We present the analysis of the X-ray variability and spectral timing properties of the ultraluminous X-ray source (ULX) NGC 5408 X-1, one of the most variable ULXs known so far. The variability ...properties are used as a diagnostic of the accretion state of the source and to derive estimates of the black hole (BH) mass. The observed high level of fast X-ray variability (fractional root-mean-square variability -- rms -- amplitude of ~30 per cent in the hard energy band), the hardening of the fractional rms spectrum and the properties of the quasi-periodic oscillation (QPO), all resemble those of a source in a hard-intermediate accretion state. We confirm the previous detection of a soft lag in the X-ray light curves of the source during 2006 and 2008 observations and find that the soft lag is still present in the more recent 2010/2011 observations. Using the entire available XMM-Newton data set (public as of 2012 February), we observe that the soft lag (of few seconds amplitude) is detected over a relatively large range of frequencies (ν ~ 5-90 mHz), which always includes the QPO frequencies. The soft lag displays energy-dependence, with the (absolute) amplitude increasing as a function of energy separation. We find close analogies with soft lags associated with type-C QPOs in BH binary systems (although an association to other types of QPOs cannot be completely excluded), as well as with reverberation lags observed in AGN. In both cases an intermediate-mass BH solution appears the most plausible. PUBLICATION ABSTRACT
Abstract
Black hole X-ray binaries undergo occasional outbursts caused by changing inner accretion flows. Here we report high angular resolution radio observations of the 2013 outburst of the black ...hole candidate X-ray binary system XTE J1908+094, using data from the Very Long Baseline Array and European VLBI Network. We show that following a hard-to-soft state transition, we detect moving jet knots that appear asymmetric in morphology and brightness, and expand to become laterally resolved as they move away from the core, along an axis aligned approximately −11° east of north. We initially see only the southern component, whose evolution gives rise to a 15-mJy radio flare and generates the observed radio polarization. This fades and becomes resolved out after 4 days, after which a second component appears to the north, moving in the opposite direction. From the timing of the appearance of the knots relative to the X-ray state transition, a 90° swing of the inferred magnetic field orientation, the asymmetric appearance of the knots, their complex and evolving morphology, and their low speeds, we interpret the knots as working surfaces where the jets impact the surrounding medium. This would imply a substantially denser environment surrounding XTE J1908+094 than has been inferred to exist around the microquasar sources GRS 1915+105 and GRO J1655−40.
ABSTRACT
We report the detection of an infrared burst lagging a thermonuclear Type I X-ray burst from the accreting neutron star (NS) 4U 1728-34 (GX 354-0). Observations were performed simultaneously ...with XMM–Newton (0.7–12 keV), NuSTAR (3–79 keV), and HAWK-I@VLT (2.2 $\, \mu$m). We measure a lag of 4.75 ± 0.5 s between the peaks of the emission in the two bands. Due to the length of the lag and the shape of the IR burst, we found that the most plausible cause for such a large delay is reprocessing of the Type I burst X-rays by the companion star. The inferred distance between the NS and the companion can be used to constrain the orbital period of the system, which we find to be larger than ∼66 min (or even ≳2 h, for a realistic inclination <75°). This is much larger than the current tentatively estimated period of ∼11 min. We discuss the physical implications on the nature of the binary and conclude that most likely the companion of 4U 1728-34 is a helium star.
MAXI J1836−194 is a Galactic black hole candidate X-ray binary that was discovered in 2011 when it went into outburst. In this paper, we present the full radio monitoring of this system during its ...‘failed’ outburst, in which the source did not complete a full set of state changes, only transitioning as far as the hard intermediate state. Observations with the Karl G. Jansky Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) show that the jet properties changed significantly during the outburst. The VLA observations detected linearly polarized emission at a level of ∼1 per cent early in the outburst, increasing to ∼3 per cent as the outburst peaked. High-resolution images with the Very Long Baseline Array (VLBA) show an ∼15 mas jet along the position angle −21 ± 2°, in agreement with the electric vector position angle found from our polarization results (−21 ± 4°), implying that the magnetic field is perpendicular to the jet. Astrometric observations suggest that the system required an asymmetric natal kick to explain its observed space velocity. Comparing quasi-simultaneous X-ray monitoring with the 5 GHz VLA observations from the 2011 outburst shows an unusually steep hard-state radio/X-ray correlation of
$L_{\rm R} \propto L_{\rm X}^{1.8\pm 0.2}$
, where L
R and L
X denote the radio and X-ray luminosities, respectively. With ATCA and Swift monitoring of the source during a period of re-brightening in 2012, we show that the system lay on the same steep correlation. Due to the low inclination of this system, we then investigate the possibility that the observed correlation may have been steepened by variable Doppler boosting.
