Abstract: Based on a spectral analysis of the X-ray continuum that employs a fully relativistic accretion disk model, we conclude that the compact primary of the binary X-ray source GRS 1915+105 is a rapidly rotating Kerr black hole. We find a lower limit on the dimensionless spin parameter of a* > 0.98. Our result is robust in the sense that it is independent of the details of the data analysis and insensitive to the uncertainties in the mass and distance of the black hole. Furthermore, our accretion disk model includes an advanced treatment of spectral hardening. Our data selection relies on a rigorous and quantitative definition of the thermal state of black hole binaries, which we used to screen all of the available RXTE and ASCA data for the thermal state of GRS 1915+105. In addition, we focus on those data for which the accretion disk luminosity is less than 30% of the Eddington luminosity. We argue that these low-luminosity data are most appropriate for the thin α-disk model that we employ. We assume that there is zero torque at the inner edge of the disk, as is likely when the disk is thin, although we show that the presence of a significant torque does not affect our results. Our model and the model of the relativistic jets observed for this source constrain the distance and black hole mass and could thus be tested by determining a VLBA parallax distance and improving the measurement of the mass function. Finally, we comment on the significance of our results for relativistic jet and core-collapse models and for the detection of gravitational waves.

Abstract: We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Mergings of compact-star binaries are expected to be the most important sources for forthcoming gravitational-wave (GW) astronomy. In the first part of the review, we discuss observational manifestations of close binaries with NS and/or BH components and their merger rate, crucial points in the formation and evolution of compact stars in binary systems, including the treatment of the natal kicks, which NSs and BHs acquire during the core collapse of massive stars and the common envelope phase of binary evolution, which are most relevant to the merging rates of NS-NS, NS-BH and BH-BH binaries. The second part of the review is devoted mainly to the formation and evolution of binary WDs and their observational manifestations, including their role as progenitors of cosmologically-important thermonuclear SN Ia. We also consider AM CVn-stars, which are thought to be the best verification binary GW sources for future low-frequency GW space interferometers.

Abstract: The fluctuating-accretion model of Lyubarskii and its extension by Kotov, Churazov & Gilfanov seek to explain the spectral-timing properties of the X-ray variability of accreting black holes in terms of inward-propagating mass accretion fluctuations produced at a broad range of radii. The fluctuations modulate the X-ray emitting region as they move inwards and can produce temporal-frequency-dependent lags between energy bands, and energy-dependent power spectral densities (PSDs) as a result of the different emissivity profiles, which may be expected at different X-ray energies. Here, we use a simple numerical implementation to investigate in detail the X-ray spectral-timing properties of the model and their relation to several physically interesting parameters, namely the emissivity profile in different energy bands, the geometrical thickness and viscosity parameter of the accretion flow, the strength of damping on the fluctuations and the temporal coherence (measured by the 'quality factor', Q) of the fluctuations introduced at each radius. We find that a geometrically thick flow with large viscosity parameter is favoured, and we confirm that the predicted lags are quite robust to changes in the emissivity profile and physical parameters of the accretion flow, which may help to explain the similarity of the lag spectra in the low/hard and high/soft states of Cyg X-1. We also demonstrate the model regime where the light curves in different energy bands are highly spectrally coherent. We compare model predictions directly to X-ray data from the narrow line Seyfert 1 galaxy NGC 4051 and the black hole X-ray binary (BHXRB) Cyg X -1 in its high/soft state, and we show that this general scheme can reproduce simultaneously the time lags and energy-dependence of the PSD.

Abstract: We present a new edition of the catalogue of high-mass X-ray binaries in the Galaxy. The catalogue contains source name(s), coordinates, finding chart, X-ray luminosity, system parameters, and stellar parameters of the components and other characteristic properties of 114 high-mass X-ray binaries, together with a comprehensive selection of the relevant literature. The aim of this catalogue is to provide the reader with some basic information on the X-ray sources and their counterparts in other wavelength ranges (gamma-rays, UV, optical, IR, radio). About 60% of the high-mass X-ray binary candidates are known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries. Some sources, however, are only tentatively identified as high-mass X-ray binaries on the basis of their X-ray properties similar to the known high-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the high-mass nature of the X-ray binary this is mentioned. Literature published before 1 October 2005 has, as far as possible, been taken into account.

