We report results from the analysis of XMM-Newton and INTEGRAL data of IGR J16479-4514. The unpublished XMM-Newton observation, performed in 2012, occurred during the source eclipse. No point-like X-ray emission was detected from the source, conversely extended X-ray emission was clearly detected up to a size distance compatible with a dust scattering halo produced by the source X-ray emission before being eclipsed by its companion donor star. The diffuse emission of the dust-scattering halo could be observed without any contamination from the central point X-ray source, compared to a previous XMM-Newton observation published in 2008. Our comprehensive analysis of the 2012 unpublished spectrum of the diffuse emission as well as of the 2008 re-analysed spectra extracted from three adjacent time intervals and different extraction regions (optimized for point-like and extended emission) allowed us to clearly disentangle the scattering halo spectrum from the residual point-like emission during the 2008 eclipse. Moreover, the point-like emission detected in 2008 could be separated into two components attributed to the direct emission from the source and to scattering in the stellar wind, respectively. From archival unpublished INTEGRAL data, we identified a very strong (3$\times$10$^{-8}$ erg cm$^{-2}$ s$^{-1}$) and fast (25 minutes duration) flare which was classified as giant hard X-ray flare since the measured peak-luminosity is 7$\times$10$^{37}$ erg s$^{-1}$. Giant X-ray flares from SFXTs are very rare, to date only one has been reported from a different source. We propose a physical scenario to explain the origin in the case of IGR J16479-4514.
We report here on the XMM-Newton observations of the three supergiant fast X-ray transients (SFXT) XTE J1739-302, IGRJ08408-4503, and IGRJ18410-0535. For the latter source we only discuss some preliminary results of our data analysis. Some interpretation is provided for the timing and spectral behavior of the three sources in terms of the different theoretical models proposed so far to interpret the behavior of the SFXTs.
The supergiant fast X-ray transient (SFXT) system IGR J17544-2619 has displayed many large outbursts in the past and is considered an archetypal example of SFXTs. A search of the INTEGRAL/ISGRI data archive from MJD 52698-54354 has revealed 11 outbursts and timing analysis of the light curve identifies a period of 4.926$\pm$0.001 days which we interpret as the orbital period of the system. We find that large outbursts occasionally occur outside of periastron and place an upper limit for the radius of the supergiant of <23R$_{\sun}$.
Phase-targeted RXTE observations have allowed us to detect a transient 71.49 \pm 0.02 s signal that is most likely to be originating from the supergiant fast X-ray transient IGR J17544-2619. The phase-folded light curve shows a possible double-peaked structure with a pulsed flux of ~4.8*10^-12 erg cm^-2 s^-1 (3-10 keV). Assuming the signal to indicate the spin period of the neutron star in the system, the provisional location of IGR J17544-2619 on the Corbet diagram places the system within the classical wind-fed supergiant XRB region. Such a result illustrates the growing trend of supergiant …
Timing analysis of the INTEGRAL-IBIS and Swift-BAT light curves of the Supergiant Fast X-ray Transient (SFXT) IGR J16465-4507 has identified a period of 30.32+/-0.02 days which we interpret as the orbital period of the binary system. In addition 11 outbursts (9 of which are previously unpublished) have been found between MJD 52652 to MJD 54764, all of which occur close to the region of the orbit we regard as periastron. From the reported flux outbursts, we found a dynamical range in the interval ~30-80. Although in this regard IGR J16465-4507 cannot be considered a classical SFXT for which typ…
We present the results of the XMM-Newton observations of five hard X-ray emitters: IGR J08262-3736, IGR J17354-3255, IGR J16328-4726, SAX J1818.6-1703, and IGR J17348-2045. The first source is a confirmed supergiant high mass X-ray binary, the following two are candidates supergiant fast X-ray transients, SAX J1818.6-1703 is a confirmed supergiant fast X-ray transient and IGR J17348-2045 is one of the still unidentified objects discovered with INTEGRAL. The XMM-Newton observations permitted the first detailed soft X-ray spectral and timing study of IGR J08262-3736 and provided further support …
IGR J17503-2636 is a hard X-ray transient discovered by INTEGRAL on 2018 August 11. This was the first ever reported X-ray emission from this source. Following the discovery, follow-up observations were carried out with Swift, Chandra, NICER, and NuSTAR. We report in this paper the analysis and results obtained from all these X-ray data. Based on the fast variability in the X-ray domain, the spectral energy distribution in the 0.5-80 keV energy range, and the reported association with a highly reddened OB supergiant at ~10 kpc, we conclude that IGR J17503-2636 is most likely a relatively faint…
