Wind suppression by X-rays in Cygnus X-3

Context. The radiatively driven wind of the primary star in wind-fed X-ray binaries can be suppressed by the X-ray irradiation of the compact secondary star. This causes feedback between the wind and the X-ray luminosity of the compact star.Aims. We aim to estimate how the wind velocity on the face-on side of the donor star depends on the spectral state of the high-mass X-ray binary Cygnus X-3.Methods. We modeled the supersonic part of the wind by computing the line force (force multiplier) with the Castor, Abbott & Klein formalism and XSTAR physics and by solving the mass conservation and momentum balance equations. We computed the line force locally in the wind considering the radiation fields from both the donor and the compact star in each spectral state. We solved the wind equations at different orbital angles from the line joining the stars and took the effect of wind clumping into account. Wind-induced accretion luminosities were estimated using the Bondi-Hoyle-Lyttleton formalism and computed wind velocities at the compact star. We compared them to those obtained from observations.Results. We found that the ionization potentials of the ions contributing the most to the line force fall in the extreme-UV region (100-230 angstrom). If the flux in this region is high, the line force is weak, and consequently, the wind velocity is low. We found a correlation between the luminosities estimated from the observations for each spectral state of Cyg X-3 and the computed accretion luminosities assuming moderate wind clumping and a low mass of the compact star. For high wind clumping, this correlation disappears. We compared the XSTAR method used here with the comoving frame method and found that they agree reasonably well with each other.Conclusions. We show that soft X-rays in the extreme-UV region from the compact star penetrate the wind from the donor star and diminish the line force and consequently the wind velocity on the face-on side. This increases the computed accretion luminosities qualitatively in a similar manner as observed in the spectral evolution of Cyg X-3 for a moderate clumping volume filling factor and a compact star mass of a few (2-3) solar masses.Peer reviewe

Multi-wavelength INTEGRAL NEtwork (MINE) observations of the microquasar GRS 1915+105

We present the international collaboration MINE (Multi-lambda Integral NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will focus on the 2003 March-April campaign of observations of the peculiar microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was observed 3 times in the plateau state, before and after a major radio and X-ray flare. It showed strong steady optically thick radio emission corresponding to powerful compact jets resolved in the radio images, bright near-infrared emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without cutoff in the 3-300 keV range. We compare the different observations, their multi-wavelength light curves, including JEM-X, ISGRI and SPI, and the parameters deduced from fitting the spectra obtained with these instruments on board INTEGRAL.Comment: 4 pages, 9 fig., Proc. of the 5th INTEGRAL Workshop (Feb. 16-20 2004), to be published by ES

Simultaneous multi-wavelength observations of microquasars (the MINE collaboration)

We present the international collaboration MINE (Multi-lambda INTEGRAL NEtwork) aimed at conducting multi-wavelength observations of microquasars simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105 are encouraging and those to come should help us to understand the physics of the accretion and ejection phenomena around a compact object.Comment: 2 p, 3 fig., proc. of the IAU Coll. 194, ``Compact Binaries in the Galaxy and Beyond'', Nov. 2003, La Paz, Mexico, to be published in the Conf. Series of Revista Mexicana de Astronomia y Astrofisica, Eds. G. Tovmassian & E. Sio

Multiwavelength Observations of GX 339-4 in 1996. I. Daily Light Curves and X-ray and Gamma-Ray Spectroscopy

As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present our radio, X-ray, and gamma-ray observations made in July, when the source was in a hard state (= soft X-ray low state). The radio observations were made at the time when there was a possible radio jet. We show that the radio spectrum was flat and significantly variable, and that the radio spectral shape and amplitude at this time were not anomalous for this source. Daily light curves from our pointed observation July 9-23 using OSSE, from BATSE, and from the ASM on RXTE also show that there was no significant change in the X- and gamma-ray flux or hardness during the time the possible radio jet-like feature was seen. The higher energy portion of our pointed RXTE observation made July 26 can be equally well fit using simple power law times exponential (PLE) and Sunyaev-Titarchuk (ST) functions. An additional soft component is required, as well as a broad emission feature centered on 6.4 keV. This may be an iron line that is broadened by orbital Doppler motions and/or scattering off a hot medium. Its equivalent width is 600 eV. Our simplistic continuum fitting does not require an extra reflection component. Both a PLE and a ST model also fit our OSSE spectrum on its own. Although the observations are not quite simultaneous, combining the RXTE and CGRO spectra we find that the PLE model easily fits the joint spectrum. However, the ST model drops off too rapidly with increasing energies to give an acceptable joint fit.Comment: Submitted to Astrophysical Journal. 25 pages. 11 figure

Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations

We report on the analysis of 100 ks INTEGRAL observations of the Galactic microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the source was found to exhibit a new type of variability as preliminarily reported in Hannikainen et al. (2003). The variability pattern, which we name $\xi$, is characterized by a pulsing behaviour, consisting of a main pulse and a shorter, softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a study of the individual RXTE/PCA pulse profiles we find that the rising phase is shorter and harder than the declining phase, which is opposite to what has been observed in other otherwise similar variability classes in this source. The position in the colour-colour diagram throughout the revolution corresponds to State A (Belloni et al. 2000) but not to any previously known variability class. We separated the INTEGRAL data into two subsets covering the maxima and minima of the pulses and fitted the resulting two broadband spectra with a hybrid thermal--non-thermal Comptonization model. The fits show the source to be in a soft state characterized by a strong disc component below ~6 keV and Comptonization by both thermal and non-thermal electrons at higher energies.Comment: Accepted for publication in A&A. 11 pages, 10 figures, 4 in colour. Original figures can be found at http://www.astro.helsinki.fi/~diana/grs1915_rev48. Author affiliations correcte