Abstract: Context. LS 5039 and LS 1+61°303 are unique amongst high-mass X-ray binaries (HMXB) for their spatially-resolved radio emission and their counterpart at >GeV gamma-ray energies, canonically attributed to non-thermal particles in an accretion-powered relativistic jet. The only other HMXB known to emit very high-energy (VHE) gamma-rays, PSR B 1259-63, harbours a non-accreting millisecond pulsar. Aims. The purpose is to investigate whether the interaction of the relativistic wind from a young pulsar with the wind from its stellar companion, as in PSR B1259-63, constitutes a viable scenario for explaining the observations of LS 5039 and LSI+61°303. Emission arises from the shocked pulsar wind material, which then flows away to large distances in a comet-shape tail, reproducing on a smaller scale what is observed in isolated, high motion pulsars interacting with the interstellar medium. Methods. The timescales for acceleration and radiation of particles at the shock between the pulsar wind and stellar wind are calculated. Simple expectations for the spectral energy distribution (SED) are derived and are shown to depend on very few input parameters. Detailed modelling of the particle evolution is attempted and compared to the observations from radio to TeV energies. Results. Acceleration at the shock provides high-energy electrons that steadily emit synchrotron in X-rays and inverse Compton scatter stellar light to γ-rays. Electrons streaming out of the system emit at IR frequencies and below. The overall aspect of the SEDs is adequately reproduced for standard values of the parameters. The morphology of the radio tail can mimic a microquasar jet. Good agreement is found with the published VLBI map of LS 5039 and predictions are made on the expected change in appearance with orbital phase. Conclusions. The pulsar wind scenario provides a common, viable framework for interpreting the emission from all three γ-ray binaries.

Abstract: We present an analysis of 13 of the best quality ultraluminous X-ray source (ULX) data sets available from XMM‐Newton European Photon Imaging Camera (EPIC) observations. We utilize the high signal-to-noise in these ULX spectra to investigate the best descriptions of their spectral shape in the 0.3‐10 keV range. Simple models of an absorbed power law or multicolour disc blackbody prove inadequate at describing the spectra. Better fits are found using a combination of these two components, with both variants of this model ‐ a cool (∼0.2 keV) disc blackbody plus hard power-law continuum, and a soft power-law continuum, dominant at low energies, plus a warm (∼1.7 keV) disc blackbody ‐ providing good fits to 8/13 ULX spectra. However, by examining the data above 2 keV, we find evidence for curvature in the majority of data sets (8/13 with at least marginal detections), inconsistent with the dominance of a power law in this regime. In fact, the most successful empirical description of the spectra proved to be a combination of a cool (∼0.2 keV) classic blackbody spectrum, plus a warm disc blackbody that fits acceptably to 10/13 ULXs. The best overall fits are provided by a physically self-consistent accretion disc plus Comptonized corona model (DISKPN + EQPAIR), which fits acceptably to 11/13 ULXs. This model provides a physical explanation for the spectral curvature, namely that it originates in an optically thick corona, though the accretion disc photons seeding this corona still originate in an apparently cool disc. We note similarities between this fit and models of Galactic black hole binaries at high accretion rates, most notably the model of Done & Kubota. In this scenario the inner disc and corona become energetically coupled at high accretion rates, resulting in a cooled accretion disc and optically thick corona. We conclude that this analysis of the best spectral data for ULXs shows it to be plausible that the majority of the population are high accretion rate stellar-mass (perhaps up to 80 M� ) black holes, though we cannot categorically rule out the presence of larger,

Abstract: We present the first results of coordinated multiwavelength observations of the Galactic black hole GX 339-4 in a canonical low/hard state, obtained during its 2004 outburst. XMM-Newton observed the source for two revolutions, or approximately 280 ks; RXTE monitored the source throughout this long stare. The resulting data offer the best view yet obtained of the inner accretion flow geometry in the low/hard state, which is thought to be analogous to the geometry in low-luminosity active galactic nuclei. The XMM-Newton spectra clearly reveal the presence of a cool accretion disk component and a relativistic Fe K emission line. The results of fits made to both components strongly suggest that a standard thin disk remains at or near to the innermost stable circular orbit, at least in bright phases of the low/hard state. These findings indicate that potential links between the inner disk radius and the onset of a steady compact jet, and the paradigm of a radially recessed disk in the low/hard state, do not hold universally. The results of our observations can best be explained if a standard thin accretion disk fuels a corona that is closely related to, or consistent with, the base of a compact jet. In a brief examination of archival data, we show that Cygnus X-1 supports this picture of the low/hard state. We discuss our results within the context of disk-jet connections and prevailing models for accretion onto black holes.

