We present the detection of a radio-emitting jet from the black-hole candidate and X-ray binary source Cygnus X-1. Evidence of a bright core with a slightly extended structure was found on milliarcsecond resolution observations with the VLBA at 15.4 GHz. Later observations with the VLBA (and including the phased up VLA) at 8.4 GHz show an extended jet-like feature extending to approx. 15 mas from a core region, with an opening angle of < 2 degrees. In addition, lower resolution MERLIN observations at 5 GHz show that the source has < 10 per cent linear polarization. The source was in the low/hard X-ray state during the observations, and the results confirm the existence of persistent radio emission from an unresolved core and a variable relativistic (> 0.6c) jet during this state.Comment: Accepted for publication in MNRA

SS433 is a galactic X-ray binary source, variable across most wavelengths of observation. On arcsecond-scales the radio emission is composed of a bright core and the famous bipolar 'corkscrew' radio jets. A series of MERLIN observations at 5 GHz were taken in 1991 December and 1992 January. The emission from the radio jet was categorized by replacing discrete features with Gaussian flux-density profiles. These fitted components were used to derive proper motions, ejection position-angles and ejection dates for evolving features in the jets. The observed component position-angles and ejection dates were compared to those predicted by the kinematic model of epoch 1989. The position-angle of the precession cone was refined to 98. • 2 ± 0. • 2. A discrepancy was discovered in the observed precessional phase which was leading that of the kinematic model by 7-10 d. This observed discrepancy was in agreement with a transient deviation in precessional phase as measured by the redshifts of optical bullets at a similar time. Analysis of the proper motions of all the fitted components leads to a distance measurement of 4.61 ± 0.35 pc. A pair of symmetrically ejected knots with a velocity much lower than 0.26c were also discovered. Their ejection time overlapped with a period of unusual Doppler shift residuals and fragmentation of optical bullets. These events may represent the first evidence for an interaction between radio components and optical bullets.

We present observations of the X-ray transient XTE J1118+480 during its Low/Hard X-ray state outburst in 2000, at radio and sub-millimetre wavelengths with the VLA, Ryle Telescope, MERLIN and JCMT. The high-resolution MERLIN observations reveal all the radio emission (at 5 GHz) to come from a compact core with physical dimensions smaller than 65*d(kpc) AU. The combined radio data reveal a persistent and inverted radio spectrum, with spectral index \~+0.5. The source is also detected at 350 GHz, on an extrapolation of the radio spectrum. Flat or inverted radio spectra are now known to be typical of the Low/Hard X-ray state, and are believed to arise in synchrotron emission from a partially self-absorbed jet. Comparison of the radio and sub-millimetre data with reported near-infrared observations suggest that the synchrotron emission from the jet extends to the near-infrared, or possibly even optical regimes. In this case the ratio of jet power to total X-ray luminosity is likely to be P_J/L_X >> 0.01, depending on the radiative efficiency and relativistic Doppler factor of the jet. Based on these arguments we conclude that during the period of our observations XTE J1118+480 was producing a powerful outflow which extracted a large fraction of the total accretion power.Comment: Accepted for publication as a Letter in MNRA

We observed the energetic binary Cygnus X-3 in both quiescent and flaring states between 4 and 16 microns using the ISO satellite. We find that the quiescent source shows the thermal free-free spectrum typical of a hot, fast stellar wind, such as from a massive helium star. The quiescent mass-loss rate due to a spherically symmetric, non-accelerating wind is found to be in the range 0.4-2.9 x 10E-4 solar masses per year, consistent with other infrared and radio observations, but considerably larger than the 10E-5 solar masses per year deduced from both the orbital change and the X-ray column density. There is rapid, large amplitude flaring at 4.5 and 11.5 microns at the same time as enhanced radio and X-ray activity, with the infrared spectrum apparently becoming flatter in the flaring state. We believe non-thermal processes are operating, perhaps along with enhanced thermal emission.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure