138 research outputs found
The IBIS soft gamma-ray sky after 1000 INTEGRAL orbits
We report here an all-sky soft gamma-ray source catalog based on IBIS
observations performed during the first 1000 orbits of INTEGRAL. The database
for the construction of the source list consists of all good quality data
available from launch in 2002 up to the end of 2010. This corresponds to
110 Ms of scientific public observations with a concentrated coverage on
the Galactic Plane and extragalactic deep exposures. This new catalog includes
939 sources above a 4.5 sigma significance threshold detected in the 17-100 keV
energy band, of which 120 represent previously undiscovered soft gamma-ray
emitters. The source positions are determined, mean fluxes are provided in two
main energy bands, and are reported together with the overall source exposure.
Indicative levels of variability are provided, and outburst times and durations
are given for transient sources. Comparison is made with previous IBIS
catalogs, and those from other similar missions.Comment: 65 pages, 9 figures, 2 tables, accepted for publication in ApJ
Supplement
The XMM Newton and INTEGRAL observations of the supergiant fast X-ray transient IGR J16328-4726
The accretion mechanism producing the short flares observed from the
Supergiant Fast X-ray Transients (SFXT) is still highly debated and forms a
major part in our attempts to place these X-ray binaries in the wider context
of the High Mass X-ray Binaries.
We report on a 216 ks INTEGRAL observation of the SFXT IGR J16328-4726
(August 24-27, 2014) simultaneous with two fixed-time observations with XMM
Newton (33ks and 20ks) performed around the putative periastron passage, in
order to investigate the accretion regime and the wind properties during this
orbital phase. During these observations, the source has shown luminosity
variations, from 4x10^{34} erg/s to 10^{36} erg/s, linked to spectral
properties changes. The soft X-ray continuum is well modeled by a power law
with a photon index varying from 1.2 up to 1.7 and with high values of the
column density in the range 2-4x10^{23}/cm^2. We report on the presence of iron
lines at 6.8-7.1 keV suggesting that the X-ray flux is produced by accretion of
matter from the companion wind characterized by density and temperature
inhomogeneities
Swift/XRT monitoring of the Supergiant Fast X-ray Transient IGR J18483-0311 for an entire orbital period
IGR J18483-0311 is an X-ray pulsar with transient X-ray activity, belonging
to the new class of High Mass X-ray Binaries called Supergiant Fast X-ray
Transients. This system is one of the two members of this class, together with
IGR J11215-5952, where both the orbital (18.52d) and spin period (21s) are
known. We report on the first complete monitoring of the X-ray activity along
an entire orbital period of a Supergiant Fast X-ray Transient. These Swift
observations, lasting 28d, cover more than one entire orbital phase
consecutively. They are a unique data-set, which allows us to constrain the
different mechanisms proposed to explain the nature of this new class of X-ray
transients. We applied the new clumpy wind model for blue supergiants developed
by Ducci et al. (2009), to the observed X-ray light curve. Assuming an
eccentricity of e=0.4, the X-ray emission from this source can be explained in
terms of the accretion from a spherically symmetric clumpy wind, composed of
clumps with different masses, ranging from 10^{18}g to 5x 10^{21}g.Comment: Accepted for publication in MNRAS. 7 pages, 7 figures, 2 table
XMM-Newton observations of IGRJ18410-0535: The ingestion of a clump by a supergiant fast X-ray transient
IGRJ18410-0535 is a supergiant fast X-ray transients. This subclass of
supergiant X-ray binaries typically undergoes few- hour-long outbursts reaching
luminosities of 10^(36)-10^(37) erg/s, the occurrence of which has been
ascribed to the combined effect of the intense magnetic field and rotation of
the compact object hosted in them and/or the presence of dense structures
("clumps") in the wind of their supergiant companion. IGR J18410-0535 was
observed for 45 ks by XMM-Newton as part of a program designed to study the
quiescent emission of supergiant fast X-ray transients and clarify the origin
of their peculiar X-ray variability. We carried out an in-depth spectral and
timing analysis of these XMM-Newton data. IGR J18410-0535 underwent a bright
X-ray flare that started about 5 ks after the beginning of the observation and
lasted for \sim15 ks. Thanks to the capabilities of the instruments on-board
XMM-Newton, the whole event could be followed in great detail. The results of
our analysis provide strong convincing evidence that the flare was produced by
the accretion of matter from a massive clump onto the compact object hosted in
this system. By assuming that the clump is spherical and moves at the same
velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl
\simeq1.4\times10^(22) g and Rcl \simeq8\times10^(11) cm. These are in
qualitative agreement with values expected from theoretical calculations. We
found no evidence of pulsations at \sim4.7 s after investigating coherent
modulations in the range 3.5 ms-100 s. A reanalysis of the archival ASCA and
Swift data of IGR J18410-0535, for which these pulsations were previously
detected, revealed that they were likely to be due to a statistical fluctuation
and an instrumental effect, respectively.Comment: Accepted for publication on A&A. V2: Inserted correct version of
Fig.1
Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. I. The nature of the companion star
Context: The INTEGRAL hard X-ray observatory has revealed an emerging
population of highly obscured X-ray binary systems through multi-wavelength
observations. Previous studies have shown that many of these sources are
high-mass X-ray binaries hosting neutron stars orbiting around luminous and
evolved companion stars. Aims: To better understand this newly-discovered
population, we have selected a sample of sources for which an accurate
localisation is available to identify the stellar counterpart and reveal the
nature of the companion star and of the binary system. Methods: We performed an
intensive study of a sample of thirteen INTEGRAL sources, through
multi-wavelength optical to NIR photometric and spectroscopic observations,
using EMMI and SofI instruments at the ESO NTT telescope. We performed accurate
astrometry and identified candidate counterparts for which we give the optical
and NIR magnitudes. We detected many spectral lines allowing us to determine
the spectral type of the companion star. We fitted with stellar black bodies
the mid-infrared to optical spectral energy distributions of these sources.