Abstract: Deep observations with the Very Large Array of A0620-00, performed in 2005 August, resulted in the first detection of radio emission from a black hole binary at X-ray luminosities as low as 10-8.5 times the Eddington limit. The measured radio flux density, of 51 +/- 7 ?Jy at 8.5 GHz, is the lowest reported for an X-ray binary system so far, and is interpreted in terms of partially self-absorbed synchrotron emission from outflowing plasma. Making use of the estimated outer accretion rate of A0620-00 in quiescence, we demonstrate that the outflow kinetic power must be energetically comparable to the total accretion power associated with such rate, if it was to reach the black hole with the standard radiative efficiency of 10 per cent. This favours a model for quiescence in which a radiatively inefficient outflow accounts for a sizable fraction of the missing energy, and, in turn, substantially affects the overall dynamics of the accretion flow. Simultaneous observations in the X-ray band, with Chandra, confirm the validity of a non-linear radio/X-ray correlation for hard state black hole binaries down to low quiescent luminosities, thereby contradicting some theoretical expectations. Taking the mass term into account, the A0620-00 data lie on the extrapolation of the so-called Fundamental Plane of black hole activity, which has thus been extended by more than two orders of magnitude in radio and X-ray luminosity. With the addition of the A0620-00 point, the plane relation provides an empirical proof for the scale invariance of the jet-accretion coupling in accreting black holes over the entire parameter space observable with current instrumentation.

Abstract: The optical/near-infrared (OIR) region of the spectra of low-mass X-ray binaries appears to lie at the intersection of a variety of different emission processes. In this paper we present quasi-simultaneous OIR–X-ray observations of 33 XBs in an attempt to estimate the contributions of various emission processes in these sources, as a function of X-ray state and luminosity. A global correlation is found between OIR and X-ray luminosity for low-mass black hole candidate XBs (BHXBs) in the hard X-ray state, of the form LOIR / L 0.6 X . This correlation holds over 8 orders of magnitude in LX and includes data from BHXBs in quiescence and at large distances (LMC and M31). A similar correlation is found in low-mass neutron star XBs (NSXBs) in the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and some of the optical emission is suppressed below the correlation, a behaviour indicative of the jet switching off/on in transition to/from the soft state. We compare these relations to theoretical models of a number of emission processes. We find that X-ray reprocessing in the disc and emission from the jets both predict a slope close to 0.6 for BHXBs, and both contribute to the OIR in BHXBs in the hard state, the jets producing � 90 percent of the NIR emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in the hard state, with possible contributions from the jets (only at high luminosity) and the viscously heated disc. We also show that the optically thick jet spectrum of BHXBs extends to near the K-band. OIR spectral energy distributions of 15 BHXBs help us to confirm these interpretations. We present a prediction of the LOIR–LX behaviour of a BHXB outburst that enters the soft state, where the peak LOIR in the hard state rise is greater than in the hard state decline (the well known hysteretical behaviour). In addition, it is possible to estimate the X-ray, OIR and radio luminosity and the mass accretion rate in the hard state quasi-simultaneously, from observations of just one of these wavebands, since they are all linked through correlations. Finally, we have discovered that the nature of the compact object, the mass of the companion and the distance/reddening can be constrained by quasi-simultaneous OIR and X-ray luminosities.

