Microquasar XTE J1550-564 Research Articles

Looking for the Elusive 3:2 Ratio of High-frequency Quasi-periodic Oscillations in the Microquasar XTE J1550−564

Abstract Using the two main XTE J1550−564 outbursts (1998–99 and 2000), we gathered about 30 observations with confirmed detections of high-frequency quasi-periodic oscillations (HFQPOs). While this is a small sample it is enough to start looking at the generic properties of these oscillations, especially focusing on their frequencies and their potential harmonic relationship. This then will provide us with a list of constraints, which are necessary for any attempt to model their origin. We defined five groups based on their similarities in the Fourier domain, namely the continuum of their power-density spectra (PDS) and the HFQPO frequencies. We then combined the individual PDS of each family to obtain a PDS with higher statistics to search for other potential, previously undetected, weaker peaks. While we have two 3σ potential detections of a pair of HFQPOs in our combined PDS, none of them show HFQPOs with frequencies in a previously claimed 3:2 ratio. Using the results presented here we propose an updated list of requirements for any model trying to explain the HFQPOs in microquasars.

Evolving morphology of the large-scale relativistic jets from XTE J1550−564

We present an in-depth study of the large-scale, western jet of the microquasar XTE J1550-564, based on X-ray and radio observations performed in 2002-2003. The jet is spatially resolved in both observing windows. The X-ray jet is expanding in time along the axis of the jet's propagation: we observe the formation of a tail (~2.25"), which appears to extend backwards with an apparent velocity ~-0.10c. The origin of this feature is discussed in the framework of scenarios of energy dissipation. A single power-law adequately describes the broadband spectra, supporting a synchrotron origin of the X-ray emission. However, a spectral break at ~10^{15} Hz is necessary in coincidence with a re-flare at 8.64 GHz in September 2002. This finding may be indicative of emission from newly accelerated low-energy particles. The first detection of the jet is in February 2001 (F_{8.64GHz}=0.25+/-0.09 mJy) in the flux rising phase. A phase of stable emission is followed by a rapid decay (t_{decay}=167+/-5 days). The decay at radio frequencies is significantly shorter than in X-rays (t_{decay}=338+/-14 days). We detected a high fraction (up to ~9%) of linearly polarized radiation at 4.8 GHz and 8.6 GHz. The orientation of the electric vector is consistent with the picture of a shock-compressed magnetic field, and there are hints of variations on month-timescales, possibly connected with the evolution of the jet structure.

Non-linear behaviour of XTE J1550-564 during its 1998−1999 outburst, revealed by recurrence analysis

We study the X-ray emission of the microquasar XTE J1550-564 and analyze the properties of its light curves using the recurrence analysis method. The indicators for non-linear dynamics of the accretion flow are found in the very high state and soft state of this source. The significance of deterministic variability depends on the energy band. We discuss the non-linear dynamics of the accretion flow in the context of the disc-corona geometry and propagating oscillations in the accretion flow.

Dynamic and spectral X-ray features of the microquasar XTE J1550-564

Memory function formalism is used to investigate the dynamic and spectral features (including a quantitative comparison of the decay of correlations and statistical memory) of the time discrete X-ray signals from the microquasar XTE J1550-564. The X-ray dynamics has been recorded aboard the Rossi X-Ray Timing Explorer. Temporal and event correlations are analyzed to find distinct patterns in the relaxation processes and memory effects in the equi- and nonequidistant dynamics of the X-ray flux from XTE J1550-564. The described method can be used to study a wide range of astrophysical phenomena and processes associated with event representation.

MODELING THE JET KINEMATICS OF THE BLACK HOLE MICROQUASAR XTE J1550–564: A CONSTRAINT ON SPIN-ORBIT ALIGNMENT

Measurements of black hole spin made using the continuum-fitting method rely on the assumption that the inclination of the black hole's spin axis to our line of sight is the same as the orbital inclination angle of the host binary system. The X=ray and radio jet data available for the microquasar XTE J1550-564 offer a rare opportunity to test this assumption. Following the work of others, we have modeled these data and thereby determined the inclination angle of the jet axis, which is presumed to be aligned with the black hole's spin axis. We find a jet inclination angle of approximately 71 degrees and place an upper limit on the difference between the spin and orbital inclinations of < 12 degrees (90% confidence). Our measurement tests for misalignment along the line of sight while providing no constraint perpendicular to this plane. Our constraint on the misalignment angle supports the prediction that the spinning black hole in XTE J1550-564 has aligned itself with the orbital plane and provides support for the measurement of its spin via the continuum-fitting method. Our conclusions are based on a simple and reasonable model of a pair of symmetric jets propagating into a low density cavity whose western wall is approximately 20% closer to XTE J1550-564 than its eastern wall.