We report on new X-ray outbursts observed with Swift from three Supergiant Fast X-ray Transients (SFXTs): XTEJ1739-302, IGRJ17544-2619 and IGRJ08408-4503. The former two outbursts were caught during the monitoring campaign we have been performing with the Swift satellite since October 2007: XTEJ1739-302 underwent a new outburst on 2008, August 13, IGRJ17544-2619 on 2008, September 4, while IGRJ08408-4503 on 2008, September 21. While XTEJ1739-302 and IGRJ08408-4503 bright emission triggered the Swift/Burst Alert Telescope, IGRJ17544-2619 did not, thus we could perform a spectral investigation o…
Context. Supergiant fast X-ray transients are a subclass of high mass X-ray binaries that host a neutron star accreting mass from the wind of its OB supergiant companion. They are characterized by an extremely pronounced and rapid variability in X-rays, which still lacks an unambiguous interpretation. A number of deep pointed observations with XMM-Newton have been carried out to study the quiescent emission of these sources and gain insight into the mechanism that causes their X-ray variability. Aims. We continued this study by using three XMM-Newton observations of the two supergiant fast X-r…
We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming that the compact object in IGR J17544-2619 is indeed a neutron star. This is the first measurement of the magnetic field in a SFXT. The inferred magnetic field strength, B = (1.45 +/- 0.03) * 10^12 G * (1+z) is typical of neutron stars in X-ray binaries, and rules out a magnetar nature for the compact object. We…
We report on the Swift monitoring of the candidate supergiant fast X-ray transient (SFXT) IGR J16418-4532, for which both orbital and spin periods are known (~3.7d and ~1250s, respectively). Our observations, for a total of ~43ks, span over three orbital periods and represent the most intense and complete sampling of the light curve of this source with a sensitive X-ray instrument. With this unique set of observations we can address the nature of this transient. By applying the clumpy wind model for blue supergiants to the observed X-ray light curve, and assuming a circular orbit, the X-ray em…
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…
Supergiant fast X-ray transients (SFXTs) are X-ray binary systems with a supergiant companion and likely a neutron star, which show a fast ($\sim 10^3$ s) and high variability with a dynamic range up to $10^{5-6}$. Given their extreme properties, they are considered among the most valuable laboratories to test accretion models. Recently, the orbital parameters of a member of this class, IGR J08408-4503, were obtained from optical observations. We used this information, together with X-ray observations from previous publications and new results from X-ray and optical data collected by INTEGRAL …
We analysed the IGR J16465-4507 Burst Alert Teelescope survey data collected during the first 54 months of the Swift mission. The source is in a crowded field and it is revealed through an ad hoc imaging analysis at a significance level of ~14 standard deviations. The 15-50 keV average flux is ~3E-11 erg/cm^2/s. The timing analysis reveals an orbital period of 30.243 +/- 0.035 days. The folded light curve shows the presence of a wide phase interval of minimum intensity, lasting ~20% of the orbital period. This could be explained with a full eclipse of the compact object in an extremely eccentr…
We present the orbital X-ray modulation study of three high mass X- ray binary systems, IGR J18027-2016, IGR J18483-0311 and IGR J16318-4848 using data obtained with RXTE-ASM, Swift-BAT and INTEGRAL-ISGRI. Using the long term light curves of the eclipsing HMXB IGR J18027-2016, obtained with Swift-BAT in the energy range 15-50 keV and INTEGRAL-ISGRI in the energy range 22-40 keV, we have determined three new mid eclipse times. The newly determined mid eclipse times together with the known values were used to derive an accurate value of the orbital period of 4.5693(4) d at MJD 52168 and an upper…
We report here discovery of a 3.32 day orbital period in the Supergiant Fast X-ray Transient (SFXT) source IGR J16479-4514. Using the long term light curve of this source obtained with Swift-BAT in the energy range of 15-50 keV, we have clearly detected an orbital modulation including a full eclipse of duration ~0.6 day. In the hard X-ray band of the BAT instrument, the eclipse ingress and egress are rapid. We have also used the long term light curve obtained with the RXTE -ASM in the energy range of 1.5-12 keV. Taken independently, the detection of orbital modulation in the RXTE -ASM light cu…
We report on the first focused hard X-ray view of the absorbed supergiant system IGRJ18027-2016 performed with the NuSTAR observatory. The pulsations are clearly detected with a period of $P_{spin}=139.866(1)$ s and a pulse fraction of about 50-60% at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time scale of more than dozen years with an average spin-down rate of $dP/dt\simeq6\times10^{-10}$ s/s. This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at ener…