Abstract: New observations of LS 5039, a High Mass X-ray Binary comprising a massive star and compact object, were carried out with the High Energy Stereoscopic System of Cherenkov Telescopes (HESS) in 2005 at very high energy (VHE) gamma-ray energies These observations reveal that its flux and energy spectrum are modulated with the 39 day orbital period of the binary system This is the first time in gamma-ray astronomy that orbital modulation has been observed, and periodicity clearly established using ground-based gamma-ray detectors The VHE gamma-ray emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object For this epoch, there is also a hardening of the energy spectrum in the energy range between 02 TeV and a few TeV The flux vs orbital phase profile provides the first clear indication of gamma-ray absorption via pair production within an astrophysical source, a process which is expected to occur if the gamma-ray production site is situated within ~1 AU of the compact object Moreover the production region size must be not significantly greater than the binary separation (~015 AU) Notably, these constraints are also considerably smaller than the collimated outflows or jets (extending out to ~1000 AU) observed in LS 5039 The spectral hardening could arise from variations with phase in the maximum electron energies, and/or the dominant VHE gamma-ray production mechanism

Abstract: The periodic precession (162–day) and nodding (6.3–day) motions of the jets in SS433 are driven in the outer regions of the disc, whereas the jets themselves, being relativistic, are launched near the black hole at the disc centre. Given that the nutation period is comparable to the dynamical timescale in the outer regions of the disc, it seems unlikely that these periods can be communicated efficiently to the disc centre. Here we propose that the massive outflow observed in SS433 is launched at large radii in the disc, about 1/10 of the outer disc edge, and that it is this outflow which responds to the oscillations of the outer disc and determines the direction of the jets. The massive outflow is launched at large radius because the mass transfer rate is hyper-Eddington. This implies not only that the total luminosity of SS433 exceeds LEdd by a considerable factor, but also that the radiative output is collimated along the outflow. We thus suggest that SS433 is an ultraluminous X–ray source (ULX) viewed ‘from the side’. We also suggest that the obscured INTEGRAL sources may be SS433–like objects, but with slightly lower mass transfer rates.

Abstract: WepresentresultsfromspectralmodelingofthreeblackholeX-raybinaries:LMCX-3,GROJ1655� 40,andXTE J1550� 564. Using a sample of disk-dominated observations, we fit the data with a range of spectral models that in- cludes a simple multitemperature blackbody (DISKBB), a relativistic accretion disk model based on color-corrected blackbodies (KERRBB), and a relativistic model based on non-LTE atmosphere models within anprescription (BHSPEC). BHSPEC provides the best fit for a BeppoSAXobservation of LMC X-3, which has the broadest energy coverage of our sample. It also provides the best fit for multiple epochs of Rossi X-Ray Timing Explorer (RXTE) data in this source, except at the very highest luminosity (L/LEdd k0:7), where additional physics must be coming into play.BHSPECisalsothebest-fitmodelformultiepochRXTEobservationsofGROJ1655� 40andXTEJ1550� 564, although the best-fit inclination of the inner disk differs from the binary inclination. All our fits prefer � ¼ 0:01 to � ¼ 0:1, in apparent disagreement with the large stresses inferred from the rapid rise times observed in outbursts of these two sources. In all three sources our fits imply moderate black hole spins (a� � 0:1 0:8), but this is sensitive to the reliability of independent measurements of these system parameters and to the physical assumptions that un- derly our spectral models. Subject headingg accretion, accretion disks — black hole physics — X-rays: binaries

Abstract: Context. Gamma-ray emission in the TeV (10 12 eV) range has been detected by HESS from two X-ray binaries: PSR B1259-63 and LS 5039. In both, the early-type star provides large numbers of target photons for pair-production with TeV γ-rays. This results in a modulation of the γ-ray flux as the relative positions of the γ-ray source and companion star change with orbital phase for the observer. Aims. The extent to which this variable absorption can provide useful diagnostics for the location and nature of γ-ray emission is examined. Methods. The absorption spectrum and transmitted flux are calculated by integrating the yy cross-section along the line-of-sight, taking into account the orbit, the spectrum and the finite size of the companion star in LS 5039, PSR B1259-63 and LSI +61°303, a system similar to LS 5039 but still undetected at TeV energies. Results. In LS 5039, emission close to a black hole or a neutron star primary is considered. In both cases, the transmitted flux >250 GeV drops by an order-of-magnitude near periastron (0 = 0). A black hole yields a clear spectral signature in the average spectrum at ≈400 GeV. A neutron star yields more variability, with the spectral feature moving from 200 GeV (Φ = 0.1) to 3 TeV (Φ = 0.7). Only 20% of the flux is absorbed at Φ = 0.7, allowing for an almost direct view of the intrinsic spectrum. Low variability will require emission on large scales, more than 0.7 AU away to have <50% absorption in a jet. In LSI +61°303, significant absorption (up to 90% of the 100 GeV flux) is predicted only slightly before periastron, accompanied by a spectral hardening above 1 TeV. In PSR B1259-63, although 40% of the flux is absorbed before periastron, the large variability seen by HESS is due to the γ-ray emission process. Conclusions. The predictions made here are essential to distinguish variability in the emission of γ-rays from that due to absorption. A modulation would provide a novel way to constrain the γ-ray source. Its absence would imply that γ-ray emission occurs on large scales.

