arXiv subjects

R. P. Fender

Publications and source records attributed to R. P. Fender.

At least 145 records · Page 8Linked to original sources

arXiv2010

Powerful jets from accreting black holes: evidence from the optical and infrared

A common consequence of accretion onto black holes is the formation of powerful, relativistic jets that escape the system. In the case of supermassive black holes at the centres of galaxies this has been known for decades, but for stellar-mass black holes residing within galaxies like our own, it has taken recent advances to arrive at this conclusion. Here, a review is given of the evidence that supports the existence of jets from accreting stellar-mass black holes, from observations made at optical and infrared wavelengths. In particular it is found that on occasion, jets can dominate the emission of these systems at these wavelengths. In addition, the interactions between the jets and the surrounding matter produce optical and infrared emission on large scales via thermal and non-thermal processes. The evidence, implications and applications in the context of jet physics are discussed. It is shown that many properties of the jets can be constrained from these studies, including the total kinetic power they contain. The main conclusion is that like the supermassive black holes, the jet kinetic power of accreting stellar-mass black holes is sometimes comparable to their bolometric radiative luminosity. Future studies can test ubiquities in jet properties between objects, and attempt to unify the properties of jets from all observable accreting black holes, i.e. of all masses.

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arXiv2009

The complete spectrum of the neutron star X-ray binary 4U0614+091

We observed the neutron star (NS) ultra-compact X-ray binary 4U0614+091 quasi-simultaneously in the radio band (VLA), mid-IR/IR (Spitzer/MIPS and IRAC), near-IR/optical (SMARTS), optical-UV (Swift/UVOT), soft and hard X-rays (Swift/XRT and RXTE). The source was steadily in its `hard state'. We detected the source in the whole range, for the first time in the radio band at 4.86 and 8.46 GHz and in the mid-IR at 24 um, up to 100 keV. The optically thick synchrotron spectrum of the jet is consistent with being flat from the radio to the mid-IR band. The flat jet spectrum breaks in the range (1-4)x10^(13) Hz to an optically-thin power-law synchrotron spectrum with spectral index ~-0.5. These observations allow us to estimate a lower limit on the jet radiative power of ~3x10^(32) erg/s and a total jet power Lj~10^(34) u_(0.05)^(-1) Ec^(0.53) erg/s (where Ec is the high-energy cutoff of the synchrotron spectrum in eV and u_(0.05) is the radiative efficiency in units of 0.05). The contemporaneous detection of the optically thin part of the compact jet and the X-ray tail above 30 keV allows us to assess the contribution of the jet to the hard X-ray tail by synchrotron self-Compton (SSC) processes. We conclude that, for realistic jet size, boosting, viewing angle and energy partition, the SSC emission alone, from the post-shock, accelerated, non-thermal population in the jet, is not a viable mechanism to explain the observed hard X-ray tail of the neutron star 4U0614+091.

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arXiv2009

A long-term optical - X-ray correlation in 4U 1957+11

[abridged] Three years of optical monitoring of the low-mass X-ray binary (LMXB) 4U 1957+11 is presented. The source was observed in V, R and i-bands using the Faulkes Telescopes North and South. The light curve is dominated by long-term variations which are correlated (at the > 3 sigma level) with the RXTE ASM soft X-ray flux. The variations span one magnitude in all three filters. We find no evidence for periodicities in our light curves, contrary to a previous short-timescale optical study in which the flux varied on a 9.3-hour sinusoidal period by a smaller amplitude. The optical spectral energy distribution is blue and typical of LMXBs in outburst, as is the power law index of the correlation beta = 0.5, where F_{nu,OPT} propto F_X^beta. The discrete cross-correlation function reveals a peak at an X-ray lag of 2 - 14 days, which could be the viscous timescale. However, adopting the least squares method the strongest correlation is at a lag of 0 +/- 4 days, consistent with X-ray reprocessing on the surface of the disc. We therefore constrain the optical lag behind X-ray to be between -14 and +4 days. In addition, we use the optical - X-ray luminosity diagram for LMXBs as a diagnostic tool to constrain the nature of the compact object in 4U 1957+11, since black hole (BH) and neutron star (NS) sources reside in different regions of this diagram. If the system contains a BH (as is the currently favoured hypothesis), its distance must exceed ~ 20 kpc for the optical and X-ray luminosities to be consistent with other soft state BH systems. For distances < 20 kpc, the data lie in a region of the diagram populated only by NS sources. 4U 1957+11 is unique: it is either the only BH LMXB to exist in an apparent persistent soft state, or it is a NS LMXB which behaves like a black hole.

