publication in MNRAS
Letter
Unveiling the nature of IGR J17177-3656 with X-ray, NIR and Radio observations
We report on the first broad-band (1-200 keV) simultaneous Chandra-INTEGRAL
observations of the recently discovered hard X-ray transient IGR J17177-3656
that took place on 2011, March 22, about two weeks after the source discovery.
The source had an average absorbed 1-200 keV flux of about 8x10^(-10) erg
cm^(-2) s^(-1). We extracted a precise X-ray position of IGR J17177-3656, RA=17
17 42.62, DEC= -36 56 04.5 (90% uncertainty of 0.6"). We also report Swift,
near infrared and quasi simultaneous radio follow-up observations. With the
multi-wavelength information at hand, we propose IGR J17177-3656 is a low-mass
X-ray binary, seen at high inclination, probably hosting a black hole.Comment: 8 pages, 8 figures, accepted for publication in Ap
Searching for supergiant fast X-ray transients with Swift
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs)
hosting a neutron star and an OB supergiant companion. We examine the available
Swift data, as well as other new or archival/serendipitous data, on three
sources: IGR J17407-2808, 2XMM J185114.3-000004, and IGR J18175-2419, whose
X-ray characteristics qualify them as candidate SFXT, in order to explore their
properties and test whether they are consistent with an SFXT nature. As IGR
J17407-2808 and 2XMM J185114.3-000004 triggered the Burst Alert Telescope on
board Swift, the Swift data allow us to provide their first arcsecond
localisations, leading to an unequivocal identification of the source CXOU
J174042.0-280724 as the soft X-ray counterpart of IGR J17407-2808, as well as
their first broadband spectra, which can be fit with models generally
describing accreting neutron stars in HMXBs. While still lacking optical
spectroscopy to assess the spectral type of the companion, we propose 2XMM
J185114.3-000004 as a very strong SFXT candidate. The nature of IGR J17407-2808
remains, instead, more uncertain. Its broad band properties cannot exclude that
the emission originates from either a HMXB (and in that case, a SFXT) or, more
likely, a low mass X-ray binary. Finally, based on the deep non-detection in
our XRT monitoring campaign and a careful reanalysis of the original Integral
data in which the discovery of the source was first reported, we show that IGR
J18175-2419 is likely a spurious detection.Comment: Accepted for publication in Astronomy and Astrophysics. 12 pages, 11
figures, 6 table
INTEGRAL/RossiXTE high-energy observation of a state transition of GX 339-4
On 2004 August 15, we observed a fast (shorter than 10 hours) state
transition in the bright black-hole transient GX 339-4 simultaneously with
RossiXTE and INTEGRAL. This transition was evident both in timing and spectral
properties. Combining the data from PCA, HEXTE and IBIS, we obtained good
quality broad-band (3-200 keV) energy spectra before and after the transition.
These spectra indicate that the hard component steepened. Also, the high-energy
cutoff that was present at ~70 keV before the transition was not detected after
the transition. This is the first time that an accurate determination of the
broad-band spectrum across such a transition has been measured on a short time
scale. It shows that, although some spectral parameters do not change abruptly
through the transition, the high-energy cutoff increases/disappears rather
fast. These results constitute a benchmark on which to test theoretical models
for the production of the hard component in these systems.Comment: Accepted for publication in MNRAS (9 pages, 6 figures
Broad-band X-ray spectral evolution of GX 339-4 during a state transition
We report on X-ray and soft gamma-ray observations of the black-hole
candidate GX 339-4 during its 2007 outburst, performed with the RXTE and
INTEGRAL satellites. The hardness-intensity diagram of all RXTE/PCA data
combined shows a q-shaped track similar to that observed in previous
outbursts.The evolution in the diagram suggested that a transition from
hard-intermediate state to soft-intermediate state occurred, simultaneously
with INTEGRAL observations performed in March. The transition is confirmed by
the timing analysis presented in this work, which reveals that a weak type-A
quasi-periodic oscillation (QPO) replaces a strong type-C QPO. At the same
time, spectral analysis shows that the flux of the high-energy component shows
a significant decrease in its flux. However, we observe a delay (roughly one
day) between variations of the spectral parameters of the high-energy component
and changes in the flux and timing properties. The changes in the high-energy
component can be explained either in terms the high-energy cut-off or in terms
of a variations in the reflection component. We compare our results with those
from a similar transition during the 2004 outburst of GX 339-4.Comment: 8 pages, 6 figures, accepted for publication in MNRAS Main Journa
Signature of the presence of a third body orbiting around XB 1916-053
The ultra-compact dipping source \object{XB 1916-053} has an orbital period
of close to 50 min and a companion star with a very low mass (less than 0.1
M). The orbital period derivative of the source was estimated to be
s/s through analysing the delays associated with the
dip arrival times obtained from observations spanning 25 years, from 1978 to
2002. The known orbital period derivative is extremely large and can be
explained by invoking an extreme, non-conservative mass transfer rate that is
not easily justifiable. We extended the analysed data from 1978 to 2014, by
spanning 37 years, to verify whether a larger sample of data can be fitted with
a quadratic term or a different scenario has to be considered. We obtained 27
delays associated with the dip arrival times from data covering 37 years and
used different models to fit the time delays with respect to a constant period
model.We find that the quadratic form alone does not fit the data. The data are
well fitted using a sinusoidal term plus a quadratic function or,
alternatively, with a series of sinusoidal terms that can be associated with a
modulation of the dip arrival times due to the presence of a third body that
has an elliptical orbit. We infer that for a conservative mass transfer
scenario the modulation of the delays can be explained by invoking the presence
of a third body with mass between 0.10-0.14 M, orbital period around
the X-ray binary system of close to 51 yr and an eccentricity of . In a non-conservative mass transfer scenario we estimate that the
fraction of matter yielded by the degenerate companion star and accreted onto
the neutron star is , the neutron star mass is
M, and the companion star mass is 0.028 M. (Abridged)Comment: 13 pages, 9 figures. Accepted for publication in A&
Activity from SAX J1747.0-2853 and KS 1741-293 detected by INTEGRAL Galactic Bulge Monitoring
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