Abstract: Continuing the observational campaign initiated by our group, we present the long term spectral evolution of the Galactic black hole candidate Cygnus X-1 in the X-rays and at 15 GHz We present ∼200 pointed observations taken between early 1999 and late 2004 with the Rossi X-ray Timing Explorer and the Ryle radio telescope The X-ray spectra are remarkably well described by a simple broken power law spectrum with an exponential cutoff Physically motivated Comptonization models, eg, by Titarchuk (1994, ApJ, 434, 570, compTT) and by Coppi (1999, in High Energy Processes in Accreting Black Holes, ed J Poutanen, & R Svensson (San Francisco: ASP), ASP Conf Ser, 161, 375, eqpair), can reproduce this simplicity; however, the success of the phenomenological broken power law models cautions against “overparameterizing” the more physical models Broken power law models reveal a significant linear correlation between the photon index of the lower energy power law and the hardening of the power law at ∼10 keV This phenomenological soft/hard power law correlation is partly attributable to correlations of broad band continuum components, rather than being dominated by the weak hardness/reflection fraction correlation present in the Comptonization model Specifically, the Comptonization models show that the bolometric flux of a soft excess (eg, disk component) is strongly correlated with the compactness ratio of the Comptonizing medium, with L disk ∝( h / s ) −019 Over the course of our campaign, Cyg X-1 transited several times into the soft state, and exhibited a large number of “failed state transitions” The fraction of the time spent in such low radio emission/soft X-ray spectral states has increased from ∼10% in 1996–2000 to ∼34% since early 2000 We find that radio flares typically occur during state transitions and failed state transitions (at h / s ∼ 3), and that there is a strong correlation between the 10–50 keV X-ray flux and the radio luminosity of the source We demonstrate that rather than there being distinctly separated states, in contrast to the timing properties the spectrum of Cyg X-1 shows variations between extremes of properties, with clear cut examples of spectra at every intermediate point in the observed spectral correlations

Abstract: We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r J ; (2) an inner magnetized accretion disc below r J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met; (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/γ -rays, by varying the transition radius r J and disc accretion rate independently. Large values of r J correspond to the Quiescent state for low and the Hard state for larger . These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r J . The hard X-ray component is expected to form at the jet basis. When r I becomes smaller than the marginally stable orbit r i , the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where . At large , an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, sometimes referred to as the Very High state, with its associated superluminal motions. The variation of r J independently of is a necessary ingredient in this picture. It arises from the presence of a large scale vertical magnetic field threading the disc. Features such as possible hysteresis and the presence of quasi-periodic oscillations would naturally fit within this new framework.

Abstract: Approximate analytical formulae are derived for the pulse profile produced by small hotspots on a rapidly rotating neutron star. Its Fourier amplitudes and phases are calculated. The proposed formalism takes into account gravitational bending of light, Doppler effect, anisotropy of emission and time delays. Its accuracy is checked with exact numerical calculations.

Abstract: the date of receipt and acceptance should be inserted later Abstract. Observational and theoretical studies point to microquasars (MQs) as possible counterparts of a significant fraction of the unidentified gamma-ray sources detected so far. At present, a proper scenario to explain the emission beyond soft X-rays from these objects is not known, nor what the precise connection is between the radio and the high-energy radiation. We develop a new model where the MQ jet is dynamically dominated by cold protons and radiatively dominated by relativistic leptons. The matter content and power of the jet are both related with the accretion process. The magnetic field is assumed to be close to equipartition, although it is attached to and dominated by the jet matter. For the relativistic particles in the jet, their maximum energy depends on both the acceleration efficiency and the energy losses. The model takes into account the interaction of the relativistic jet particles with the magnetic field and all the photon and matter fields. Such interaction produces significant amounts of radiation from radio to very high energies through synchrotron, relativistic Bremsstrahlung, and inverse Compton (IC) processes. Variability of the emission produced by changes in the accretion process (e.g. via orbital eccentricity) is also expected. The effects of the gamma-ray absorption by the external photon fields on the gamma-ray spectrum have been taken into account, revealing clear spectral features that might be observed. This model is consistent to the accretion scenario, energy conservation laws, and current observational knowledge, and can provide deeper physical information of the source when tested against multiwavelength data.