Supergiant X-ray binaries usually comprise a neutron star accreting from the wind of a OB supergiant companion. They are classified as classical systems and the supergiant fast X-ray transients (SFXTs). The different behavior of these sub-classes of sources in X-rays, with SFXTs displaying much more pronounced variability, is usually (at least) partly ascribed to different physical properties of the massive star clumpy stellar wind. In case of SFXTs, a systematic investigation of the effects of clumps on flares/outbursts of these sources has been reported by Bozzo et al. (2017) exploiting the …
IGR J18483-0311 is a supergiant fast X-ray transient whose compact object is located in a wide (18.5 d) and eccentric (e~0.4) orbit, which shows sporadic outbursts that reach X-ray luminosities of ~1e36 erg/s. We investigated the timing properties of IGR J18483-0311 and studied the spectra during bright outbursts by fitting physical models based on thermal and bulk Comptonization processes for accreting compact objects. We analysed archival INTEGRAL data collected in the period 2003-2010, focusing on the observations with IGR J18483-0311 in outburst. We searched for pulsations in the INTEGRAL …
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 orig…
We report on combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient IGR J16418-4532. The observations targeted the X-ray eclipse region of IGR J16418-4532s orbit with continuous INTEGRAL observations across ~25% of orbital phase and two quasi-simultaneous XMM-Newton observations of length 20ks and 14ks, occurring during and just after the eclipse respectively. An enhanced INTEGRAL emission history is provided with 19 previously unreported outbursts identified in the archival 18-60 keV data set. The XMM-Newton eclipse observation showed prominent Fe-emission and a …
Wind-fed supergiant X-ray binaries are precious laboratories not only to study accretion under extreme gravity and magnetic field conditions, but also to probe still highly debated properties of massive star winds. These includes the so-called clumps, originated from the inherent instability of line driven winds, and larger structures. In this paper, we report on the results of the last (and not yet published) monitoring campaigns that our group has been carrying out since 2007 with both XMM-Newton and the Swift Neil Gehrels observatory. Data collected with the EPIC cameras on-board XMM-Newton…
Among the different types of sources shining in the high energy sky, gamma-ray binaries are rapidly becoming the subject of major interest. In fact, in the last few years a number of High Mass X-ray Binaries (HMXBs) have been firmly detected from MeV to TeV energies, providing secure evidences that particles can be efficiently accelerated up to very high energies in such galactic systems. Similarly to this general and emerging class of gamma-ray binaries, in principle Supergiant Fast X-ray Transients (SFXTs) have all the "ingredients" to be transient high energy emitters. In this context, the …
XMM-Newton observations of the supergiant fast X-ray transient IGR$~$J17544$-$2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provides a refined estimate of the orbital period at 4.9272$\pm$0.0004 days. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM-Newton observations (each lasting $\sim$15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR$~$J17544$-$2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the ord…
A significant fraction of high-mass X-ray binaries are supergiant fast X-ray transients (SFXTs). The prime model for the physics governing their X-ray behaviour suggests that the winds of donor OB supergiants are magnetized. To investigate if magnetic fields are indeed present in the optical counterparts of such systems, we acquired low-resolution spectropolarimetric observations of the two optically brightest SFXTs, IGR J08408-4503 and IGR J11215-5952 with the ESO FORS2 instrument during two different observing runs. No field detection at a significance level of 3sigma was achieved for IGR J0…
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries associated with OB supergiant companions and characterised by an X-ray flaring behaviour whose dynamical range reaches 5 orders of magnitude on timescales of a few hundred to thousands of seconds. Current investigations concentrate on finding possible mechanisms to inhibit accretion in SFXTs and explain their unusually low average X-ray luminosity. We present the Swift observations of an exceptionally bright outburst displayed by the SFXT IGR J17544-2619 on 2014 October 10 when the source achieved a peak luminosity of $3\tim…
We report on the Swift/X-ray Telescope (XRT) monitoring of the field of view around the candidate supergiant fast X-ray transient (SFXT) IGR J17354-3255, which is positionally associated with the AGILE/GRID gamma-ray transient AGL J1734-3310. Our observations, which cover 11 days for a total on-source exposure of about 24 ks, span 1.2 orbital periods (P_orb=8.4474 d) and are the first sensitive monitoring of this source in the soft X-rays. These new data allow us to exploit the timing variability properties of the sources in the field to unambiguously identify the soft X-ray counterpart of IGR…