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arXiv2009

Probing the behaviour of the X-ray binary Cygnus X-3 with very-long-baseline radio interferometry

In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cyg X-3, we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival VLBA data at 5 or 15 GHz and new e-EVN data at 5 GHz. We also present 5 GHz MERLIN observations of an outburst of Cyg X-3. In the X-ray regime we use quasi-simultaneous with radio, monitoring and pointed RXTE observations. We find that when the radio emission from both jet and core is globally considered, the behaviour of Cyg X-3 at milliarcsecond scales is consistent with that described at arcsecond scales. However, when the radio emission is disentangled in a core component and a jet component the situation changes. It becomes clear that in active states the radio emission from the jet is dominating that from the core. This shows that in these states the overall radio flux cannot be used as a direct tracer of the accretion state.

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arXiv2009

The proper motion and changing jet morphology of Cygnus X-3

We present analysis of 25 years' worth of archival VLA, VLBA and EVN observations of the X-ray binary Cygnus X-3. From this, we deduce the source proper motion, allowing us to predict the location of the central binary system at any given time. However, the line of sight is too scatter-broadened for us to measure a parallactic distance to the source. The measured proper motion allows us to constrain the three-dimensional space velocity of the system, implying a minimum peculiar velocity of 9 km/s. Reinterpreting VLBI images from the literature using accurate core positions shows the jet orientation to vary with time, implying that the jets are oriented close to the line of sight and are likely to be precessing.

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arXiv2009

'Disc-jet' coupling in black hole X-ray binaries and active galactic nuclei

In this chapter I will review the status of our phenomenological understanding of the relation between accretion and outflows in accreting black hole systems. This understanding arises primarily from observing the relation between X-ray and longer wavelength (infrared, radio) emission. The view is necessarily a biased one, beginning with observations of X-ray binary systems, and attempting to see if they match with the general observational properties of active galactic nuclei.

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arXiv2009

Following the 2008 outburst decay of the black hole candidate H1743-322 in X-ray and radio

In this Paper we report on radio (VLA and ATCA) and X-ray (RXTE, Chandra and Swift) observations of the outburst decay of the transient black hole candidate H1743-322 in early 2008. We find that the X-ray light curve followed an exponential decay, leveling off towards its quiescent level. The exponential decay timescale is ~4 days and the quiescent flux corresponds to a luminosity of 3x10^32 (d/7.5 kpc)^2 erg/s. This together with the relation between quiescent X-ray luminosity and orbital period reported in the literature suggests that H1743-322 has an orbital period longer than ~10 hours. Both the radio and X-ray light curve show evidence for flares. The radio - X-ray correlation can be well described by a power-law with index ~0.18. This is much lower than the index of 0.6-0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low-hard state, is -0.5+-0.15, which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low-hard state. We attribute the radio flares and the low index for the radio - X-ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X-ray power law spectral index during the decay, although the relatively high extinction of N_H =2.3x10^22 cm^-2 limits the detected number of soft photons and thus the accuracy of the spectral fits.