Abstract: PSR B1259−63 is in a highly eccentric 3.4-yr orbit with a Be star and crosses the Be star disc twice per orbit, just prior to and just after periastron. Unpulsed radio, X-ray and gamma-ray emission observed from the binary system is thought to be due to the collision of pulsar wind with the wind of Be star. We present here the results of new XMM–Newton observations of the PSR B1259−63 system during the beginning of 2004 as the pulsar approached the disc of the Be star. We combine these results with the earlier unpublished X-ray data from BeppoSAX and XMM–Newton as well as with the ASCA data. The detailed X-ray light curve of the system shows that the pulsar passes (twice per orbit) through a well-defined Gaussian-profile disc with the half-opening angle (projected on the pulsar orbit plane) . The intersection of the disc middle plane with the pulsar orbital plane is inclined at θdisc≃ 70° to the major axis of the pulsar orbit. Comparing the X-ray light curve to the TeV light curve of the the system, we find that the increase of the TeV flux some 10–100 d after the periastron passage is unambiguously related to the disc passage. At the moment of entrance to the disc, the X-ray photon index hardens from Γ≃ 1.8 up to ≃1.2 before returning to the steeper value Γ≥ 1.5. Such behaviour is not easily accounted for by the model in which the X-ray emission is synchrotron emission from the shocked pulsar wind. We argue that the observed hardening of the X-ray spectrum is due to the inverse-Compton or bremsstrahlung emission from 10–100 MeV electrons responsible for the radio synchrotron emission.

Abstract: Microquasars are galactic black hole binary systems with radio jets which can sometimes be spatially resolved to show superluminal motion. The first and best known of this class of objects is GRS 1915+105, the brightest accreting source in our Galaxy. There is persistent speculation that strong jet emission could be linked to black hole spin. If so, the high spin should also be evident in accretion disc spectra. We search the RXTE archive to find disc-dominated X-ray spectra from this object, as these are the only ones which can give reliable spin determinations by this method. Finding these is complicated by the rapid, unique limit cycle variability, but we are able to identify such spectra by going to the shortest possible time resolution (16 s). We fit them with a simple multicolour disc blackbody (DISKBB), and with the best current model which include full radiative transfer as well as relativistic effects (BHSPEC). Both these models show that the spin is intermediate, neither zero nor maximal. BHSPEC, the most physical model, gives a value for the dimensionless spin of a* ∼0.7 for a distance of 12.5 kpc and inclination of 66°. This, together with the range of spins 0.1 < a· < 0.8 derived using this method for other black holes, suggests that jet emission is probably fundamentally powered by gravity rather than spin, and implies that high-to-maximal spin is not a pre-requisite for powerful relativistic jets.

Abstract: We use a relativistic ray-tracing code to calculate the light curves observed from a global, general relativistic, magnetohydrodynamic simulation of an accretion flow onto a Schwarzschild black hole. We apply three basic emission models to sample different properties of the time-dependent accretion disk. With one of these models, which assumes thermal blackbody emission and free-free absorption, we can predict qualitative features of the high-frequency power spectrum from stellar-mass black holes in the "thermal dominant" state. The simulated power spectrum is characterized by a power law of index Γ ≈ 3 and total rms fractional variance of 2% above 10 Hz. For each emission model, we find that the variability amplitude should increase with increasing inclination angle. On the basis of a newly developed formalism for quantifying the significance of quasi-periodic oscillations (QPOs) in simulation data, we find that these simulations are able to identify any such features with (rms/mean) amplitudes 1% near the orbital frequency at the innermost stable orbit. Initial results indicate the existence of transient QPO peaks with frequency ratios of nearly 2 : 3 at a 99.9% confidence limit, but they are not generic features, because at any given time they are seen only from certain observer directions. In addition, we present detailed analysis of the azimuthal structure of the accretion disk and the evolution of density perturbations in the inner disk. These "hot-spot" structures appear to be roughly self-similar over a range of disk radii, with a single characteristic size δ = 25° and δr/r = 0.3, and typical lifetimes Tl ≈ 0.3Torb.