We present a comprehensive spectral-timing study of the black hole candidate MAXI J1659−152 during its 2010 outburst. We analysed 65 Rossi X-ray timing explorer (RXTE) observations taken along this ...period, and computed the fundamental diagrams commonly used to study black hole transients. We fitted power density and energy spectra and studied the evolution of the spectral and timing parameters along the outburst. We discuss the evolution of the variability observed at different energy bands on the basis of the relative contribution of the disc and hard components to the energy spectrum of the source. We conclude that hard emission accounts for the observed fast variability, it being strongly quenched when type-B oscillations are observed. We find that both disc and hard emission are responsible for local count rate peaks until the system reaches the soft state. From that point, the peaks are only observed in the hard component, whereas the thermal component drops monotonically probably following the accretion rate decrease. We have also computed time-lags between soft and hard X-ray variability confirming that lags are larger during the hard-to-soft transition than during the hard state.
ABSTRACT
The X-ray light curves of accreting black holes and neutron stars in binary systems show various types of quasi-periodic oscillations (QPOs), the origin of which is still debated. The ...relativistic precession model identifies the QPO frequencies with fundamental time-scales from General Relativity, and has been proposed as a possible explanation of certain types of such oscillations. Under specific conditions (i.e. the detection of a particular QPOs triplet) such a model can be used to obtain self-consistent measurements of the mass and spin of the compact object. So far this has been possible only in the black hole binary GRO J1655-40. In the RXTE/PCA data from the 1999–2000 outburst of the black hole transient XTE J1859+226 we found a QPO triplet, and used the relativistic precession model to obtain high-precision measurements of the black hole mass and spin – M = (7.85 ± 0.46) M⊙, a* = 0.149 ± 0.005 – the former being consistent with the most recent dynamical mass determination from optical measurements. Similarly to what has been already observed in other black hole systems, the frequencies of the QPOs and broad-band noise components match the general relativistic frequencies of particle motion close to the compact object predicted by the model. Our findings confirm previous results and further support the validity of the relativistic precession model, which is the only electromagnetic-measurement-based method that so far has consistently yielded spins close to those from the gravitational waves produced by merging binary black holes.
Aims.
Flip-flops are top-hat-like X-ray flux variations, which have been observed in some transient accreting black hole binary systems, and feature simultaneous changes in the spectral hardness and ...the power density spectrum (PDS). They occur at a crucial time in the evolution of these systems, when the accretion disc emission starts to dominate over coronal emission. Flip-flops remain a poorly understood phenomenon, so we aim to thoroughly investigate them in a system featuring several such transitions.
Methods.
Within the multitude of observations of
Swift J1658.2-4242
during its outburst in early 2018, we detected 15 flip-flops, enabling a detailed analysis of their individual properties and the differences between them. We present observations by
XMM-Newton
,
NuSTAR
, Astrosat,
Swift
, Insight-HXMT, INTEGRAL, and ATCA. We analysed their light curves, searched for periodicities, computed their PDSs, and fitted their X-ray spectra, to investigate the source behaviour during flip-flop transitions and how the interval featuring flip-flops differs from the rest of the outburst.
Results.
