Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether a LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5-25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87+/-13 in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g., SWIFT, XMM-Newton, XARM, ATHENA, NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.
In X-ray binary star systems consisting of a compact object that accretes material from an orbiting secondary star, there is no straightforward means to decide if the compact object is a black hole or a neutron star. To assist this classification, we develop a Bayesian statistical model that makes use of the fact that X-ray binary systems appear to cluster based on their compact object type when viewed from a 3-dimensional coordinate system derived from X-ray spectral data. The first coordinate of this data is the ratio of counts in mid to low energy band (color 1), the second coordinate is th…
We report on the archival near-infrared and mid-infrared observations of 7 persistent X-ray sources situated in the Galactic bulge using data from the UKIRT Infrared Deep Sky Survey (UKIDSS), Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and the Wide-field Infrared Survey Explorer (WISE) all-sky survey. We were able to successfully identify, or provide upper flux limits for the systems SAX J1747.0-2853, IGR J17464-2811, AX J1754.2-2754, IGR J17597-2201, IGR J18134-1636, IGR J18256-1035, Ser X-1 and constrain the nature of these systems. In the case of IGR J17597-22…
We describe here the nature, formation and evolution of the supergiant high mass X-ray binary (HMXB) population, i.e. systems accreting the stellar wind of supergiant stars. There are now many new observations, from the high-energy side (mainly from the INTEGRAL satellite), complemented by multi-wavelength observations (mainly in the optical, near and mid-infrared from ESO facilities), showing that a new population of supergiant HMXBs has been recently revealed. We report here on the observational facts about the different categories of HMXBs, allowing to build a consistent scenario explaining…
The accretion/ejection coupling in accreting black hole binaries has been described by empirical relations between the X-ray/radio and X-ray/optical-infrared luminosities. These correlations were initially supposed to be universal. However, recently many sources have been found to produce jets that, given certain accretion-powered luminosities, are fainter than expected from the correlations. This shows that black holes with similar accretion flows can produce a broad range of outflows in power. Here we discuss whether typical parameters of the binary system, as well as the properties of the o…
Very faint X-ray binaries (VFXBs), defined as having peak luminosities Lx of 10^34-10^36 erg/s, have been uncovered in significant numbers, but remain poorly understood. We analyse three published outburst light curves of two transient VFXBs using the exponential and linear decay formalism of King and Ritter (1998). The decay timescales and brink luminosities suggest orbital periods of order 1 hour. We review various estimates of VFXB properties, and compare these with suggested explanations of the nature of VFXBs. We suggest that: 1) VFXB outbursts showing linear decays might be explained as …
In 2018, we reported our discovery of a dozen quiescent X-ray binaries in the central parsec (pc) of the Galaxy (Hailey et al. 2018). In a recent follow-up paper (Mori et al. 2021), we published an extended analysis of these sources and other X-ray binaries (XRBs) in the central pc and beyond, showing that most if not all of the 12 non-thermal sources are likely black hole low-mass X-ray binary (BH-LMXB) candidates. In response, Maccarone et al. 2022 (TM22 hereafter) argued, primarily on the claim that neutron star low-mass X-ray binaries (NS-LMXBs) often do not have short outburst recurrence …
We review the multiwavelength properties of the few known gamma-ray binaries, focusing on extended emission recently resolved with Chandra. We discuss the implications of these findings for the nature of compact objects and for physical processes operating in these systems.
The presence of some X-ray sources in the Galactic Centre region which show variability, but do not show outbursts in over a decade of monitoring has been used to argue for the presence of a large population of stellar mass black holes in this region. A core element of the arguments that these objects are accreting black holes is the claim that neutron stars (NSs) in low mass X-ray binaries (LMXBs) do not have long transient recurrence times. We demonstrate in this paper that about half of the known transient LMXBs with clear signatures for NS primaries have recurrence times in excess of a dec…
Massive stars are predominantly found in binaries and higher order multiples. While the period and eccentricity distributions of OB stars are now well established across different metallicity regimes, the determination of mass-ratios has been mostly limited to double-lined spectroscopic binaries. As a consequence, the mass-ratio distribution remains subject to significant uncertainties. Open questions include the shape and extent of the companion mass-function towards its low-mass end and the nature of undetected companions in single-lined spectroscopic binaries. In this contribution, we prese…
This paper summarises our current understanding of the spectral continuum components observed in black hole X-ray binaries. The consequences for theoretical models are discussed with an emphasis on the constraints set by observations on the nature of the X-ray corona in different spectral states.