The spin of the black hole microquasar XTE J1550−564 via the continuum-fitting and Fe-line methods

We measure the spin of XTE J1550-564 in two ways: by modelling the thermal continuum spectrum of the accretion disc, and independently by modeling the broad red wing of the reflection fluorescence Fe-K line. We find that the spin measurements conducted independently using both leading methods are in agreement with one another. For the continuum-fitting analysis, we use a data sample consisting of several dozen RXTE spectra, and for the Fe-K analysis, we use a pair of ASCA spectra from a single epoch. Our spin estimate for the black hole primary using the continuum-fitting method is -0.11 < a* < 0.71 (90 per cent confidence), with a most likely spin of a* = 0.34. In obtaining this result, we have thoroughly explored the dependence of the spin value on a wide range of model-dependent systematic errors and observational errors; our precision is limited by uncertainties in the distance and orbital inclination of the system. For the Fe-line method, our estimate of spin is a* = 0.55(+0.15,-0.22). Combining these results, we conclude that the spin of this black hole is moderate, a* = 0.49(+0.13,-0.20), which suggests that the jet of this microquasar is powered largely by its accretion disc rather than by the spin energy of the black hole.

Near-infrared jet emission in the microquasar XTE J1550-564

Context: Microquasars are accreting Galactic sources that are also observed to launch relativistic jets. A key signature of the ejection is non-thermal radio emission. The level of this jet component at high frequencies is still poorly constrained. Aims: The X-ray binary and microquasar black hole candidate XTE J1550-564 exhibited a faint X-ray outburst in April 2003 during which it stayed in the X-ray low/hard state. We took optical and near-infrared (NIR) observations with the ESO/NTT telescope during this outburst to disentangle the various contributions to the spectral energy distribution (SED) and investigate the presence of a jet component. Methods: Photometric and spectroscopic observations allowed us to construct an SED and also to produce a high time-resolution lightcurve. Results: The SED shows an abrupt change of slope from the NIR domain to the optical. The NIR emission is attributed to non-thermal synchrotron emission from the compact, self-absorbed jet that is known to be present in the low/hard state. This is corroborated by the fast variability, colours, lack of prominent spectral features and evidence for intrinsic polarisation. The SED suggests the jet break from the optically thick to the thin regime occurs in the NIR. Conclusions: The simultaneous optical-NIR data allow an independent confirmation of jet emission in the NIR. The transition to optically thin synchrotron occurs at NIR frequencies or below, which leads to an estimated characteristic size greater than 2x10^8cm and magnetic field less than 5T for the jet base, assuming a homogeneous one-zone synchrotron model.

AN IMPROVED DYNAMICAL MODEL FOR THE MICROQUASAR XTE J1550–564

We present an improved dynamical model of the X-ray binary and microquasar XTE J1550-564 based on new moderate-resolution optical spectroscopy and near-infrared photometry. By combining our new radial velocity measurements with previous measurements obtained 2001 May at the 8.2m VLT and with light curves, we find an orbital period of P=1.5420333 +/- 0.0000024 days and a radial velocity semiamplitude of K_2=363.14 +/- 5.97$ km/sec, which together imply an optical mass function of f(M)=7.65 +/- 0.38 solar masses. We find that the projected rotational velocity of the secondary star is 55 +/- 5 km/sec, which implies a very extreme mass ratio of Q=M/M_2=30. Using a model of a Roche lobe-filling star and an azimuthally symmetric accretion disk, we fit simultaneously optical light curves from 2001, near-infrared light curves from 2008 and all of the radial velocity measurements to derive system parameters. We find an inclination of 74.7 +/- 3.8 deg and component masses of M_2=0.30 +/- 0.07 solar masses and M=9.10 +/- 0.61 solar masses for the secondary star and black hole, respectively. The radius of the secondary star for the adopted model is 1.75 +/- 0.12 solar radii. Using this radius, the average K_S magnitude, and an extinction of A_K=0.507 +/- 0.050 mag, we find a distance of 4.38^{+0.58}_{-0.41} kpc, which is in good agreement with a recent distance estimate based on HI absorption lines (abstract shortened).

An unusual timing and spectral state of a black hole microquasar XTE J1550–564

An unusual timing and spectral state of a black hole microquasar XTE J1550–564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale in the light curves of black hole binaries, as suggested by Sunyaev & Revnivtsev (2000). The X-ray spectral fitting result indicates that there is an unusual soft component in the spectrum, which may be responsible for the millisecond variabilities. The millisecond variabilities as well as the unusual soft spectral component should be produced from some small, but independent active regions in the accretion disk.

