Energetics of jets from X-ray binaries

I discuss the energetics of synchrotron-emitting outflows, increasingly found to be present in many different classes of X-ray binary systems. It is shown that the outflow is likely to be comparable in power to the integrated X-ray luminosity, traditionally taken to be an indicator of the global mass-transfer rate. This is especially found to be the case in the (low/)hard states of black hole candidate systems. I conclude that jets are extremely important, energetically and dynamically, for the accretion process in the majority of known X-ray binary systems.Comment: To be published in `Proceedings of the Third Microquasar Workshop: Granada Workshop on galactic relativistic jet sources', Eds A. J. Castro-Tirado, J. Greiner and J. M. Paredes, Astrophysics and Space Science, in pres

Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks

We present 5-GHz MERLIN radio images of the microquasar GRS 1915+105 during two separate outbursts in 2001 March and 2001 July, following the evolution of the jet components as they move outwards from the core of the system. Proper motions constrain the intrinsic jet speed to be >0.57c, but the uncertainty in the source distance prevents an accurate determination of the jet speed. No deceleration is observed in the jet components out to an angular separation of about 300mas. Linear polarisation is observed in the approaching jet component, with a gradual rotation in position angle and a decreasing fractional polarisation with time. Our data lend support to the internal shock model whereby the jet velocity increases leading to internal shocks in the pre-existing outflow before the jet switches off. The compact nuclear jet is seen to re-establish itself within two days, and is visible as core emission at all epochs. The energetics of the source are calculated for the possible range of distances; a minimum power of 1-10 per cent of the Eddington luminosity is required to launch the jet.Comment: 18 pages, 14 figures, accepted for publication in MNRAS. For higher-resolution versions of Figures 3, 5, and 12, see http://remote.science.uva.nl/~jmiller/grs1915/figures.htm

A highly polarised radio jet during the 1998 outburst of the black hole transient XTE J1748-288

XTE J1748-288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray lightcurves showed canonical morphologies, with minor variations on the ``Fast Rise Exponential Decay'' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional (>20%) fractional linear polarisation, the variability of which was anti-correlated with the flux density. We use this variability to discuss possible depolarisation mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components.Comment: Accepted for publication in MNRA

The radio luminosity of persistent X-ray binaries

We summarise all the reported detections of, and upper limits to, the radio emission from persistent (i.e. non-transient) X-ray binaries. A striking result is a common mean observed radio luminosity from the black hole candidates (BHCs) in the Low/Hard X-ray state and the neutron-star Z sources on the horizontal X-ray branch. This implies a common mean intrinsic radio luminosity to within a factor of twenty five (or less, if there is significant Doppler boosting of the radio emission). Unless coincidental, these results imply a physical mechanism for jet formation which requires neither a black hole event horizon or a neutron star surface. As a whole the populations of Atoll and X-ray pulsar systems are less luminous by factors of >5 and >10 at radio wavelengths than the BHCs and Z sources (while some Atoll sources have been detected, no high-field X-ray pulsar has ever been reliably detected as a radio source). We suggest that all of the persistent BHCs and the Z sources generate, at least sporadically, an outflow with physical dimensions > 1e12cm, i.e. significantly larger than the binary separations of most of the systems. We compare the physical conditions of accretion in each of the types of persistent X-ray binary and conclude that a relatively low (<1e10 G) magnetic field associated with the accreting object, and a high (>0.1 Eddington) accretion rate and/or dramatic physical change in the accretion flow, are required for formation of a radio-emitting outflow or jet.Comment: Accepted for publication in MNRA

Steady jets from radiatively efficient hard states in GRS 1915+105

Recent studies of different X-ray binaries (XRBs) have shown a clear correlation between the radio and X-ray emission. We present evidence of a close relationship found between the radio and X-ray emission at different epochs for GRS1915+105, using observations from the Ryle Telescope and Rossi X-ray Timing Explorer satellite. The strongest correlation was found during the hard state (also known as the `plateau' state), where a steady AU-scale jet is known to exist. Both the radio and X-ray emission were found to decay from the start of most plateau states, with the radio emission decaying faster. An empirical relationship of $S_{\rm{radio}}\propto S_{\rm{X-ray}}^{\xi}$ was then fitted to data taken only during the plateau state, resulting in a power-law index of $\xi\sim1.7\pm0.3$, which is significantly higher than in other black hole XRBs in a similar state. An advection-flow model was then fitted to this relationship and compared to the universal XRB relationship as described by Gallo et al. (2003). We conclude that either (I) the accretion disk in this source is radiatively efficient, even during the continuous outflow of a compact jet, which could also suggest a universal turn-over from radiatively inefficient to efficient for all stellar-mass black holes at a critical mass accretion rate ($\dot{m}_{\rm{c}}\approx10^{18.5}$ g/s); or (II) the X-rays in the plateau state are dominated by emission from the base of the jet and not the accretion disk (e.g. via inverse Compton scattering from the outflow).Comment: 9 pages, 7 figures, accepted in A&