Since its launch, the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has discovered hundreds of X-ray sources, many of which lack proper classification. This mission also led to the discovery of new categories of high mass X-ray binaries (HMXB). We use the spectra of the X-Shooter instrument at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) to better understand the nature of 3 accreting binaries (IGR J10101-5654, IGR J11435-6109 and IGR J12489-6243) discovered by INTEGRAL. We mainly focused on the lines and continuum from the X-Shooter spectra. …
I briefly outline the state-paradigm that has emerged from the study of black-hole binaries with RossiXTE. This is the starting point of a number of studies that address the connection between accretion and jet ejection and the physical nature of the hard spectral components in these systems.
Gamma-ray binaries are X-ray binaries with gamma-ray emissions. Their multi-wavelength emissions range from radio, optical, X-ray and to very high energy (TeV). X-ray emissions are crucial to understand the nature of gamma-ray binaries. INTEGRAL and RXTE have covered and monitored most of the gamma-ray binaries in hard and soft X-rays. Here we report the results of several gamma-ray binaries and possible gamma-ray binaries from INTEGRAL and RXTE.
We analyze a flux-limited sample of persistent and bright (with 2-10 keV fluxes exceeding 1.4e-10 erg/s/cm2) low-mass X-ray binaries (LMXBs) in our Galaxy. It is demonstrated that the majority of binary systems with X-ray luminosities below logL(erg/sec)~37.3 have unevolved secondary companions (except for those with white dwarf donors), while systems with higher X-ray luminosity predominantly harbor giant donors. Mass transfer in binary systems with giants significantly shortens their life time thus steepening the X-ray luminosity function of LMXBs at high luminosity. We argue that this is th…
We report on a detailed analysis of the so-called ~1 Hz quasi-periodic oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray binary EXO 0748-676. This type of QPO has previously been shown to have a geometric origin. Our study focuses on the evolution of the QPO as the source moves through the color-color diagram, in which it traces out an atoll-source-like track. The QPO frequency increases from ~0.4 Hz in the hard state to ~25 Hz as the source approaches the soft state. Combining power spectra based on QPO frequency reveals additional features that strongly resemble thos…
We propose an explanation of the Island and Banana states and the relation between Atoll and Z-track sources, constituting a unified model for Low Mass X-ray Binaries (LMXB). We find a dramatic transition at a luminosity of 1 - 2.10^{37} erg/s above which the high energy cut-off E_CO of the Comptonized emission in all sources is low at a few keV. There is thermal equilibrium between the neutron star at ~2 keV and the Comptonizing accretion disk corona (ADC) causing the low E_CO in the Banana state of Atolls and all states of the Z-track sources. Below this luminosity, E_CO increases towards 10…
Black hole X-ray binaries display significant stochastic variability on short time-scales (0.01-100 seconds), with a complex pattern of lags in correlated variability seen in different energy bands. This behaviour is generally interpreted in a model where slow fluctuations stirred up at large radii propagate down through the accretion flow, modulating faster fluctuations generated at smaller radii. Coupling this scenario with radially-stratified emission opens the way to measure the propagation time-scale from data, allowing direct tests of the accretion flow structure. We previously developed…
Gamma-ray binaries are colliding wind binaries (CWB) composed of a massive star a non-accreting pulsar with a highly relativistic wind. Particle acceleration at the shocks results in emission going from extended radio emission to the gamma-ray band. The interaction region is expected to show common features with stellar CWB. Performing numerical simulations with the hydrodynamical code RAMSES, we focus on their structure and stability and find that the Kelvin-Helmholtz instability (KHI) can lead to important mixing between the winds and destroy the large scale spiral structure. To investigate …
We have numerically solved the Grad-Shafranov equation for axisymmetric static MHD equilibria of matter confined at the polar cap of neutron stars. From the equilibrium solutions we explore the stability of the accretion mounds using the PLUTO MHD code. We find that pressure driven modes disrupt the equilibria beyond a threshold mound mass, forming dynamic structures, as matter spreads over the neutron star surface. Our results show that local variation of magnetic field will significantly affect the shape and nature of the cyclotron features observed in the spectra of High Mass X-ray Binaries…