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arXiv2009

The disc-jet coupling in the neutron star X-ray binary Aquila X-1

We study the accretion/ejection processes (i.e. disc/jet coupling) in the neutron star X-ray binary Aquila X-1 via a multi-wavelength approach. We use in the radio band the publicly available VLA archive containing observations of the object between 1986-2005, in the X-ray band the archival RXTE data (PCA and HEXTE) between 1997-2008, and in optical (R band) observations with the SMARTS recorded between 1998-2007. In the combined data set we find three outbursts for which quasi-simultaneous radio, optical (R band) and X-ray data exist and focus on them to some extent. We provide evidence that the disc/jet coupling in Aquila X-1 is similar to what has been observed in black hole X-ray binaries, at least from the point of view of the behaviour in the hardness-intensity diagrams (the hysteresis effect included), when the phenomenology of the jet is taken into account. Although based on a very small number of observations, a radio/X-ray correlation seems to exist for this system, with a slope of alpha=0.40 +/- 0.07 (F_{radio} \propto F_{X}^{alpha}), which is different than the slope of alpha=1.40 +/- 0.25 found for another atoll source, 4U 1728-34, but interestingly enough is relatively close to the values obtained for several black hole X-ray binaries. No significant correlation is found between the radio and optical (R band) emissions. We also report a significant drop in the radio flux from Aql X-1 above an X-ray flux of ~ 5 X 10^{-9} erg cm^{-2} s^{-1}. This behaviour, also reported in the neutron star X-ray binary 4U 1728-34, may be analogous to the suppression of radio emission in black hole X-ray binaries in bright, soft X-ray states. It suggests that from this point of view neutron star X-ray binaries can mimic the behaviour of black hole X-ray binaries in suppressing the jet in soft/disc-dominated X-ray states.

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arXiv2009

The Quiescent Spectral Energy Distribution of V404 Cyg

We present a multiwavelength study of the black hole X-ray binary V404 Cyg in quiescence, focusing upon the spectral energy distribution (SED). Radio, optical, UV, and X-ray coverage is simultaneous. We supplement the SED with additional non-simultaneous data in the optical through infrared where necessary. The compiled SED is the most complete available for this, the X-ray and radio brightest quiescent black hole system. We find no need for a substantial contribution from accretion light from the near-UV to the near-IR, and in particular the weak UV emission constrains published spectral models for V404 Cyg. We confirm that no plausible companion spectrum and interstellar extinction can fully explain the mid-IR, however, and an IR excess from a jet or cool disc appears to be required. The X-ray spectrum is consistent with a Gamma~2 power-law as found by all other studies to date. There is no evidence for any variation in the hardness over a range of a factor of 10 in luminosity. The radio flux is consistent with a flat spectrum (in f(nu)). The break frequency between a flat and optically thin spectrum most likely occurs in the mid or far-IR, but is not strongly constrained by these data. We find the radio to be substantially variable but with no clear correlation with X-ray variability.

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arXiv2009

A new perspective on GCRT J1745-3009

Two WSRT observations were performed and five archival VLA data were reduced in order to redetect the enigmatic radio transient GCRT J1745-3009. The source was not redetected. We were, however, able to extract important new information from the discovery dataset. Our reanalysis excludes models that predict symmetric bursts, but the transient white dwarf pulsar is favoured. Although we now have more contraints on the properties of this source, we are still unsure about its basic model.

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arXiv2009

On the variation of black hole accretion disc radii as a function of state and accretion rate

Black hole binary transients undergo dramatic evolution in their X-ray timing and spectral behaviour during outbursts. In recent years a paradigm has arisen in which "soft" X-ray states are associated with an inner disc radius at, or very close to, the innermost stable circular orbit (ISCO) around the black hole, while in "hard" X-ray states the inner edge of the disc is further from the black hole. Models of advective flows suggest that as the X-ray luminosity drops in hard states, the inner disc progressively recedes, from a few to hundreds gravitational radii. Recent observations which show broad iron line detections and estimates of the disc component strength suggest that a non-recessed disc could still be present in bright hard states. In this study we present a comprehensive analysis of the spectral components associated with the inner disc, utilising data from instruments with sensitive low-energy responses and including reanalyses of previously published results. A key component of the study is to fully estimate systematic uncertainties by e.g. investigating in detail the effect of having a hydrogen column density that is fixed or free to vary. We conclude that for L_x > 0.01 of the Eddington limit, spectral fits allow us to constrain the disc to be < 10R_g. There is, however, clear evidence that when L_x is between 10^-2-- 10^-3 Eddington, the disc does begin to recede. We include measurements of disc radii in two quiescent black hole binaries, and present the inferred evolution of accretion parameters in the entire range of bolometric luminosities 10^-8 -- 1 Eddington. We compare our results with theoretical models and note that the implied rate of disc recession with luminosity is consistent with recent empirical results on the X-ray timing behaviour of black holes of all masses.