The flip-flops of Swift J1658.2-4242 are of an extreme variety, exhibiting flux differences of up to 77% within ∼100 s, which is much larger than what has been seen previously. We observed radical changes in the PDS simultaneous with the sharp flux variations, featuring transitions between the quasi-periodic oscillation types C and A, which have never been observed before. Changes in the PDS are delayed, but more rapid than changes in the light curve. Flip-flops occur in two intervals within the outburst, separated by about two weeks in which these phenomena were not seen. Transitions between the two flip-flop states occurred at random integer multiples of a fundamental period of 2.761 ks in the first interval and 2.61 ks in the second. Spectral analysis reveals the high and low flux flip-flop states to be very similar, but distinct from intervals lacking flip-flops. A change of the inner temperature of the accretion disc is responsible for most of the flux difference in the flip-flops. We also highlight the importance of correcting for the influence of the dust scattering halo on the X-ray spectra.
ABSTRACT
We report on the first NuSTAR observation of the transitional millisecond pulsar binary XSS J12270–4859 during its current rotation-powered state, complemented with a 2.5 yr-long radio ...monitoring at Parkes telescope and archival XMM–Newton and Swift X-ray and optical data. The radio pulsar is mainly detected at 1.4 GHz displaying eclipses over $\sim 40{{\ \rm per\ cent}}$ of the 6.91 h orbital cycle. We derive a new updated radio ephemeris to study the 3–79 keV light curve that displays a significant orbital modulation with fractional amplitude of $28\pm 3{{\ \rm per\ cent}}$, a structured maximum centred at the inferior conjunction of the pulsar and no cycle-to-cycle or low–high-flaring mode variabilities. The average X-ray spectrum, extending up to ∼70 keV without a spectral break, is well described by a simple power law with photon index Γ = 1.17 ± 0.08 giving a 3–79 keV luminosity of $\rm 7.6_{-0.8}^{+3.8} \times 10^{32}\, erg\, s^{-1}$ for a distance of 1.37$_{-0.15}^{+0.69}$ kpc. Energy resolved orbital light curves reveal that the modulation is not energy dependent from 3 to 25 keV and is undetected with an upper limit of ${\sim} 10{{\ \rm per\ cent}}$ above 25 keV. Comparison with previous X-ray XMM–Newton observations in common energy ranges confirms that the modulation amplitudes vary on time-scales of a few months, indicative of a non-stationary contribution of the intrabinary shock (IBS) formed by the colliding winds of the pulsar and the companion. A more detailed inspection of energy resolved modulations than previously reported gives hints of a mild softening at superior conjunction of the pulsar below 3 keV, likely due to the contribution of the thermal emission from the neutron star. The IBS emission, if extending into the MeV range, would be energetically capable alone to irradiate the donor star.
A failed outburst of H1743−322 Capitanio, F.; Belloni, T.; Del Santo, M. ...
Monthly Notices of the Royal Astronomical Society,
09/2009, Letnik:
398, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We report on a campaign of X-ray and soft γ-ray observations of the black hole candidate (BHC) H1743−322 (also named IGR J17464-3213), performed with the RXTE, INTEGRAL and Swift satellites. The ...source was observed during a short outburst between 2008 October 03 and November 16. The evolution of the hardness–intensity diagram throughout the outburst is peculiar, in that it does not follow the canonical pattern through all the spectral states (the so-called q-track pattern) seen during the outburst of black hole transients. On the contrary, the source only makes a transition from the hard state to the hard–intermediate state. After this transition, the source decreases in luminosity and its spectrum hardens again. This behaviour is confirmed by both spectral and timing analyses. This kind of outburst has been rarely observed before in a transient BHC.
Abstract
We studied five XMM–Newton observations of the neutron star binary 4U 1728–34 covering the hard, intermediate and soft spectral states. By jointly fitting the spectra with several reflection ...models, we obtained an inclination angle of 25º–53º and an iron abundance up to 10 times the solar. From the fits with reflection models, we found that the fluxes of the reflection and the Comptonized components vary inconsistently; since the latter is assumed to be the illuminating source, this result possibly indicates the contribution of the neutron star surface/boundary layer to the disc reflection. As the source evolved from the relatively soft to the intermediate state, the disc inner radius decreased, opposite to the prediction of the standard accretion disc model. We also explore the possible reasons why the supersolar iron abundance is required by the data and found that this high value is probably caused by the absence of the hard photons in the XMM–Newton data.
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