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as a supergiant fast X-ray transient. It was observed in outburst many times, but its quiescent state is still poorly known. Here we present the results of XMM-Newton, Swift, and Chandra observations of IGRJ18483-0311. These data improved the X-ray position of the source, and provided new information on the timing and spectral properties of IGR J18483-0311 in quiescence. We report the detection of pulsations in the quiescent X-ray emission of this source, and give for the first time a measurement of the spin-period deriv…
We present the results of combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient (SFXT) IGR J17354$-$3255. Three XMM-Newton observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first an initial pointing to identify the correct source in the field of view and the latter two performed around periastron. Simultaneous INTEGRAL observations across $\sim66\%$ of the orbital cycle were analysed but the source was neither detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a range of moderately bright X-ray activity but there are …
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, t…
We report on a broad-band X-ray study (0.5-250 keV) of the Supergiant Fast X-ray Transient IGR J18483-0311 using archival INTEGRAL data and a new targeted XMM-Newton observation. Our INTEGRAL investigation discovered for the first time an unusually long X-ray activity (3-60 keV) which continuously lasted for at least 11 days, i.e. a significant fraction (about 60%) of the entire orbital period, and spanned orbital phases corresponding to both periastron and apastron passages. This prolongated X-ray activity is at odds with the much shorter durations marking outbursts from classical SFXTs espec…
We report on FORS2 spectroscopy aiming at the identification of four Galactic Plane sources discovered by $INTEGRAL$, IGR J18088-2741, IGR J18381-0924, IGR J17164-3803, and IGR J19173+0747, complemented by $XMM$-$Newton$ spectroscopy for IGR J18381-0924. The presence of broad emission lines of neutral H and He and a flat Balmer decrement Hα/Hβ show that IGR J18088-2741 is a cataclysmic variable located beyond 8 kpc. For IGR J18381-0924, the detection of red-shifted Hα and neutral O emission signatures and the absence of narrow forbidden emission lines point towards a low-luminosity Seyfert 1.9…
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…
We present the results of Chandra and XMM-Newton observations for six hard X-ray sources (IGR J12134-6015, IGR J18293-1213, IGR J18219-1347, IGR J17350-2045, IGR J18048-1455, XTE J1901+014) from the INTEGRAL all-sky survey. Based on these observations, we have improved significantly the localization accuracy of the objects and, therefore, have managed to identify their optical counterparts. Using data from the publicly available 2MASS and UKIDSS infrared sky surveys as well as data from the SOFI/NTT telescope (European Southern Observatory), we have determined the magnitudes of the optical cou…
IGR J11215-5952 is a hard X-ray transient discovered in 2005 April by INTEGRAL and a member of the new class of HMXB, the Supergiant Fast X-ray Transients (SFXTs). While INTEGRAL and RXTE observations have shown that the outbursts occur with a periodicity of ~330 days, Swift data have recently demonstrated that the true outburst period is ~165 days. IGR J11215-5952 is the first discovered SFXT displaying periodic outbursts, which are possibly related to the orbital period. We performed a Guest Investigator observation with Swift that lasted 20ks and several follow-up Target of Opportunity (ToO…
IGRJ17361-4441 is a hard transient recently observed by the INTEGRAL satellite. The source, close to the center of gravity of the globular cluster NGC 6388, quickly became the target of follow-up observations conducted by the Chandra, Swift/XRT and RXTE observatories. Here, we concentrate in particular on a set of observations conducted by the XMM-Newton satellite during two slews, in order to get the spectral information of the source and search for spectral variations. The spectral parameters determined by the recent XMM-Newton slew observations were compared to the previously known results.…
We report on the Swift observations of the candidate supergiant fast X-ray transient (SFXT) IGR J16418-4532, which has an orbital period of ~3.7 d. Our monitoring, for a total of ~43 ks, spans over three orbits and represents the most intense and complete sampling along the orbital period of the light curve of this source. If one assumes a circular orbit, the X-ray emission from this source can be explained by accretion from a spherically symmetric clumpy wind from a blue supergiant, composed of clumps with different masses, ranging from ~5x10^16 g to 10^21g.