X‐Ray Spectral Variability in the Initial Rise of XTE J1550−564

X-ray variability of the microquasar XTE J1550-564 is studied with time domain techniques for the data from the RXTE/PCA observation in September 8, 1998. The 2--60 keV averaged shot is obtained from superposing shots with one millisecond time bin through aligning their peaks. The spectral behavior during the averaged shot exhibits prominent differences from that observed in Cyg X-1. The hardness ratio of (13--60 keV)/(2--13 keV) or (16--60 keV)/(13--16 keV) during a shot is lower or higher than that of steady emission respectively. The correlation coefficient between intensity and hardness ratio of (13--60 keV)/(2--13 keV) or (16--60 keV)/(13--16 keV) is negative or positive respectively. These results may indicate that physical processes in the low state of XTE J1550-564 are different from those in Cyg X-1.

The Large-Scale, Decelerating X-ray Jets from the Microquasar Xte J1550−564: Evidence for External Shocks Caused by the Jet-Ism Interaction?

Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550—564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with the well-known Sedov evolutionary phase R ∝ t2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gammaray burst remnants, is shown to be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around the source is well below the canonical value nISM ∼ 1 cm−3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta.

An X‐Ray Timing Study of XTE J1550−564: Evolution of the Low‐Frequency Quasi‐periodic Oscillations for the Complete 2000 Outburst

We report on RXTE observations of the microquasar XTE J1550-564 during a ~70 day outburst in 2000 April-June. We focus here on the temporal properties of the source and study the behavior of low-frequency (0.1-10 Hz) quasi-periodic oscillations (LFQPOs), which seem to be of different types. We focus on the so-called type C (according to the classification of Remillard and collaborators), which corresponds to a strong 0.1-6 Hz LFQPO found to be present during at least 17 observations. We find that the frequency of the QPO is better correlated with the soft X-ray (≤7 keV) flux than with the hard flux (≥7 keV). If soft X-rays represent the behavior of an accretion disk, the relation shows that the disk may set the LFQPO frequency. In two cases, the identification of the type of QPO is not straightforward. If the QPOs in those two cases are type A (or B), then we may be seeing the QPO type alternate between type C and type A (or B), and this may represent some rapid changes in the physical properties of the accretion flow before the system stabilizes and slowly decays toward the end of the outburst. On the other hand, if all the QPOs are of type C, we may be observing an inversion in the frequency versus flux relation similar to that seen in GRO J1655-40. We discuss the QPO behavior in the framework of theoretical models.

Moving relativistic large-scale X-ray jets in the microquasar XTE J1550−564

We have discovered large-scale moving X-ray and radio jets from the microquasar XTE J1550−564. Using X-ray and radio observations performed between 2000 and 2002, we showed that plasma ejected from XTE J1550−564 has been able to travel at relativistic velocities during many years, with evidence for gradual deceleration. The broadband spectrum of the jets is consistent with synchrotron emission from high energy particles accelerated in shocks. Full details can be found in Corbel et al. [Science 298 (2002a) 196], Karret et al. [ApJ 582 (2003) 933] and Tomsick et al. [ApJ (2003) 945].

External Shock Model for the Large‐Scale, Relativistic X‐Ray Jets from the Microquasar XTE J1550−564

Large-scale, decelerating, relativistic X-ray jets due to material ejected from the black-hole candidate X-ray transient and microquasar XTE J1550-564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the eastern jet at the late time is consistent with the well-known Sedov evolutionary phase. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to be able to fit the observation data reasonably well. The inferred interstellar medium density around the source is well below the canonical value $n_ISM \sim 1 cm^{-3}$. We find that the emission from the continuously shocked interstellar medium (forward shock region) decays too slowly to be a viable mechanism for the eastern X-ray jet. However, the rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. To ensure the dominance of the emission from the shocked ejecta over that from the forward shock region during the period of the observations, the magnetic field and electron energy fractions in the forward shock region must be far below equipartition. Future continuous, follow-up multi-wavelength observations of new ejection events from microquasars up to the significant deceleration phase should provide more valuable insight into the nature of the interaction between the jets and external medium.

