Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network we have made a precise measurement of the radio parallax of the black hole Xray binary MAXI J1820+070, providing a model-independent distance to the source. Our parallax measurement of (0.348 ± 0.033) mas for MAXI J1820+070 translates to a distance of (2.96 ± 0.33) kpc. This distance implies that the source reached (15 ± 3) per cent of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity and the mass of the black hole in MAXI J1820+070 to be (63 ± 3) • , (0.89 ± 0.09) c and (9.2 ± 1.3) M , respectively.

The evolution of massive stars is influenced by the mass lost to stellar winds over their lifetimes. These winds limit the masses of the stellar remnants (such as black holes) that the stars ultimately produce. We use radio astrometry to refine the distance to the black hole X-ray binary Cygnus X-1, which we find to be 2.22−0.17+0.18 kiloparsecs. When combined with archival optical data, this implies a black hole mass of 21.2 ± 2.2 solar masses, higher than previous measurements. The formation of such a high-mass black hole in a high-metallicity system (within the Milky Way) constrains wind mass loss from massive stars.

We present new radio, optical, and X-ray observations of three Ultraluminous X-ray sources (ULXs) that are associated with large-scale nebulae. We report the discovery of a radio nebula associated with the ULX IC342 X-1 using the Very Large Array (VLA). Complementary VLA observations of the nebula around Holmberg II X-1, and high-frequency Australia Telescope Compact Array (ATCA) and Very Large Telescope (VLT) spectroscopic observations of NGC5408 X-1 are also presented. We study the morphology, ionization processes, and the energetics of the optical/radio nebulae of IC342 X-1, Holmberg II X-1 and NGC5408 X-1. The energetics of the optical nebula of IC342 X-1 is discussed in the framework of standard bubble theory. The total energy content of the optical nebula is 6 × 10 52 erg. The minimum energy needed to supply the associated radio nebula is 9.2 × 10 50 erg. In addition, we detected an unresolved radio source at the location of IC342 X-1 at VLA scales. However, our Very Long Baseline Interferometry (VLBI) observations using the European VLBI Network likely rule out the presence of any compact radio source at milli-arcsecond (mas) scales. Using a simultaneous Swift X-ray Telescope measurement, we estimate an upper limit on the mass of the black hole in IC342 X-1 using the "fundamental plane" of accreting black holes and obtain M BH ≤ (1.0 ± 0.3) × 10 3 M ⊙ . Arguing that the nebula of IC342 X-1 is possibly inflated by a jet, we estimate accretion rates and efficiencies for the jet of IC342 X-1 and compare with sources like S26, SS433, IC10 X-1.

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them should be affected by the dynamics of the flow, which in accreting stellarmass black holes has shown increasing evidence for precession 1 due to frame dragging effects that occur when the black hole spin axis is misaligned with the orbital plane of its companion star 2 . Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow 3 , although the full interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation on a timescale of minutes to hours in the black hole X-ray binary V404 Cygni, detected with very long baseline interferometry during the peak of its 2015 outburst.We show that this can be modelled as Lense-Thirring precession of a vertically-extended slim disk that arises from the super-Eddington accretion rate 4 . Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly-accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets, and distributing the black hole feedback more uniformly over the surrounding environment 5, 6 .During the 2015 outburst 7 of the black hole X-ray binary system V404 Cygni 8 , we conducted high-angular resolution radio monitoring with the Very Long Baseline Array (VLBA). Our obser-3 vations (Extended Data Table 1) spatially resolved the jets in this system, on size scales of up to 5 milliarcseconds (12 a.u. at the known distance of 2.39 ± 0.14 kpc 9 ; see examples in Figure 1).These jets evolved in both morphology and brightness on timescales of minutes.The orientation of the jets on the plane of the sky varied between epochs, ranging between −30.6°and +5.6°east of north (Figure 1, 2, and Extended Data Table 2). This range encompasses the orientation inferred from the position angle of the linearly-polarised radio emission 10 measured during the 1989 outburst (−16 ± 6°east of north; we state all uncertainties at 68% confidence) 11 .Moreover, during a period of intense radio and sub-millimetre flaring on June 22nd 12 , we observed multiple ejection events spanning a similar range of orientations over a single four-hour observation ( Figure 1), implying extremely rapid changes in the jet axis.The time-resolved images from June 22nd (see Supplementary Video) show a series of ballistically-moving ejecta that persist for tens of minutes before fading below the detection threshold of ≈ 10 mJy. The radio emission is dominated by a stationary core that is always present, allowing us to perform relative astrometry on the ejecta. The ejecta appear on both sides of the core, with prop...