C. Cabanac

Studying the X-ray hysteresis in GX 339−4: the disc and iron line over one decade

We report on a comprehensive and consistent investigation into the X-ray emission from GX 339−4. All public observations in the 11 year RXTE archive were analysed. Three different types of model ‐ single power law, broken power law and a disc + power law ‐ were fitted to investigate the evolution of the disc, along with a fixed Gaussian component at 6.4 keV to investigate any iron line in the spectrum. We show that the relative variation in flux and X-ray colour between the two best sampled outbursts are very similar. The decay of the disc temperature during the outburst is clearly seen in the soft state. The expected decay is SDisc ∝ T 4 ; we measure T 4.75±0.23 . This implies that the inner disc radius is approximately constant in the soft state. We also show a significant anticorrelation between the iron line equivalent width (EW) and the X-ray flux in the soft state while in the hard state the EW is independent of the flux. This results in hysteresis in the relation between X-ray flux and both line flux and EW. To compare the X-ray binary outburst to the behaviour seen in active galactic nuclei (AGN), we construct a disc fraction luminosity diagram for GX 339−4, the first for an X-ray binary. The shape qualitatively matches that produced for AGN. Linking this with the radio emission from GX 339−4 the change in radio spectrum between the disc and power-law-dominated states is clearly visible.

INTEGRAL and XMM-Newton observations of the X-ray pulsar IGR J16320-4751/AX J1631.9-4752

We report on observations of the X-ray pulsar IGR J16320−4751 (a.k.a. AX J1631.9−4752) performed simultaneously with INTEGRAL and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼ 1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with bein g constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare p eriod. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, a nd show that the pulse is solely due to variations of the X-ray flux emitted by the source and no t to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energised cloud in which the compact object is embedded.

Unveiling the nature of the high energy source IGR J19140+0951

We report on high energy observations of IGR J19140+0951 performed with RXTE on three occasions in 2002, 2003 and 2004, and INTEGRAL during a very well sampled and unprecedented high energy coverage of this source from early-March to mid-May 2003. Our analysis shows that IGR J19140+0951 spends most of its time in a very low luminosity state, probably corresponding to the state observed with RXTE, and characterised by thermal Comptonisation. In some occasions we observe variations of the luminosity by a factor of about 10 during which the spectrum can show evidence for a thermal component, besides thermal Comptonisation by a hotter plasma than during the low luminosity state. The spectral parameters obtained from the spectral fits to the INTEGRAL and RXTE data strongly suggest that IGR J19140+0951 hosts a neutron star rather than a black hole. Very importantly, we observe variations of the absorption column density (with a value as high as ∼10 23 cm −2 ). Our spectral analysis also reveals a bright iron line detected with both RXTE/PCA and INTEGRAL/JEM-X, at different levels of luminosity. We discuss these results and the behaviour of IGR J19140+0951, and show, by comparison with other well known systems (Vela X-1, GX 301−2, 4U 2206+54), that IGR J19140+0951 is most probably a High Mass X-ray Binary.

Discovery of a new INTEGRAL source: IGR J19140+0951

IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the INTEGRAL satellite in March 2003. We report the details of the discovery, using an improved position for the analysis. We have performed a si- multaneous study of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two different states. From the results of our analysis we propose that IGR J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron star although a black hole cannot be completely ruled out.

Unveiling the Nature of the New Transient IGR J19140+0951

IGR J19140+0951 was discovered during the first observation campaign of the famous microquasar GRS1915+105 (PI Hannikainen) by INTEGRAL IBIS/ISGRI instrument. The source, which is 1° from GRS1915+105 (corrected position), shows high variations of its X-ray luminosity and spectral variations on timescales from seconds to hours. According to the early INTEGRAL (AO1) and further RXTE (AO8 and AO9) observations and regarding the spectral behavior and the timescale variability, we propose the source to be a galactic X-ray binary probably hosting a neutron star.

A Global Study of X-ray Binaries

We present preliminary results on a global study of X-ray binaries using 14 Ms of data from the Rossi X-ray Timing Explorer satellite. Our initial study on GX 339-4 is recapped as an introduction to the methods used. We use a consistent analysis scheme for all objects, with three different spectral models to fit the powerlaw and disc components. We also take into account the possibility of a line being present in the data. The resulting almost 4000 observations allow the tracking of the spectral properties of the binaries as they evolve through an outburst. Our investigations concentrate on the disc and line properties of the binaries when in outburst. We also show the Disc-Fraction Luminosity diagram for the population of X-ray binaries studied which will enable us to further links with AGN.