Spectral Evolution of the Microquasar XTE J1550−564 over Its Entire 2000 Outburst

We report on RXTE observations of the microquasar XTE J1550-564 during a ~70 day outburst in April-June 2000. We study the evolution of the PCA+HEXTE spectra over the outburst. The source transited from an initial Low Hard State (LS), to an Intermediate State (IS), and then back to the LS. The source shows an hysteresis effect similar to what is observed in other sources, favoring a common origin for the state transitions in soft X-ray transients. The first transition occurs at a ~ constant 2-200 keV flux, which probably indicates a change in the relative importance of the emitting media. The second transition is more likely driven by a drop in the mass accretion rate. In both LS, the spectra are characterized by the presence of a strong power-law tail (Compton corona) with a variable high energy cut-off. During the IS, the spectra show the presence of a ~0.8 keV thermal component (accretion disk). We discuss the apparently independent evolution of the two media, and show that right after the X-ray maximum on MJD 51662, the decrease of the source luminosity is due to a decrease of the power-law luminosity, at a constant disk luminosity. This, together with the detection of radio emission (with a spectrum typical of optically thin synchrotron emission), may suggest that the corona is ejected and further detected as a discrete radio ejection.

X‐Ray Emission from the Jets of XTE J1550−564

We report on X-ray observations of the large-scale jets recently discovered in the radio and detected in X-rays from the black hole candidate X-ray transient and microquasar XTE J1550-564. On 2002 March 11, X-ray emission was detected 23'' to the west of the black hole candidate and was extended along the jet axis with an FWHM of 12 and a full width at 10% of maximum intensity of 5''. The morphology of the X-ray emission matched well to that of the radio emission at the same epoch. The jet moved by 052 ± 013 between 2002 March 11 and June 19. The apparent speed during that interval was 5.2 ± 1.3 mas day-1. This is significantly less than the average apparent speed of 18.1 ± 0.4 mas day-1 from 1998 to 2002, assuming that the jet was ejected in 1998 September, and indicates that the jet has decelerated. The X-ray spectrum is adequately described by a power law with a photon index near 1.8 subject to interstellar absorption. The unabsorbed X-ray flux was 3.4 × 10-13 ergs cm-2 s-1 in the 0.3-8 keV band in 2002 March and decreased to 2.9 × 10-13 ergs cm-2 s-1 in June. We also detect X-rays from the eastern jet in 2002 March and show that it has decelerated and dimmed since the previous detections in 2000.

Large-scale, decelerating, relativistic x-ray jets from the microquasar XTE J1550-564.

We have detected, at x-ray and radio wavelengths, large-scale moving jets from the microquasar XTE J1550-564. Plasma ejected from near the black hole traveled at relativistic velocities for at least 4 years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high-energy (up to 10 tera-electron volts) particles that were accelerated in the shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-564 offers a rare opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei.

Chandra and RXTE spectroscopy of the Galactic microquasar XTE J1550-564 in outburst

On two occasions, we obtained nearly simultaneous ~ 4 kilosecond snapshot observations of the Galactic black hole and microquasar XTE J1550-564 with Chandra and RXTE near the peak of its May, 2000 outburst. The low-energy sensitivity of Chandra and the resolution of the High Energy Transmission Grating Spectrometer (HETGS), coupled with the broad energy range and large collecting area of RXTE, have allowed us to place constraints on the outburst accretion flow geometry of this source in the ``intermediate'' X-ray state. The 0.65-25.0 keV continuum spectra are well-described by relatively hot (kT ~ 0.8 keV) accretion disk and hard (Gamma ~ 2.3) coronal power-law components. Broad, relatively strong Fe K-alpha emission line (EW ~170 eV) and smeared absorption edge components consistent with Fe XXV are strongly required in joint spectral fits. The resolution of the Chandra/HETGS reveals that the broad Fe K-alpha emission lines seen clearly in the individual RXTE spectra are not due to an intrinsically narrow line.

High‐Frequency Quasi‐Periodic Oscillations in the 2000 Outburst of the Galactic Microquasar XTE J1550−564

We present an analysis of the high-frequency timing properties of the April-May 2000 outburst of the black hole candidate and Galactic microquasar XTE J1550-564, measured with the Rossi X-ray Timing Explorer, The rapid X-ray variability we measure is consistent with the source being in either the very high or intermediate canonical black hole state. A strong (5-8% RMS) quasi-periodic oscillation (QPO) is found between 249-278 Hz; this may represent the first recurrence of the same high-frequency QPO in subsequent outbursts of a transient black hole candidate. We also present possible evidence for a lower-frequency QPO at approximately 187 Hz, also reported previously and likely present simultaneously with the higher-frequency QPO. We discuss these findings within the context of the 1998 outburst of XTE J1550-564, and comment on implications for models of QPOs, accretion flows, and black hole spin.