We studied the soft-X-ray emission of five hard-X sources: IGR J08262-3736, IGR J17354-3255, IGR J16328-4726, SAX J1818.6-1703 and IGR J17348-2045. These sources are: a confirmed supergiant high mass X-ray binary (IGR J08262-3736); candidates (IGR J17354-3255, IGR J16328- 4726) and confirmed (SAX J1818.6-1703) supergiant fast X-ray transients; IGR J17348-2045 is one of the as-yet unidentified objects discovered with INTEGRAL. Thanks to dedicated XMM-Newton observations, we obtained the first detailed soft X-ray spectral and timing study of IGR J08262-3736. The results obtained from the observa…
About 30% of the sources in the 4th INTEGRAL-IBIS catalogue are unidentified in that they lack an optical counterpart. To be able to classify them, X-ray observations are of crucial importance as they can place tighter constraints on the high energy error box, which is usually of the order of a few arcminutes, and allow their broad band spectrum to be studied. To this aim we have cross-correlated the list of all unidentified IBIS sources in the fourth catalogue with the archive of all XMM-Newton pointings, finding a set of 6 objects with archival data. For 1 of them, IGR J17331-2406, no X-ray …
We report on a broad-band X-ray study (0.5-60 keV) of the poorly known candidate Supergiant Fast X-ray Transient (SFXT) IGR J18462-0223, and on optical and near-infrared (NIR) followup observations of field objects. The out-of-outburst X-ray state has been investigated for the first time with archival INTEGRAL/IBIS, ASCA, Chandra and Swift/XRT observations. This allowed us to place stringent 3 sigma upper limits on the soft (0.5-10 keV) and hard (18-60 keV) X-ray emission of 2.9x10^-13 erg cm^-2 s^-1 and 8x10^-12 erg cm^-2 s^-1, respectively; the source was also detected during an intermediate…
Many new and unidentified Galactic sources have recently been revealed by ongoing hard X-ray surveys. A significant fraction of these have been shown to be the type of accreting white dwarfs known as cataclysmic variables (CVs). Follow-up observations are often required to categorize and classify these sources, and may also identify potentially unique or interesting cases. One such case is IGR J18007-4146, which is likely a CV based on follow-up Chandra observations and constraints from optical/IR catalogs. Utilizing simultaneous XMM-Newton and NuSTAR observations, as well as the available opt…
IGR J04571+4527 and Swift J0525.6+2416 are two hard X-ray sources detected in the Swift/BAT and INTEGRAL/IBIS surveys. They were proposed to be magnetic cataclysmic variables of the Intermediate Polar (IP) type, based on optical spectroscopy. IGR J04571+4527 also showed a 1218 s optical periodicity, suggestive of the rotational period of a white dwarf, further pointing towards an IP classification. We here present detailed X-ray (0.3-10 keV) timing and spectral analysis performed with XMM-Newton, complemented with hard X-ray coverage (15-70 keV) from Swift/BAT. These are the first high signal …
High Mass X-ray Binaries (HMXB) have been revealed by a wealth of multi-wavelength observations, from X-ray to optical and infrared domain. After describing the 3 different kinds of HMXB, we focus on 3 HMXB hosting supergiant stars: IGR J16320-4751, IGR J16465-4507 and IGR J16318-4848, respectively called "The Good", "The Bad" and "The Ugly". We review in these proceedings what the observations of these sources have brought to light concerning our knowledge of HMXB, and what part still remains in the dark side. Many questions are still pending, related to accretion processes, stellar wind prop…
The unidentified source IGR J16328-4726 was covered with INTEGRAL observations for a long period (~9.8Ms) and was undetectable for most of the time while showing a very recurrent micro-activity with a duration from tens minutes to several hours. We report the discovery of two strong outbursts started at 53420.65 MJD and 54859.99 MJD respectively, the first with a duration of ~1 hour and the second with a lower limit on the duration of ~3.5 hours. Furthermore, the source have been detected in nine other short pointings with significance between 4 and 5 sigma as well as in a one of the revolutio…
We present the first direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 10000 in luminosity and gives a detailed look at SFXT behavior.