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arXiv2009

Jets from black hole X-ray binaries: testing, refining and extending empirical models for the coupling to X-rays

In this paper we study the relation of radio emission to X-ray spectral and variability properties for a large sample of black hole X-ray binary systems. This is done to test, refine and extend -- notably into the timing properties -- the previously published `unified model' for the coupling of accretion and ejection in such sources. In 14 outbursts from 11 different sources we find that in every case the peak radio flux, on occasion directly resolved into discrete relativistic ejections, is associated with the bright hard to soft state transition near the peak of the outburst. We also note the association of the radio flaring with periods of X-ray flaring during this transition in most, but not all, of the systems. In the soft state, radio emission is in nearly all cases either undetectable or optically thin, consistent with the suppression of the core jet in these states and `relic' radio emission from interactions of previously ejected material and the ambient medium. However, these data cannot rule out an intermittent, optically thin, jet in the soft state. In attempting to associate X-ray timing properties with the ejection events we find a close, but not exact, correspondence between phases of very low integrated X-ray variability and such ejections. In summary we find no strong evidence against the originally proposed model, confirming and extending some aspects of it with a much larger sample, but note that several aspects remain poorly tested. (ABRIDGED)

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arXiv2008

An anti-correlation between X-ray luminosity and H-alpha equivalent width in X-ray binaries

We report an anticorrelation between continuum luminosity and the equivalent width (EW) of the H-alpha emission line in X-ray binary systems. The effect is evident both in a universal monotonic increase in H-alpha EW with time following outbursts, as systems fade, and in a comparison between measured EWs and contemporaneous X-ray measurements. The effect is most clear for black hole binaries in the low/hard X-ray state, which is prevalent at X-ray luminosities below ~1% Eddington. We do not find strong evidence for significant changes in line profiles across accretion state changes, but this is hampered by a lack of good data at such times. The observed anti-correlation, highly significant for black hole binaries, is only marginally so for neutron star systems, for which there are far less data. Comparison with previously established correlations between optical and X-ray luminosity suggest that the line luminosity is falling as the X-ray and optical luminosities drop, but not as fast (approximately as L_{H-alpha} \propto L_X^{~0.4} \propto L_{opt}^{~0.7}). We briefly discuss possible origins for such an effect, including the optical depth, form of the irradiating spectrum and geometry of the accetion flow. Further refinement of the relation in the future may allow measurements of H-alpha EW to be used to estimate the luminosity of, and hence the distance to, X-ray binary systems. Beyond this, further progress will require a better sample of spectro-photometric data.

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arXiv2008

Broad-band X-ray spectral evolution of GX 339-4 during a state transition

We report on X-ray and soft gamma-ray observations of the black-hole candidate GX 339-4 during its 2007 outburst, performed with the RXTE and INTEGRAL satellites. The hardness-intensity diagram of all RXTE/PCA data combined shows a q-shaped track similar to that observed in previous outbursts.The evolution in the diagram suggested that a transition from hard-intermediate state to soft-intermediate state occurred, simultaneously with INTEGRAL observations performed in March. The transition is confirmed by the timing analysis presented in this work, which reveals that a weak type-A quasi-periodic oscillation (QPO) replaces a strong type-C QPO. At the same time, spectral analysis shows that the flux of the high-energy component shows a significant decrease in its flux. However, we observe a delay (roughly one day) between variations of the spectral parameters of the high-energy component and changes in the flux and timing properties. The changes in the high-energy component can be explained either in terms the high-energy cut-off or in terms of a variations in the reflection component. We compare our results with those from a similar transition during the 2004 outburst of GX 339-4.

