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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 are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession1due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star2. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow3, although the 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 time scale 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 changing jet orientation can be modelled as the Lense–Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate4. 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 environment5,6. The relativistic jets associated with the black-hole X-ray binary system V404 Cygni change their orientation on time scales of minutes to hours, implying that the direction of the jets is being affected by the dynamics of the surrounding accretion flow that powers them.

Observational constraints of the relativistic jets from black holes have largely come from the most powerful and extended jets, leaving the nature of the low-luminosity jets a mystery. M81∗is one of the nearest low-luminosity jets and it emitted an extremely large radio flare in 2011, allowing us to study compact core emission with unprecedented sensitivity and linear resolution. Using a multiwavelength campaign, we were able to track the flare as it re-brightened and became optically thick. Simultaneous X-ray observations indicated that the radio re-brightening was preceded by a low-energy X-ray flare at least 12 days earlier. Associating the time delay (tdelay) between the two bands with the cooling time in a synchrotron flare, we find that the magnetic field strength was 1.9 < B < 9.2 G, which is consistent with magnetic field estimate from spectral energy distribution modelling, B < 10.2 G. In addition, Very Long Baseline Array observations at 23 GHz clearly illustrate a discrete knot moving at a low relativistic speed of vapp/c = 0.51 ± 0.17 associated with the initial radio flare. The observations indicate radial jet motions for the first time in M81∗. This has profound implications for jet production, as it means radial motion can be observed in even the lowest-luminosity AGN, but at slower velocities and smaller radial extents (≍104RG).

We present new Spitzer Infrared Spectrograph (IRS) observations of three intermediate polars: V1223 Sgr, EX Hya, and V603 Aql. We detected a strong, fading flare event from V1223 Sgr. During this event, the flux declined by a factor of 13 in 30 minutes. Given the similarity in the slope of its mid-infrared spectrum during this event to that of AE Aqr, we suggest that this event was caused by transient synchrotron emission. Thus, V1223 Sgr becomes the third cataclysmic variable known to be a synchrotron source. We were unable to confirm the mid-infrared excess noted by Harrison et al. (Paper I) for EX Hya, suggesting that this object is either not a synchrotron source, or is slightly variable. Due to a very high background, V603 Aql was not detected in the long-wavelength regions accessible to the IRS. Given the recent detection of SS Cygni at radio wavelengths during outburst, we extract archival Spitzer IRS spectra for this source obtained during two successive maxima. These spectra do not show a strong excess, but without simultaneous data at shorter wavelengths, it is not possible to determine whether there is any contribution to the mid-infrared fluxes from a synchrotron jet.

We report high-resolution radio imaging of the recurrent nova RS Ophiuchi (RS Oph) during the first month of the 2006 outburst, using the Very Long Baseline Array (VLBA). Observations made on days 20.8 and 26.8 of the outburst show a synchrotron-emitting partial shell that is much brighter to the east than to the west. Assuming that the broad component of the infrared lines corresponds to the outermost part of the shell seen by the VLBA, the distance to the source is 2.45 +- 0.4 kpc. The circular shape and spectral indices of the shell emission challenge simple models for the radio structure immediately after the outburst. The second epoch also shows an additional, resolved, synchrotron-emitting component well to the east of the shell. Its inferred velocity is comparable to the escape speed from the surface of a high-mass white dwarf. This component was not seen in the first epoch. Its appearance may be related to the outflow reaching the edge of the nebula created by the red giant wind, which had been refilling the void left by the last outburst in 1985. This eastern component is likely related to the jets previously seen in this and other symbiotic stars, and it represents the earliest clear detection of such a jet, as well as the best case yet for synchrotron emission from a white dwarf jet.