From the spectral analysis and SED fitting we identified the nature of the
companion stars and of the binary systems. (abridged).Comment: A&A in press; The official date of acceptance is 15/12/2007; 25
pages, 6 figures, 8 tables. New version with language editing required by
edito
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
Chandra localisation and optical/NIR follow-up of Galactic X-ray sources
We investigate a sample of eleven Galactic X-ray sources recently discovered
with INTEGRAL or RXTE with the goal of identifying their optical and/or
near-infrared (NIR) counterpart. For this purpose new Chandra positions of nine
objects are presented together with follow-up observations of all the targets
in the optical and NIR. For the four sources IGR J16194-2810, IGRJ 16479-4514,
IGR J16500-3307 and IGR J19308+530, the Chandra position confirms an existing
association with an optical/NIR object, while for two sources (XTE J1716-389
and 18490-0000) it rules out previously proposed counterparts indicating new
ones. In the case of IGR J17597-220, a counterpart is selected out of the
several possibilities proposed in the literature and we present the first
association with an optical/NIR source for J16293-4603 and XTE J1743-363.
Moreover, optical/NIR observations are reported for XTE J1710-281 and IGR
J17254-3257: we investigate the counterpart to the X-ray sources based on their
XMM-Newton positions. We discuss the nature of each system considering its
optical/NIR and X-ray properties.Comment: 15 pages,14 figures. Accepted for publication on MNRA
Hard X-ray flares in IGR J08408-4503 unveil clumpy stellar winds
Context : A 1000-s flare from a new hard X-ray transient, IGR J08408-4503,
was observed by INTEGRAL on May 15, 2006 during the real-time routine
monitoring of IBIS/ISGRI images performed at the INTEGRAL Science Data Centre.
The flare, detected during a single one-hour long pointing, peaked at 250 mCrab
in the 20-40 keV energy range.
Aims : Multi-wavelength observations, combining high-energy and optical data,
were used to unveil the nature of IGR J08408-4503.
Methods : A search in all INTEGRAL public data for other bursts from IGR
J08408-4503 was performed, and the detailed analysis of another major flare is
presented. The results of two Swift Target of Opportunity observations are also
described. Finally, a study of the likely optical counterpart, HD 74194, is
provided.
Results : IGR J08408-4503 is very likely a supergiant fast X-ray transient
(SFXT) system. The system parameters indicate that the X-ray flares are
probably related to the accretion of wind clumps on a compact object orbiting
about 1E13 cm from the supergiant HD 74194. The clump mass loss rate is of the
order of 1E-6 solar mass/yr.
Conclusions : Hard X-ray flares from SFXTs allow to probe the stellar winds
of massive stars, and could possibly be associated with wind perturbations due
to line-driven instabilities.Comment: 5 pages with 5 figures. Published as a Letter in Astronomy &
Astrophysic
New fast X-ray transient IGR J18462-0223 discovered by the INTEGRAL observatory
Details of the discovery of a new X-ray source, IGR J18462-0223, on October
12, 2007, during a short (several hours), intense (~ 35 mCrab at the peak)
outburst of hard radiation by the IBIS/ISGRI gamma-ray telescope onboard the
INTEGRAL observatory are given. The detection of another earlier outburst from
this source occurred on April 28, 2006, in the archival data of the telescope
is reported. We present the results of the source's localization and our
spectral/timing analysis of the observational data. The source may turn out to
be yet another representative of the continuously growing population of fast
X-ray transients, which are the focus of attention because of the
identification of their optical counterparts with early-type supergiants
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
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