In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. I then report on the discovery of two new populations of HMXBs hosting supergiant stars, recently revealed by a wealth of new observations, coming from the high energy side (INTEGRAL, Swift, XMM, Chandra satellites), and complemented by multi-wavelength optical/infrared observations (mainly ESO facilities). The first population is constituted of obscured supergiant HMXBs, the seco…
Discovery of the 6.7-hour periodicity in the X-ray source 1E 161348-5055 in RCW 103 has led to investigations of the nature of this periodicity. We explore a model for 1E 161348-5055, wherein a fast-spinning neutron star with a magnetic field $\sim 10^{12}$ G in a young pre-Low-Mass X-ray Binary (pre-LMXB) with an eccentric orbit of period 6.7 hr operates in the "propeller" phase. The 6.7-hr light curve of 1E 161348-5055 can be quantitatively accounted by a model of orbitally-modulated mass transfer through a viscous accretion disk and subsequent propeller emission (both Illarionov-Sunyaev typ…
In this study, we examine the properties of donor stars of the three recently discovered ultraluminous X-ray sources (ULXs) powered by rotating neutron stars. For this purpose, we constructed a theoretical relation between the X-ray luminosity ($L_{\rm{X}}$) and the orbital period ($P_{\rm{orb}}$) suitable for ULXs with neutron stars. By using this new $L_{\rm{X}} - P_{\rm{orb}}$ relation, we attempt to determine the currently unknown nature of donor stars in ULXs associated with neutron stars. Especially, comparing the observed properties with the stellar evolution tracks, we suggest that the…
The accretion/ejection coupling in accreting black hole binaries has been described by empirical relations between the X-ray/radio and X-ray/optical-infrared luminosities. These correlations were initially thought to be universal. However, recently many sources have been found to produce jets that, given certain accretion-powered luminosities, are fainter than expected from the earlier correlations. This shows that black holes with similar accretion flows can produce a broad range of outflows in power, suggesting that some other parameters might be tuning the accretion/ejection coupling. Recen…
The aim of this review is to describe the nature, formation and evolution of the three kinds of high mass X-ray binary (HMXB) population: i. systems hosting Be stars (BeHMXBs), ii. systems accreting the stellar wind of supergiant stars (sgHMXBs), and iii. supergiant stars overflowing their Roche lobe. There are now many new observations, from the high-energy side (mainly from the INTEGRAL satellite), complemented by multi-wavelength observations (mainly in the optical, near and mid-infrared from ESO facilities), showing that a new population of supergiant HMXBs has been recently revealed. New …
The dynamics of coalescing compact binaries can be affected by the environment in which the systems evolve, leaving detectable signatures into the emitted gravitational signal. In this paper we investigate the ability of gravitational-wave detectors to constrain the nature of the environment in which compact binaries merge. We parametrize a variety of environmental effects by modifying the phase of the gravitational signal emitted by black hole and neutron star binaries. We infer the bounds on such effects by current and future generation of interferometers, studying their dependence on the bi…
Gamma-ray binaries allow us to study physical processes such as particle acceleration up to very-high energies and gamma-ray emission and absorption with changing geometrical configurations on a periodic basis. These sources produce outflows of radio-emitting particles whose structure can be imaged with Very Long Baseline Interferometry (VLBI). We have studied the changing morphology of the gamma-ray binaries LS I +61 303 and LS 5039, and we have discovered the extended emission of PSR B1259-63 and HESS J0632+057. Based on these results, we have established the basic properties and behaviour o…
We summarize the results of our long-running campaign to help understand the nature of high-mass X-ray binaries (HMXBs), emphasizing recent Suzaku observations of IGR J16207-5129 and IGR J17391-3021. Thanks to the expanding ranks of HMXBs in our Galaxy, we are able to perform more reliable statistical analyses on the three currently-known sub-classes of HMXB: those with supergiant companions (SGXBs); those with Be companions (BEXBs); and the enigmatic Supergiant Fast X-ray Transients (SFXTs). We discuss new diagnostic tools, akin to the "Corbet diagram," in which HMXBs tend to segregate based …