The Accretion‐Ejection Mechanisms in X‐ray Binaries: an Unified View

We present a new keplerian accretion disc solution, the so‐called Jet Emitting Disc (JED hereafter), which is part of global self‐consistent disc‐jet MHD structure. In our framework, a large scale, organized vertical magnetic field is threading the JED giving birth, when conditions are met, to stationnary self‐collimated non relativistic jets. The main condition is that the magnetic pressure Pmag must be of the order of the total pressure Ptot in the JED and a direct consequence is a jet torque largely dominating the viscuous torque. This in turn implies an accretion velocity of the order of the sound speed and then a density much lower than a standard accretion disc. Moreover, most of the accretion power Pacc being extracted by the jet, only part of it (<50%) is liberated in the JED as heating power.

Evolution of the disc radii during outburst of X-ray binaries as infered from thermal emission.

Compact object displays drastic spectral and timing changi ng from the beginning to the end of an outburst, showing the different efficiencies of accretio n processes. Black hole binaries hence exhibit schematically two different states in X-ray spectr a: he first dominated by a thermal component and the second by a hard powerlaw shape like. Whereas th hard component is often attributed to the emission of a radiatively inefficient coro na, the thermal component is interpreted as the emission of the optically thick accretion disc. The commonly accepted picture suggests that the observed tr ansition between hard and soft states is associated by a drop in the accretion efficiency of the ther mal component by a recession of the internal disc radius in hard states. However, recent studie s based on relativistically broadened iron line and the thermal component strength analysis would tend to show the presence of the disc in the vicinity of the horizon. By a reanalysis of archive spect ra where thermal emission is present, we tracked the values of the disc radii during outbursts amon g several sources. Indeed, whereas a constant inner radius would imply that the disc luminosity s hould monotonically depends on the temperature, we show that this relationship seems to deviat e at the lowest luminosities.

A multi‐flow model for microquasars

We present a unified picture to explain the spectral states of BH binaries. In our view, the central regions have a multi‐flow configuration consisting in (1) an outer standard accretion disc (SAD) down to a transition radius rtr, (2) an inner magnetized jet emitting disc (JED) below rtr driving (3) a self‐collimated non relativistic MHD jet surrounding, when conditions for pair creation are met, (4) a ultra relativistic pair beam. Large values of rtr correspond to Hard states while small values correspond to Soft states. In between these extremes, in the high intermediate state, rtr can reach values that switch on a pair cascade process giving birth to ultra‐relativistic pair blobs that explain the superluminal events. The nature of the X‐ray variability in the hard state is also investigated by assuming an oscillating hot plasma at the jet basis whose temperature and density vary locally through the propagation of a magnetosonic wave. The variable comptonized spectra are computed through monte‐carlo sim...

A unified paradigm for the spectral and temporal evolution of Black Hole X-ray Binaries

We present a unified picture to explain the spectral states of BH binaries based on the two-flow model developed in our team since several years and already applied with success to AGNs. In our view, the central regions have a multi-flow configuration consisting in (1) an outer standard accretion disc (SAD) down to a transition radius rtr , (2) an inner magnetized jet emitting disc (JED) below rtr driving (3) a self-collimated non relativistic MHD jet surrounding, when conditions for pair creation are met, (4) a ultra relativistic pair beam. Large values of rtr correspond to Hard states while small values correspond to Soft states. In between these extremes, in the high intermediate state, rtr can reach values that switch on a pair cascade process giving birth to ultra-relativistic pair blobs that explain the superluminal events. In this model the accretion rate but also the disc magnetization μ play important roles, the latter being necessarily in the range 0.1–1 for the MHD jet to exist. Then, with simple assumptions on μ , we propose an explanation for the hysteresis behavior observed in microquasars during their outburst . We also discuss the nature, in our framework, of the X-ray corona. While it is commonly believed to be at the base of the jet it cannot be in the jet itself, its optical depth being to small to be consistent with the X-ray spectra observed in the Hard state. We show that it is expected to form naturally in the JED itself. Finally we investigate the nature of the X-ray variability in the hard state by assuming an oscillating hot plasma whose temperature and density vary locally through the propagation of a magneto-sonic wave. The variable comptonized spectra are computed through Monte-Carlo simulation. Preliminary results are discussed.