We present spectral and energy dependent timing characteristics of the hard X-ray transient IGR J17497-2821 based on XMM-Newton observations performed five and nine days after its outburst on 2006 September 17. We find that the source spectra can be well described by a hard (Gamma ~ 1.50) powerlaw and a weak multicolour disk blackbody with inner disk temperature kT_{in} ~ 0.2 KeV. A broad iron K - alpha line with FWHM ~ 27000 Km/s, consistent with that arising from an accretion disk truncated at large radius, was also detected. The power density spectra of IGR J17497 - 2821, derived from the h…
A growing group of low-mass X-ray binaries are found to be accreting at very-faint X-ray luminosities of <1E36 erg/s (2-10 keV). Once such system is the new X-ray transient IGR J17494-3030. We present Swift and XMM-Newton observations obtained during its 2012 discovery outburst. The Swift observations trace the peak of the outburst, which reached a luminosity of ~7 E35 (D/8 kpc)^2 erg/s (2-10 keV). The XMM-Newton data were obtained when the outburst had decayed to an intensity of ~ 8 E34 (D/8 kpc)^2 erg/s. The spectrum can be described by a power-law with an index of ~1.7 and requires an addit…
Suzaku observations are presented for the high-mass X-ray binaries IGR J16207-5129 and IGR J17391-3021 (=XTE J1739-302). For IGR J16207-5129, we provide the first X-ray broadband (0.5--60 keV) spectrum from which we confirm a large intrinsic column density (nH = 1.6e23 /cm2), and we constrain the cutoff energy for the first time (Ec = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles > …
Since its launch, the X-ray and gamma-ray observatory INTEGRAL satellite has revealed a new class of high-mass X-ray binaries (HMXB) displaying fast flares and hosting supergiant companion stars. Optical and infrared (OIR) observations in a multi-wavelength context are essential to understand the nature and evolution of these newly discovered celestial objects. The goal of this multiwavelength study (from ultraviolet to infrared) is to characterise the properties of IGR J16465-4507, to confirm its HMXB nature and that it hosts a supergiant star. We analysed all OIR, photometric and spectroscop…
We report the discovery using data from the Swift Burst Alert Telescope (BAT) of superorbital modulation in the wind-accretion supergiant high-mass X-ray binaries 4U 1909+07 (= X 1908+075), IGR J16418-4532, and IGR J16479-4514. Together with already known superorbital periodicities in 2S 0114+650 and IGR J16493-4348, the systems exhibit a monotonic relationship between superorbital and orbital periods. These systems include both supergiant fast X-ray transients (SFXTs) and classical supergiant systems, and have a range of inclination angles. This suggests an underlying physical mechanism which…
Classical Supergiant X-ray Binaries (SGXBs) and Supergiant Fast X-ray Transients (SFXTs) are two types of High-mass X-ray Binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. However, such…
IGR J17091-3624 is a low mass X-ray binary (LMXB) which received wide attention from the community thanks to its similarities with the bright black hole system GRS 1915+105. Both systems exhibit a wide range of highly structured X-ray variability during outburst, with time scales from few seconds to tens of minutes, which make them unique in the study of mass accretion in LMXBs. In this work we present a general overview into the long-term evolution of IGR J17091-3624, using Swift/XRT observations from the onset of the 2011-2013 outburst in February 2011 to the end of the last bright outburst …