The INTEGRAL satellite has revealed a major population of supergiant High Mass X-ray Binaries in our Galaxy, revolutionizing our understanding of binary systems and their evolution. This population, constituted of a compact object orbiting around a massive and luminous supergiant star, exhibits unusual properties, either being extremely absorbed, or showing very short and intense flares. An intensive set of multi-wavelength observations has led us to reveal their nature, and to show that these systems are wind-fed accretors, closely related to massive star-forming regions. In this paper I desc…
Accreting stellar-mass black holes appear to populate two branches in a radio:X-ray luminosity plane. We have investigated the X-ray variability properties of a large number of black hole low-mass X-ray binaries, with the aim of unveiling the physical reasons underlying the radio-loud/radio-quiet nature of these sources, in the context of the known accretion-ejection connection. A reconsideration of the available radio and X-ray data from a sample of black hole X-ray binaries confirms that being radio-quiet is the more normal mode of behaviour for black hole binaries. In the light of this we c…
Ultra-compact binaries (UCBs) are systems containing compact or degenerate stars with orbital periods less than one hour. Tens of millions of UCBs are predicted to exist within theGalaxy emitting gravitational waves (GWs) at mHz frequencies. Combining GW searches with electromagnetic (EM) surveys like Gaia and LSST will yield a comprehensive, multimessenger catalog of UCBs in the galaxy. Joint EM and GW observations enable measurements of masses, radii, and orbital dynamics far beyond what can be achieved by independent EM or GW studies. GW+EM surveys of UCBs in the galaxy will yield a trove o…
We present near-infrared (NIR) imaging observations of three transient neutron star X-ray binaries, SAX J1753.5-2349, SAX J1806.5-2215 and AX J1754.2-2754. All three sources are members of the class of `very faint' X-ray transients which exhibit X-ray luminosities $L_X\lesssim10^{36}$ erg s$^{-1}$. The nature of this class of sources is still poorly understood. We detect NIR counterparts for all three systems and perform multi-band photometry for both SAX J1753.5-2349 and SAX J1806.5-2215, including narrow-band Br$_γ$ photometry for SAX J1806.5-2215. We find that SAX J1753.5-2349 is significan…
In recent years, thanks to the continuous surveys performed by INTEGRAL and Swift satellites, our knowledge of the hard X-ray/soft gamma-ray sky has greatly improved. As a result it is now populated with about 2000 sources, both Galactic and extra-galactic, mainly discovered by IBIS and BAT instruments. Many different follow-up campaigns have been successfully performed by using a multi-wavelength approach, shedding light on the nature of a number of these new hard X-ray sources. However, a fraction are still of a unidentified nature. This is mainly due to the lack of lower energy observations…
The Large Magellanic Cloud (LMC) currently hosts around 23 high mass X-ray binaries (HMXBs) of which most are Be/X-ray binaries. The LMC XMM-Newton survey provided follow-up observations of previously known X-ray sources that were likely HMXBs, as well as identifying new HMXB candidates. In total 19 candidate HMXBs were selected based on their X-ray hardness ratios. In this paper we present red and blue optical spectroscopy, obtained with SALT and the SAAO 1.9-m telescope, plus a timing analysis of the long term optical light curves from OGLE to confirm the nature of these candidates. We find …
The INTEGRAL satellite has revealed a major population of supergiant High Mass X-ray Binaries in our Galaxy, revolutionizing our understanding of binary systems and their evolution. This population, constituted of a compact object orbiting around a massive and luminous supergiant star, exhibits unusual properties, either being extremely absorbed, or showing very short and intense flares. An intensive set of multi-wavelength observations has led us to reveal their nature, and to show that these systems are wind-fed accretors, closely related to massive star-forming regions. In this paper I desc…