Abstract: The INTEGRAL satellite extensively observed the black hole binary Cygnus X-1 from 2002 November to 2004 November during calibration, open time and core program (Galactic Plane Scan) observations. These data provide evidence for significant spectral variations over the period. In the framework of the accreting black hole phenomenology, the source was most of the time in the Hard State and occasionally switched to the so-called "Intermediate State". Using the results of the analysis performed on these data, we present and compare the spectral properties of the source over the whole energy range (5 keV-1 MeV) covered by the high-energy instruments on board INTEGRAL, in both observed spectral states. Fe line and reflection component evolution occurs with spectral changes in the hard and soft components. The observed behaviour of Cygnus X-1 is consistent with the general picture of galactic black holes. Our results give clues to the physical changes that took place in the system (disc and corona) at almost constant luminosity during the spectral transitions and provide new measures of the spectral model parameters. In particular, during the Intermediate State of 2003 June, we observe in the Cygnus X-1 data a high-energy tail at several hundred keV in excess of the thermal Comptonization model which suggests the presence of an additional non-thermal component.

Abstract: We perform binary population-synthesis calculations to investigate the incidence of low-mass X-ray binaries (LMXBs) and their birth rate in the Galaxy. We use a binary-evolution algorithm that models all the relevant processes including tidal circularization and synchronization. Parameters in the evolution algorithm that are uncertain and may affect X-ray binary formation are allowed to vary during the investigation. We agree with previous studies that under standard assumptions of binary evolution the formation rate and number of black hole (BH) LMXBs predicted by the model are more than an order of magnitude less than what is indicated by observations. We find that the common-envelope process cannot be manipulated to produce significant numbers of BH LMXBs. However, by simply reducing the mass-loss rate from helium stars adopted in the standard model, to a rate that agrees with the latest data, we produce a good match to the observations. Including LMXBs that evolve from intermediate-mass systems also leads to favourable results. We stress that constraints on the X-ray binary population provided by observations are used here merely as a guide as surveys suffer from incompleteness and much uncertainty is involved in the interpretation of results.

Abstract: We present the results of a systematic exploration of an alternative evolutionary scenario to form double neutron star (DNS) binaries, first proposed by Brown (1995), which does not involve a neutron star passing through a common envelope. In this scenario, the initial binary components have very similar masses, and both components have left the main sequence before they evolve into contact; preferably the primary has already developed a CO core. We have performed population synthesis simulations to study the formation of DNS binaries via this channel and to predict the orbital properties and system velocities of such systems. We obtain a merger rate for DNSs in this channel in the range of 0.1-12 Myr -1 . These rates are still subject to substantial uncertainties such as the modelling of the contact phase.

Abstract: We report the discovery with the RXTE PCA of twin kHz QPOs in the peculiar X-ray binary Circinus X-1. Eleven cases of simultaneous double QPOs occurred, with significances of up to 6.3 and 5.5 σ and centroid frequencies ranging between approximately 56 and 225 and 230 and 500 Hz for the two QPO peaks, respectively, i.e., for the most part at frequencies well below those of other sources. The QPO properties clearly indicate that these double peaks are the kHz QPOs known from low magnetic field neutron stars, and not black hole high-frequency QPOs, confirming that Cir X-1 is a neutron star, as suspected since the detection of type I X-ray bursts from the field of the source 20 years ago. The kHz QPO peak separation varies over a wide range, ~175-340 Hz, and increases as a function of kHz QPO frequency. This is contrary to what has been observed in other sources but in good agreement with predictions of the relativistic precession model and Alfven wave models; beat-frequency models require modification to accommodate this. In other observations, single kHz QPOs can be seen down to frequencies as low as ~12 Hz, as well as a strong low-frequency quasi-periodic oscillation (LF QPO) between 1 and 30 Hz. The relations between the kHz QPOs and the LF QPO are in good agreement with those found previously in Z sources, confirming that Cir X-1 may be a peculiar Z source. We suggest that the low-frequency range over which the kHz QPOs occur in Cir X-1 and to a lesser extent in (other) Z sources, might be due to a stronger radial accretion flow relative to the disk flow than in other kHz QPO sources, possibly related to the nature of the companion star.