IGR J16320-4751 is a highly obscured HMXB source containing a very slow neutron star ($P_{spin}\sim1300$ sec) orbiting its supergiant companion star with a period of $\sim$9 days. It shows high column density ($N_{H}\sim2-5\times10^{23}$ $cm^{-2}$) in the spectrum, and a large variation in flux along the orbit despite not being an eclipsing source. We report on some peculiar timing and spectral features from archival XMM-Newton observation of this source including 8 observations taken during a single orbit. The pulsar shows large timing variability in terms of average count rate from different…
Results are presented for XMM-Newton observations of five hard X-ray sources discovered by INTEGRAL in the direction of the Scutum Arm. Each source received more than 20 ks of effective exposure time. We provide refined X-ray positions for all five targets enabling us to pinpoint the most likely counterpart in optical/infrared archives. Spectral and timing information (much of which are provided for the first time) allow us to give a firm classification for IGR J18462-0223 and to offer tentative classifications for the others. For IGR J18462-0223, we discovered a coherent pulsation period of 9…
We report here on the most recent results obtained on a new class of High Mass X-ray Binaries, the Supergiant Fast X-ray Transients. Since October 2007, we have been performing a monitoring campaign with Swift of four SFXTs (IGRJ17544-2916, XTEJ1739-302, IGRJ16479-4514 and the X-ray pulsar AXJ1841.0-0536) for about 1-2 ks, 2-3 times per week, allowing us to derive the previously unknown long term properties of this new class of sources (their duty cycles, spectral properties in outbursts and out-of-outbursts, temporal behaviour). We also report here on additional Swift observations of two SFXT…
We report the results from an archival XMM-Newton observation of the Supergiant Fast X-ray Transient (SFXT) IGR J18483-0311 during its apastron passage. The measured 0.5--10 keV luminosity state (1.3$\times10^{33}$ erg s$^{-1}$) is the lowest ever reported in the literature, it is best fitted by an absorbed black body model yielding parameters consistent with previous measurements. In addition, we find evidence of an emission line feature at $\sim$3.3 keV in the 0.5--10 keV EPIC-pn source spectrum. We show that its physical explanation in terms of atomic emission line appears unlikely and conv…
The supergiant fast X-ray transient source IGR J16479-4514 was observed in outburst two times with Swift. Its quiescent state was investigated in-depth only once in 2008 through a relatively long pointed observation with XMM-Newton. The latter observation was taken about 1.7 days after the outburst in 2008, and showed an X-ray eclipse-like event, likely caused by the supergiant companion. At present, this is the only supergiant fast X-ray transient that displayed an evidence for an X-ray eclipse. Here we carry out a comparison between the most recent outburst of IGRJ16479-4514, caught by Swift…
IGR J16479-4514 is a member of the Supergiant Fast X-ray transient (SFXT) class. We present the light curves of its latest outburst, which occurred on January 29, 2009. During this outburst, IGR J16479-4514 showed prolonged activity lasting several days. The presence of eclipses was successfully tested.
We report on the discovery of mHz quasi-periodic oscillations (QPOs) from the high mass X-ray binary (HMXB) IGRJ19140+0951, during a 40 ks XMM-Newton observation performed in 201 5, which caught the source in its faintest state ever observed. At the start of the observation, IGRJ19140+0951 was at a low flux of 2$\times$10$^{-12}$~erg~cm$^{-2}$~s$^{-1}$ ( 2-10 keV; L$_{\rm X}$=3$\times$10$^{33}$~erg~s$^{-1}$ at 3.6 kpc), then its emission rised reaching a flux 10 times higher, in a flare-like activity. The investigation of the pow er spectrum reveals the presence of QPOs, detected only in the s…