We present preliminary results on Herschel/PACS mid/far-infrared photometric observations of INTEGRAL supergiant High Mass X-ray Binaries (HMXBs), with the aim of detecting the presence and characterizing the nature of absorbing material (dust and/or cold gas), either enshrouding the whole binary systems, or surrounding the sources within their close environment. These unique observations allow us to better characterize the nature of these HMXBs, to constrain the link with their environment (impact and feedback), and finally to get a better understanding of the formation and evolution of such …
In this proof-of-concept study we demonstrate that in a binary system mass can be transferred toward an accreting compact object at extremely high rate. If the transferred mass is efficiently converted to X-ray luminosity (with disregard of the classical Eddington limit) or if the X-rays are focused into a narrow beam then binaries can form extreme ULX sources with the X-ray luminosity of Lx>10^42 erg/s. For example, Lasota & King argued that the brightest known ULX (HLX-1) is a regular binary system with a rather low-mass compact object (a stellar-origin black hole or a neutron star). The pre…
The X-ray emission from accreting black-holes and neutron stars features strong variability on sub-second time scales, with very complex and broad phenomenology. From high-frequency quasi-periodic oscillations to rapidly changing X-ray burst oscillations to millisecond pulsations, these are weak signals immersed in strong noise and their study is pushing instrument capabilities to their limit. The scientific significance of fast time variability studies are both astronomical (properties of accretion flows, nature and evolution of sources) and physical (effects of General Relativity, equation o…
The discovery of a binary comprising a black hole (BH) and a millisecond pulsar (MSP) would yield insights into stellar evolution and facilitate exquisitely sensitive tests of general relativity. Globular clusters (GCs) are known to harbor large MSP populations and recent studies suggest that GCs may also retain a substantial population of stellar mass BHs. We modeled the formation of BH+MSP binaries in GCs through exchange interactions between binary and single stars. We found that in dense, massive clusters most of the dynamically formed BH+MSP binaries will have orbital periods of 2 to 10 d…
The high mass X-ray binaries (HMXBs) provide an exciting framework to investigate the evolution of massive stars and the processes behind binary evolution. HMXBs have shown to be good tracers of recent star formation in galaxies and might be important feedback sources at early stages of the Universe. Furthermore, HMXBs are likely the progenitors of gravitational wave sources (BH--BH or BH--NS binaries that may merge producing gravitational waves). In this work, we investigate the nature and properties of HMXB population in star-forming galaxies. We combine the results from the population synth…
During its first 2 years of mission the Fermi-LAT instrument discovered more than 1,800 gamma-ray sources in the 100 MeV to 100 GeV range. Despite the application of advanced techniques to identify and associate the Fermi-LAT sources with counterparts at other wavelengths, about 40% of the LAT sources have no a clear identification remaining "unassociated". The purpose of my Ph.D. work has been to pursue a statistical approach to identify the nature of each Fermi-LAT unassociated source. To this aim, we implemented advanced machine learning techniques, such as logistic regression and artificia…
We report on an analysis of RXTE data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities the source switched between two types of Z source behavior and at low luminosities we observed a transition from Z source to atoll source behavior. These transitions between subclasses primarily manifest themselves as changes in the shapes of the tracks in X-ray color-color and hardness-intensity diagrams, but they are accomp…
Very faint X-ray binaries appear to be transient in many cases with peak luminosities much fainter than that of usual soft X-ray transients, but their nature still remains elusive. We investigate the possibility that this transient behaviour is due to the same thermal/viscous instability which is responsible for outbursts of bright soft X-ray transients, occurring in ultracompact binaries for adequately low mass-transfer rates. More generally, we investigate the observational consequences of this instability when it occurs in ultracompact binaries. We use our code for modelling the thermal-vis…
