T. Belloni

Hard X‐ray states and radio emission in GRS 1915+105

We compare simultaneous Ryle Telescope radio and Rossi X-Ray Timing Explorer X-ray observations of the galactic microquasar GRS 1915+105, using the classification of the X-ray behaviour in terms of three states as previously established. We find a strong (one-to-one) relation between radio oscillation events and series of spectrally hard states in the X-ray light curves, if the hard states are longer than ∼100 s and are well separated from each other. In all other cases the source shows either low-level or high-level radio emission, but no radio oscillation events. During intervals when the source stays in the hard spectral state for periods of days to months, the radio behaviour is quite different; during some of these intervals a quasi-continuous jet is formed with an almost flat synchrotron spectrum extending to at least the near-infrared. Based on the similarities between the oscillation profiles at different wavelengths, we suggest a scenario which can explain most of the complex X-ray:radio behaviour of GRS 1915+105. We compare this behaviour with that of other black hole sources, and challenge previous reports of a relation between spectrally soft X-ray states and the radio emission.

A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U 1728-34

We present the results of a multi-Lorentzian fit to the power spectra of two kilohertz quasi-periodic oscillation (QPO) sources: 4U 0614+09 and 4U 1728-34. This work was triggered by recent results of a similar fit to the black hole candidates (BHCs) GX 339-4 and Cyg X-1 by Nowak in 2000. We find that one to six Lorentzians are needed to fit the power spectra of our two sources. The use of exactly the same fit function reveals that the timing behavior of 4U 0614+09 and 4U 1728-34 is almost identical at luminosities that are about a factor of 5 different. As the characteristic frequency of the Lorentzians we use the frequency νmax, at which each component contributes most of its variance per log frequency, as proposed by Belloni, Psaltis, & van der Klis in 2001. When using νmax instead of the centroid frequency of the Lorentzian, the recently discovered hectohertz Lorentzian is practically constant in frequency. We use our results to test the suggestions by Psaltis, Belloni, & van der Klis in 1999 and Nowak in 2000 that the two Lorentzians describing the high-frequency end of the broadband noise in BHCs in the low state can be identified with the kilohertz QPOs in the neutron star low-mass X-ray binaries. The prediction for the neutron star sources is that if the two kilohertz QPOs are present, then these two high-frequency Lorentzians should be absent from the broadband noise. We find that when the two kilohertz QPOs are clearly present, the low-frequency part of the power spectrum is too complicated to draw immediate conclusions from the nature of the components detected in any one power spectrum. However, the relations we observe between the characteristic frequencies of the kilohertz QPOs and the band-limited noise, when compared to the corresponding relations in BHCs, hint toward the identification of the second highest frequency Lorentzian in the BHCs with the lower kilohertz QPO. They do not confirm the identification of the highest frequency Lorentzian with the upper kilohertz QPO.

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 2000 April-May 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 black hole state. Strong (5%-8% rms) quasi-periodic oscillations (QPOs) are found between 249 and 276 Hz; this represents the first detection of the same high-frequency QPO in subsequent outbursts of a transient black hole candidate. We also present evidence for lower frequency QPOs at approximately 188 Hz (3.5 σ, single trial), also reported previously and likely present simultaneously with the higher frequency QPOs. 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.

Chandra Observations of the Anomalous X-ray Pulsar 4U 0142+61

We present X-ray imaging, timing, and phase-resolved spectroscopy of the anomalous X-ray pulsar 4U 0142+61 using the Chandra X-Ray Observatory. The spectrum is well described by a power-law plus blackbody model with Γ = 3.35(2), kTBB = 0.458(3) keV, and NH = 0.91(2) × 1022 cm-2; we find no significant evidence for spectral features (0.5-7.0 keV). Time-resolved X-ray spectroscopy shows evidence for evolution in phase in either Γ, kTBB, or some combination thereof as a function of pulse phase. We derive a precise X-ray position for the source and determine its spin period, P = 8.68866(30) s. We have detected emission beyond 4 from the central source and extending beyond 100, likely due to dust scattering in the interstellar medium.

Spectral evolution of the Atoll source 4U 1728-34 with RXTE and INTEGRAL: evidence for hard X-ray tail

We report the temporal and spectral results on the INTEGRAL and RXTE 2006–2007 observation campaign of the Atoll source 4U 1728–34 (GX 354‐0). The source shows, more than once, spectral evolution as revealed by the hardness intensity diagram. The soft state is well described by a Comptonization with an electron temperature of 3 keV and a high optical depth of 6. In the hard spectral state the emission extends to above 100 keV and it can be described by Comptoniziation (with higher temperature of 10 keV) plus a power law component with Γ of 1.8, which is evidence for non‐thermal emission from the source.