Radio emission of the Galactic X-rays binaries with relativistic jets

Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI+61o303, GRS 1915+10 and some others. We also reviewed some data from the GBI monitoring program at two frequencies and hard X-ray BATSE (20-100 keV) and soft X-ray RTXE (2-12 keV) ASM data. We confirmed that flaring radio emission of Cyg X-3 correlated with hard and anti-correlated with soft X-ray emission during the strong flare (>$Jy) in May 1997. During two orbital periods we investigated radio light curves of the remarkable X-binary LSI+61o303. Two flaring events near a phase 0.6 of the 26.5-day orbital period have been detected for first time at four frequencies simultaneously. Powerful flaring events of SS433 were detected at six frequencies in May 1996 and in May 1999. The decay of the flare is exactly fitted by an exponential law and the rate of the decay$\tau$ depends upon frequency as tau \propto \nu^{-0.4} in the first flare and does not depend upon frequency in the second flare, and is equal to \tau=6+-1 days at frequencies from 0.96 to 21.7 GHz in the last flare in May 1999. Many flaring RJXB show two, exponential and power, laws of flare decay. Moreover, these different laws could be present in one or several flares and commonly flare decays are faster at a higher frequency. The decay law seems to change because of geometric form of the conical hollow jets. The synchrotron and inverse Compton losses could explain general frequency dependences in flare evolution. In conclusion we summarized the general radio properties of RJXB.Comment: 10 pages, LaTeX, 14 Postscript figures, talk given at the Gamov Memorial International Conference (GMIC'99) "Early Universe: Cosmological Problems and Instrumental Technologies" in St.Petersburg, 23-27 August, 1999, to appear in Astron. Astrophys. Trans., 200

A weak compact jet in a soft state of Cygnus X-1

We present evidence for the presence of a weak compact jet during a soft X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change, showing the hard state jet to be suppressed by a factor of about 3-5 in radio flux and unresolved to direct imaging observations (i.e. < 1 mas at 4 cm). High time-resolution X-ray observations with the RXTE-PCA were also taken during the radio monitoring period, showing the source to make the transition from the hard state to a softer state (via an intermediate state), although the source may never have reached the canonical soft state. Using astrometric VLBI analysis and removing proper motion, parallax and orbital motion signatures, the residual positions show a scatter of ~0.2 mas (at 4 cm) and ~3 mas (at 13 cm) along the position angle of the known jet axis; these residuals suggest there is a weak unresolved outflow, with varying size or opacity, during intermediate and soft X-ray states. Furthermore, no evidence was found for extended knots or shocks forming within the jet during the state transition, suggesting the change in outflow rate may not be sufficiently high to produce superluminal knots.Comment: Accepted in MNRAS; 4 figures and 1 tabl

Opening angles, Lorentz factors and confinement of X-ray binary jets

We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (less than 10 degrees). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean greater than 10, comparable to those estimated for AGN and much higher than the commonly-assumed values for X-ray binaries of 2 to 5. Jet power constraints do not in most cases rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably XTE J1550-564 and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed.Comment: 11 pages, 4 figures (2 colour), accepted for publication in MNRA

A transient relativistic radio jet from Cygnus X-1

We report the first observation of a transient relativistic jet from the canonical black hole candidate, Cygnus X-1, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN). The jet was observed in only one of six epochs of MERLIN imaging of the source during a phase of repeated X-ray spectral transitions in 2004 Jan--Feb, and this epoch corresponded to the softest 1.5-12 keV X-ray spectrum. With only a single epoch revealing the jet, we cannot formally constrain its velocity. Nevertheless, several lines of reasoning suggest that the jet was probably launched 0.5-4.0 days before this brightening, corresponding to projected velocities of 0.2c < v_app < 1.6c, and an intrinsic velocity of > 0.3c. We also report the occurrence of a major radio flare from Cyg X-1, reaching a flux density of ~120 mJy at 15 GHz, and yet not associated with any resolvable radio emission, despite a concerted effort with MERLIN. We discuss the resolved jet in terms of the recently proposed 'unified model' for the disc-jet coupling in black hole X-ray binaries, and tentatively identify the 'jet line' for Cyg X-1. The source is consistent with the model in the sense that a steady jet appears to persist initially when the X-ray spectrum starts softening, and that once the spectral softening is complete the core radio emission is suppressed and transient ejecta / shock observed. However, there are some anomalies, and Cyg X-1 clearly does not behave like a normal black hole transient in progressing to the canonical soft / thermal state once the ejection event has happened.Comment: Accepted for publication in MNRA

The first resolved imaging of milliarcsecond-scale jets in Circinus X-1

We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ~20 milliarcseconds, corresponding to a physical scale of ~150 au at the assumed distance of 7.8 kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be less than 20 degrees. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultra-relativistic (Lorentz factor >15) flow previously inferred to exist in this system.Comment: Accepted for publication in MNRAS Letters. 6 pages, 4 figure