Two years of INTEGRAL monitoring of GRS 1915+105 Part 1: multiwavelength coverage with INTEGRAL, RXTE, and the Ryle radio Telescope

(Abridged) We report the results of monitoring observations of the Galactic microquasar GRS 1915+105 performed simultaneously with INTEGRAL and RXTE Ryle . We present the results of the whole \integral campaign, report the sources that are detected and their fluxes and identify the classes of variability in which GRS 1915+105 is found. The accretion ejection connections are studied in a model independent manner through the source light curves, hardness ratio, and color color diagrams. During a period of steady ``hard'' X-ray state (the so-called class chi) we observe a steady radio flux. We then turn to 3 particular observations during which we observe several types of soft X-ray dips and spikes cycles, followed by radio flares. During these observations GRS 1915+105 is in the so-called nu, lambda, and beta classes of variability. The observation of ejections during class lambda are the first ever reported. We generalize the fact that a (non-major) discrete ejection always occurs, in GRS 1915+105, as a response to an X-ray sequence composed of a spectrally hard X-ray dip terminated by an X-ray spike marking the disappearance of the hard X-ray emission above 18 keV. We also identify the trigger of the ejection as this X-ray spike. A possible correlation between the amplitude of the radio flare and the duration of the X-ray dip is found in our data. In this case the X-ray dips prior to ejections could be seen as the time during which the source accumulates energy and material that is ejected later.Comment: 17 pages, 14 figures. Accepted for publication in ApJ, scheduled for the March 20, 2008, vol676 issue. Table 3 has been degrade

The Hardness-Intensity Diagram of Cygnus X-3: Revisiting the Radio/X-Ray States

Cygnus X-3 is one of the brightest X-ray and radio sources in the Galaxy, and is well known for its erratic behaviour in X-rays as well as in the radio, occasionally producing major radio flares associated with relativistic ejections. However, even after many years of observations in various wavelength bands Cyg X-3 still eludes clear physical understanding. Studying different emission bands simultaneously in microquasars has proved to be a fruitful approach towards understanding these systems, especially by shedding light on the accretion disc/jet connection. We continue this legacy by constructing a hardness-intensity diagram (HID) from archival Rossi X-ray Timing Explorer data and linking simultaneous radio observations to it. We find that surprisingly Cyg X-3 sketches a similar shape in the HID to that seen in other transient black hole X-ray binaries during outburst but with distinct differences. Together with the results of this analysis and previous studies of Cyg X-3 we conclude that the X-ray states can be assigned to six distinct states. This categorization relies heavily on the simultaneous radio observations and we identify one new X-ray state, the hypersoft state, similar to the ultrasoft state, which is associated to the quenched radio state during which there is no or very faint radio emission. Recent observations of GeV flux observed from Cyg X-3 (Tavani et al. 2009; Fermi LAT Collaboration et al. 2009) during a soft X-ray and/or radio quenched state at the onset of a major radio flare hint that a very energetic process is at work during this time, which is also when the hypersoft X-ray state is observed. In addition, Cyg X-3 shows flaring with a wide range of hardness.Comment: 17 pages, 9 figures, accepted for publication in MNRA

Broadband X-ray spectrum of XTE J1550-564 during 2003 outburst

Results of broadband INTEGRAL and RXTE observations of the Galactic microquasar XTE J1550-564 during outburst in spring 2003 are presented. During the outburst the source was found in a canonical low/hard spectral state.Comment: 5 pages, 3 figures. Accepted for publication in Astronomy Letter

Sources of Relativistic Jets in the Galaxy

Black holes of stellar mass and neutron stars in binary systems are first detected as hard X-ray sources using high-energy space telescopes. Relativistic jets in some of these compact sources are found by means of multiwavelength observations with ground-based telescopes. The X-ray emission probes the inner accretion disk and immediate surroundings of the compact object, whereas the synchrotron emission from the jets is observed in the radio and infrared bands, and in the future could be detected at even shorter wavelengths. Black-hole X-ray binaries with relativistic jets mimic, on a much smaller scale, many of the phenomena seen in quasars and are thus called microquasars. Because of their proximity, their study opens the way for a better understanding of the relativistic jets seen elsewhere in the Universe. From the observation of two-sided moving jets it is inferred that the ejecta in microquasars move with relativistic speeds similar to those believed to be present in quasars. The simultaneous multiwavelength approach to microquasars reveals in short timescales the close connection between instabilities in the accretion disk seen in the X-rays, and the ejection of relativistic clouds of plasma observed as synchrotron emission at longer wavelengths. Besides contributing to a deeper comprehension of accretion disks and jets, microquasars may serve in the future to determine the distances of jet sources using constraints from special relativity, and the spin of black holes using general relativity.Comment: 39 pages, Tex, 8 figures, to appear in vol. 37 (1999) of Annual Reviews of Astronomy and Astrophysic