Abstract: LSI +61 ◦ 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy gamma-ray emission have been observed. We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectra l index of the system. The X-ray spectrum is hard (photon index ≃ 1.5) during the orbital phases of both high and low X-ray flux. However, the spectrum softens at the moment of transition from high to low X-ray state. The spectrum of the system in the hard X-ray band does not reveal the presence of a cut-off (or, at least a spectral break) at 10-60 keV energies, expect ed if the compact object is an accreting neutron star. The observed spectrum and spectral variability can be explained if the compact object in the system is a rotation powered pulsar.

Abstract: There is growing evidence from both spectral and timing properties that there is a truncated inner accretion disc in low mass accretion rate Galactic black hole systems. The detection of extremely smeared relativistic iron lines in some of these systems is the only current piece of evidence which conflicts with this geometrical interpretation of the low/hard state. Here, we show that the line width in the BeppoSAX data of a bright low/hard state of the transient black hole XTE J1650−500 is indeed consistent with extreme relativistic effects. However, the relativistic smearing can be significantly reduced if there is also resonance iron K line absorption from an outflowing disc wind. The iron line smearing is then completely compatible with a truncated disc, so it gives no information on the black hole spin.

Abstract: Flat radio spectra with large brightness temperatures at the core of active galactic nuclei and X-ray binaries are usually interpreted as the partially self-absorbed bases of jet flows emitting synchrotron radiation. Here we extend previous models of jets propagating at large angles to our line of sight to self-consistently include the effects of energy losses of the relativistic electrons due to the synchrotron process itself and the adiabatic expansion of the jet flow. We also take into account energy gains through self-absorption. Two model classes are presented. The ballistic jet flows, with the jet material travelling along straight trajectories, and adiabatic jets. Despite the energy losses, both scenarios can result in flat emission spectra; however, the adiabatic jets require a specific geometry. No re-acceleration process along the jet is needed for the electrons. We apply the models to observational data of the X-ray binary Cygnus X-1. Both models can be made consistent with the observations. The resulting ballistic jet is extremely narrow with a jet opening angle of only 5 arcsec. Its energy transport rate is small compared to the time-averaged jet power and therefore suggests the presence of non-radiating protons in the jet flow. The adiabatic jets require a strong departure from energy equipartition between the magnetic field and the relativistic electrons. These models also imply a jet power of two orders of magnitude higher than the Eddington limiting luminosity of a 10-M ⊙ black hole. The models put strong constraints on the physical conditions in the jet flows on scales well below achievable resolution limits.

Abstract: We report the results of new SPH calculations of parabolic collisions between a subgiant or slightly evolved red giant star and a neutron star (NS). Such collisions are likely to provide the dominant formation mechanism for ultracompact X-ray binaries (UCXBs) observed today in old globular clusters. In particular, we compute collisions of a 1.4 M☉ NS with realistically modeled parent stars of initial masses 0.8 and 0.9 M☉, each at three different evolutionary stages (corresponding to three different core masses mc and radii R). The distance of closest approach for the initial orbit varies from rp = 0.04R (nearly head-on) to 1.3R (grazing). These collisions lead to the formation of a tight binary, composed of the NS and the subgiant or red giant core, embedded in an extremely diffuse common envelope (CE) typically of mass ~0.1-0.3 M☉. Our calculations follow the binary for many hundreds of orbits, ensuring that the orbital parameters we determine at the end of the calculations are close to final. Some of the fluid initially in the giant's envelope, from 0.003 to 0.023 M☉ in the cases we considered, is left bound to the NS. The eccentricities of the resulting binaries range from about 0.2 for our most grazing collision to about 0.9 for the nearly head-on cases. In almost all the cases we consider, gravitational radiation alone will cause sufficiently fast orbital decay to form a UCXB within a Hubble time, and often on a much shorter timescale. Our hydrodynamics code implements the recent SPH equations of motion derived with a variational approach by Springel & Hernquist and by Monaghan. Numerical noise is reduced by enforcing an analytic constraint equation that relates the smoothing lengths and densities of SPH particles. We present tests of these new methods to help demonstrate their improved accuracy.