The X-ray emission of the intermediate polar V709 Cas

We present RXTE and BeppoSAX observations of the Intermediate Polar V 709 Cas acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30 keV is dominated by the strong pulsation at the rotational period of the white dwarf (312.8 s) with no sign of orbital or sideband periodicity, thus conrming previous ROSAT results. However, we detect changes in the power spectra between the two epochs. While the second harmonic of the spin period is present during both observations, the rst harmonic is absent in 1997. An increase in the amplitude of the spin pulsation is found between 1997 and 1998 together with a decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100 keV is well described by an isothermal plasma at 27 keV plus complex absorption and an iron K fluorescent line, due to reflection from the white dwarf surface. The rotational pulsation is compatible with complex absorption dominating the low energy range, while the high energy spin modulation can be attributed to tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the presence of an absorption edge from ionized iron likely located in the pre{shock accretion flow. The variations along the spin period of the partial covering absorber and of reflection are compatible with the classical accretion curtain scenario. The variations in the spin pulse characteristics and X-ray flux indicate that V 709 Cas experiences changes in the mass accretion rate on timescales from months to years.

A late jet rebrightening revealed from multiwavelength monitoring of the black hole candidate XTE J1752−223

We present optical monitoring of the black hole candidate XTE J1752−223 during its 2009–10 outburst and decay to quiescence. The optical light curve can be described by an exponential decay followed by a plateau, then a more rapid fade towards quiescence. The plateau appears to be due to an extra component of optical emission that brightens and then fades over ∼40 days. We show evidence for the origin of this optical ‘flare’ to be the synchrotron jet during the decaying hard state, and we identify and isolate both disc and jet components in the spectral energy distributions. The optical flare has the same morphology and amplitude as a contemporaneous X-ray rebrightening. This suggests a common origin, but no firm conclusions can be made favouring or disfavouring the jet producing the X-ray flare. The quiescent optical magnitudes are B ≥ 20.6,V ≥ 21.1,R ≥ 19.5,i � ≥ 19.2. From the optical outburst amplitude we estimate a likely orbital period of <22 h. We also present near-infrared (NIR) photometry and polarimetry and rare mid-IR imaging (8–12 µm) when the source is nearing quiescence. The fading jet component, and possibly the companion star, may contribute to the NIR flux. We derive deep mid-IR flux upper limits and NIR linear polarization upper limits. With the inclusion of radio data, we measure an almost flat jet spectral index between radio and optical; Fν ∝ ν ∼+0.05 . The data favour the jet break to optically thin emission to

Broad iron line in the fast spinning neutron-star system 4U 1636-53

We analysed the X-ray spectra of six observations, simultaneously taken with XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the neutron-star low-mass X-ray binary 4U 1636-53. The observations cover several states of the source, and therefore a large range of inferred mass accretion rate. These six observations show a broad emission line in the spectrum at around 6.5 keV, likely due to iron. We fitted this line with a set of phenomenological models of a relativistically broadened line, plus a model that accounts for relativistically smeared and ionized reflection from the accretion disc. The latter model includes the incident emission from both the neutron-star surface or boundary layer and the corona that is responsible for the high-energy emission in these systems. From the fits with the reflection model we found that in four out of the six observations the main contribution to the reflected spectrum comes from the neutron-star surface or boundary layer, whereas in the other two observations the main contribution to the reflected spectrum comes from the corona. We found that the relative contribution of these two components is not correlated to the state of the source. From the phenomenological models, we found that the iron line profile is better described by a symmetric, albeit broad, profile. The width of the line cannot be explained only by Compton broadening, and we therefore explored the case of relativistic broadening. We further found that the direct emission from the disc, boundary layer and corona generally evolved in a manner consistent with the standard accretion disc model, with the disc and boundary layer becoming hotter and the disc moving inwards as the source changed from the hard to the soft state. The iron line, however, did not appear to follow the same trend.

X-ray spectrum and variability of the black hole candidate LMC X-3

LMC X-3 was observed on seven occasions in 1983-1984 with the Exosat satellite covering various orbital phases. No phase related variability was detected, while the X-ray flux increased gradually by about 30 percent in two weeks. Analysis of the short term variability in terms of autocorrelation reveals a minimum time scale of 600 s, with an rms amplitude of about 1 percent. Energy spectra in the 0.3-9 keV range have been fitted with various analytical laws. A good fit is obtained with the Comptonization spectrum given by Sunyaev and Titarchuk (1980), yielding an optical depth tau about 23 and a temperature of about 1 keV. The results are compared with those of Cygnus X-1 in the low state and with the expectations of the standard accretion disk model. 44 references.

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

On two occasions, we obtained nearly simultaneous ≃4 ks snapshot observations of the Galactic black hole and microquasar XTE J1550-564 with Chandra and RXTE near the peak of its 2000 May 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 a relatively hot (kT ≃ 0.8 keV) accretion disc and hard (Γ ≃ 2.3) coronal power-law components. Broad, relatively strong Fe Ka emission line (W K α ≃ 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 Kα emission lines seen clearly in the individual RXTE spectra are not the result of an intrinsically narrow line.