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arXiv2008

Blazing trails: Microquasars as head-tail sources and the seeding of magnetized plasma into the ISM

We discuss the dynamics of microquasar jets in the interstellar medium, with specific focus on the effects of the X-ray binaries' space velocity with respect to the local Galactic standard of rest. We argue that, during late stages in the evolution of large scale radio nebulae around microquasars, the ram pressure of the interstellar medium due to the microquasar's space velocity becomes important and that microquasars with high velocities form the Galactic equivalent of extragalactic head-tail sources, i.e., that they leave behind trails of stripped radio plasma. Because of their higher space velocities, low-mass X-ray binaries are more likely to leave trails than high-mass X-ray binaries. We show that the volume of radio plasma released by microquasars over the history of the Galaxy is comparable to the disk volume and argue that a fraction of a few percent of the radio plasma left behind by the X-ray binary is likely mixed with the neutral phases of the ISM before the plasma is removed from the disk by buoyancy. Because the formation of microquasars is an unavoidable by-product of star formation, and because they can travel far from their birth places, their activity likely has important consequences for the evolution of magnetic fields in forming galaxies. We show that radio emission from the plasma inside the trail should be detectable at low frequencies. We suggest that LMXBs with high detected proper motions like XTE J1118+480 will be the best candidates for such a search.

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arXiv2008

A decade of radio imaging the relativistic outflow in the peculiar X-ray binary Circinus X-1

We present observations of the neutron star X-ray binary and relativistic jet source Circinus X-1 made at 4.8 and 8.6 GHz with the Australia Telescope Compact Array during a time interval of almost 10 years. The system shows significant variations in the morphology and brightness of the radio features on all timescales from days to years. Using the time delay between the successive brightening of the different components of the radio emission we were able to provide further evidence for the relativistic nature of the arcsec scale outflow, with an apparent velocity beta_app >= 12. No compelling evidence for an evolution of the orientation of the jet axis was found. We also place an upper limit on the proper motion of the system which is consistent with previous optical studies. Besides the previously reported radio flares close to the orbital phase 0.0 (interpreted as enhanced accretion at periastron passage), we also identified outbursts with similar properties near the orbital phase 0.5. The global spectral index revealed a preferentially steep spectrum over the entire period of monitoring with a mean value and standard deviation alpha=-0.9 +/- 0.6 (F_nu ~ nu^{alpha}), which became significantly flatter during the outbursts. Polarization was detected in one third of the epochs and in one case Faraday rotation close to the core of the system was measured.

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arXiv2008

Zooming in on a sleeping giant: milliarcsecond HSA imaging of the black hole binary V404 Cyg in quiescence

Observations of the black hole X-ray binary V404 Cyg with the very long baseline interferometer HSA (the High Sensitivity Array) have detected the source at a frequency of 8.4 GHz, providing a source position accurate to 0.3 mas relative to the calibrator source. The observations put an upper limit of 1.3 mas on the source size (5.2 AU at 4 kpc) and a lower limit of 7 x 10^6 K on its brightness temperature during the normal quiescent state, implying that the radio emission must be non-thermal, most probably synchrotron radiation, possibly from a jet. The radio lightcurves show a short flare, with a rise time of about 30 min, confirming that the source remains active in the quiescent state.

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arXiv2008

Coupled radio and X-ray emission and evidence for discrete ejecta in the jets of SS 433

We present five epochs of simultaneous radio (VLA) and X-ray (Chandra) observations of SS 433, to study the relation between the radio and X-ray emission in the arcsecond-scale jets of the source. We detected X-ray emission from the extended jets in only one of the five epochs of observation, indicating that the X-ray reheating mechanism is transient. The reheating does not correlate with the total flux in the core or in the extended radio jets. However, the radio emission in the X-ray reheating regions is enhanced when X-ray emission is present. Deep images of the jets in linear polarization show that outside of the core, the magnetic field in the jets is aligned parallel to the local velocity vector, strengthening the case for the jets to be composed of discrete bullets rather than being continuous flux tubes. We also observed anomalous regions of polarized emission well away from the kinematic trace, confirming the large-scale anisotropy of the magnetic field in the ambient medium surrounding the jets.

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