The physics behind the dramatic and unpredictable X-ray variability of Active Galactic Nuclei (AGN) has eluded astronomers since it was discovered. We present an analysis of Swift XRT observations of 44 AGN with at least 20 Swift observations. We define HR-slope as the change of Hardness Ratio (HR) with luminosity ($L$). This slope is measured for all objects in order to: 1. Classify different AGN according to their HR-HR-slope relation and 2. compare HR-$L/L_\mathrm{Edd}$ trends with those observed in X-ray binaries for the 27 AGN with well measured black hole masses. We compare results using…
We propose a novel method to test the binary black hole (BBH) nature of compact binaries detectable by gravitational wave (GW) interferometers and hence constrain the parameter space of other exotic compact objects. The spirit of the test lies in the "no-hair" conjecture for black holes where all properties of a black hole are characterised by the mass and the spin of the black hole. The method relies on observationally measuring the quadrupole moments of the compact binary constituents induced due to their spins. If the compact object is a Kerr black hole (BH), its quadrupole moment is expres…
According to the "no-hair" conjecture, a Kerr black hole (BH) is completely described by its mass and spin. In particular, the spin-induced quadrupole moment of a Kerr BH with mass $m$ and dimensionless spin $χ$ can be written as $Q=-κ\,m^3χ^2$, where $κ_{\rm BH}=1$. Thus by measuring the spin-induced quadrupole parameter $κ$, we can test the binary black hole nature of compact binaries and distinguish them from binaries comprised of other exotic compact objects, as proposed in [N. V. Krishnendu et al., PRL 119, 091101 (2017)]. Here, we present a Bayesian framework to carry out this test where…
In the observation of gravitational waves (GWs) from a compact binary coalescence system where the mass of one of the companions is $\leq 5~M_{\odot}$ the nature of the object is ambiguous until the measurements of tidal effects give evidence for the presence of a neutron star (NS) or a low mass black hole (BH). The relevance of tidal effects in a neutron star--black hole (NSBH) binary system depends crucially upon the mass and the spin of the companion BH. These effects become important predominantly when the binary system is of comparable mass and/or has large aligned spins. Depending upon t…
The LISA (Laser Interferometer Space Antenna) mission will observe in the low frequency band from 0.1 mHz to 1 Hz. In this regime, we expect the galactic binaries to be the dominant (by number) sources of gravitational waves signal. Considering that galactic binaries are composed of the most magnetized astrophysical objects in the universe (i.e., the white dwarfs and the neutron stars), LISA is expected to bring new informations about the origin and the nature of magnetism inside degenerated stars. Currently, the data processing assumes that the galactic binary systems are non-magnetic and in …
In this review I discuss the characteristics and the formation of all classes of millisecond pulsars (MSPs). The main focus is on the stellar astrophysics of X-ray binaries leading to the production of fully recycled MSPs with white dwarf (WD) or substellar semi-degenerate companions. Depending on the nature of the companion star MSPs are believed to form from either low-mass X-ray binaries (LMXBs) or intermediate-mass X-ray binaries (IMXBs). For each of these two classes of X-ray binaries the evolutionary status of the donor star -- or equivalently, the orbital period -- at the onset of the R…
Close-orbit binaries consisting of two compact objects are a center of attention because of the detection of gravitational-radiation-induced mergers. The creation of close, compact-object binaries involves physical processes that are not yet well understood; there are open questions about the manner in which two compact objects come to be close enough to merge within a Hubble time. Here we explore an important, and likely common physical process: mass transfer from a third star in a wider, hierarchical orbit. Mass added to the close binary's components can reduce the time to merger and can eve…
Since it started observing the sky, the INTEGRAL satellite has revealed new categories of High Mass X-ray binaries in our Galaxy. These observations raise important questions on the formation and evolution of such rare and short-living objects. We present here new observations that enable us to reveal or constrain the nature of 15 new INTEGRAL sources. After previous photometric and spectroscopic campaigns of observations in optical and near infrared, new spectroscopy and photometry were performed at ESO in optical/NIR with EMMI and SOFI on the NTT in 2008 and 2010 on a sample of INTEGRAL sour…