We report strict upper limits to the radio luminosities of three neutron star low-mass X-ray binaries obtained with the Very Large Array while they were in hard X-ray states as observed with the Rossi X-Ray Timing Explorer: 1E 1724-307, 4U 1812-12, and SLX 1735-269. We compare these upper limits to the radio luminosities of several black hole binaries in very similar hard states and find that the neutron star systems are as faint as or fainter than all of the black hole candidates. The differences in luminosities can partly be attributed to the lower masses of the neutron star systems, which on theoretical and observational grounds are expected to decrease the radio luminosities as M0.8. However, there still remains a factor of 30 scatter in the radio luminosities of black hole and neutron star X-ray binaries, particularly at X-ray luminosities of a few percent Eddington. We find no obvious differences in the X-ray timing and spectral properties that can be correlated with the radio luminosity. We discuss the implications of these results on current models for the relationship between accretion and jets.

We present radio imaging observations of the 1998 outburst of the peculiar emission-line star CI Cam, taken ~1, 4, 75, 82, 93, 163, and 306 days after the beginning of the 1998 March 31.64 X-ray flare. The first two epochs show a resolved but compact (no larger than 12 mas) radio source that becomes optically thin at frequencies higher than 5 GHz. The spectrum and brightness temperatures are consistent with synchrotron self-absorption, although free-free absorption may also play a role. The later images show a large (120-350 mas) oval-shaped or double-ring remnant. The radio spectrum combined with the high brightness temperature indicates that the emission is synchrotron, while the morphology suggests that this is powered by a decelerating shock moving through dense circumstellar material produced by a strong stellar wind. The radio images of CI Cam are equally well fitted by an expanding ellipsoid or two expanding rings; the former gives Th [?] 4.2(t - 50,904.1)0.77, with Th the major axis in milliaarcseconds and t the Modified Julian Date (MJD). The corresponding expansion speed in the plane of the sky was ~12,000 km s-1 over the first few days (for an assumed distance of 5 kpc), slowing by a factor of ~3 by the time of the last observation almost a year later. The radio emission from all other X-ray binary transients is either unresolved or takes the form of highly collimated relativistic jets. We suggest that CI Cam represents a rare case in which these jets were smothered early on by the unusually dense circumstellar medium. In this model, CI Cam is the analog to extragalactic supernovae formed by the collapsar mechanism, while the more usual X-ray binaries with relativistic jets are analogous to the jets that escape those supernovae to form a subset of g-ray bursts.

We present the long-term X-ray light curves and detailed spectral and timing analyses of XTE J1908+094 using the Rossi X-Ray Timing Explorer Proportional Counter Array observations covering two outbursts in 2002 and early 2003. At the onset of the first outburst, the source was found in a spectrally low/hard state lasting for ~40 days, followed by a 3 day long transition to the high/soft state. The source flux (in 2-10 keV) reached ~100 mcrab on 2002 April 6, then decayed rapidly. In power spectra, we detect strong band-limited noise and varying low-frequency quasi-periodic oscillations that evolved from ~0.5 to ~5 Hz during the initial low/hard state of the source. We find that the second outburst closely resembled the spectral evolution of the first. The X-ray transient's overall outburst characteristics led us to classify XTE J1908+094 as a black hole candidate. Here we also derive precise X-ray position of the source using Chandra observations that were performed during the decay phase of the first outburst and following the second outburst.

Multifrequency observations from the Very Large Array, Very Long Baseline Array (VLBA), and Owens Valley Radio Observatory Millimeter Array of a major radio outburst of Cygnus X-3 in 2001 September are presented, measuring the evolution of the spectrum of the source over 3 decades in frequency, over a period of 6 days. Following the peak of the flare, as the intensity declines the high-frequency spectrum at frequency n steepens from n-0.4 to n-0.6, after which the spectral index remains at this latter terminal value, a trend previously observed but hitherto not satisfactorily explained. VLBA observations, for the first time, track over several days the expansion of a sequence of knots whose initial diameters are ~8 mas. The light-crossing time within these plasmons is of the same order as the timescale over which the spectrum is observed to evolve. We contend that properly accounting for light-travel time effects in and between plasmons that are initially optically thick but that after expansion become optically thin explains the key features of the spectral evolution, for example, the observed timescale. Using the VLBA images, we have directly measured for the first time the proper motions of individual knots, analysis of which shows a two-sided jet whose axis is precessing. The best-fit jet speed is b ~ 0.63, and the precession period is ~5 days, significantly lower than that fitted for a previous flare. Extrapolation of the positions of the knots measured by the VLBA back to zero separation shows this to occur approximately 2.5 days after the detection of the rise in flux density of Cyg X-3.

The High Energy Gamma Ray Astronomy (HEGRA) Cerenkov telescope array group recently reported a steady and extended unidentified TeV gamma-ray source lying at the outskirts of Cygnus OB2. This is the most massive stellar association known in the Galaxy, estimated to contain ~2600 OB-type members alone. It has been previously argued that the large-scale shocks and turbulence induced by the multiple interacting supersonic winds from the many young stars in such associations may play a role in accelerating Galactic cosmic rays. Indeed, Cyg OB2 also coincides with the nonvariable MeV-GeV range unidentified EGRET source, 3EG 2033+4118. We report on the near-simultaneous follow-up observations of the extended TeV source region with the Chandra X-Ray Observatory and the Very Large Array radio telescope, obtained in order to explore this possibility. Analysis of the CO, H I, and IRAS 100 mm emissions shows that the TeV source region coincides with an outlying subgroup of powerful OB stars that have evacuated or destroyed much of the ambient atomic, molecular, and dust material and that may be related to the very high energy emissions. An interesting supernova-remnant-like structure is also revealed near the TeV source region in the CO, H I, and radio emission maps. Applying a numerical simulation that accurately tracks the radio to gamma-ray emission from primary hadrons as well as primary and secondary e+-, we find that the broadband spectrum of the TeV source region favors a predominantly nucleonic--rather than electronic--origin for the high-energy flux, although deeper X-ray and radio observations will help confirm this. A very reasonable, ~0.1%, conversion efficiency of Cyg OB2's extreme stellar wind mechanical luminosity to nucleonic acceleration to ~PeV (1015 eV) energies is sufficient to explain the multifrequency emissions.

Very Long Baseline Array images of the X-ray binary Cygnus X-3 were obtained 2, 4, and 7 days after the peak of a 10 Jy flare on 1997 February 4. The first two images show a curved one-sided jet, and the third shows a scatter-broadened disk, presumably at the position of the core. The jet curvature changes from the first to the second epoch, which strongly suggests a precessing jet. The ratio of the flux density in the approaching jet to that in the (undetected) receding jet is [?]330; if this asymmetry is due to Doppler boosting, the implied jet speed is [?]0.81c. Precessing-jet model fits, together with the assumption that the jet is intrinsically symmetric and was ejected during or after the major flare, yield the following constraints: the jet inclination to the line of sight must be [?]14deg, the cone opening angle must be [?]12deg, and the precession period must be [?]60 days.

We describe a new protocol deployed at the National Radio Astronomy Observatory’s Karl G. Jansky Very Large Array (VLA) to support the distribution of data in support of commensal data analysis. The protocol, vys, is designed to provide access to a high time resolution data stream while a primary observation continues with the typical (lower) time resolution data stream. This form of dual time resolution, commensal observing has been implemented to enable the search for millisecond astrophysical transient events by a new, dedicated compute cluster located at the VLA. The fast transient detection system, realfast, performs real-time analysis in situto detect events of interest and record relatively short duration data “cut-outs” of those events. By selectively recording high time resolution data, provided by vysat rates of up to 1.4GBs−1, realfastwill reduce the recorded data volume by an estimated factor of up to 1000. This makes it possible to search for transients commensally in a high data rate stream over the thousands of hours needed to find the rarest events.