Discrete Ejection Research Articles

Constraining the physical properties of large-scale jets from black hole X-ray binaries and their impact on the local environment with blast-wave dynamical models

ABSTRACT Relativistic discrete ejecta launched by black hole X-ray binaries (BH XRBs) can be observed to propagate up to parsec-scales from the central object. Observing the final deceleration phase of these jets is crucial to estimate their physical parameters and to reconstruct their full trajectory, with implications for the jet powering mechanism, composition, and formation. In this paper, we present the results of the modelling of the motion of the ejecta from three BH XRBs: MAXI J1820$+$070, MAXI J1535–571, and XTE J1752–223, for which high-resolution radio and X-ray observations of jets propagating up to $\sim$15 arcsec ($\sim$0.6 pc at 3 kpc) from the core have been published in the recent years. For each jet, we modelled its entire motion with a dynamical blast-wave model, inferring robust values for the jet Lorentz factor, inclination angle and ejection time. Under several assumptions associated to the ejection duration, the jet opening angle and the available accretion power, we are able to derive stringent constraints on the maximum jet kinetic energy for each source (between $10^{43}$ and $10^{44}$ erg, including also H1743–322), as well as placing interesting upper limits on the density of the ISM through which the jets are propagating (from $n_{\rm ISM} \lesssim 0.4$ cm$^{-3}$ down to $n_{\rm ISM} \lesssim 10^{-4}$ cm$^{-3}$). Overall, our results highlight the potential of applying models derived from gamma-ray bursts to the physics of jets from BH XRBs and support the emerging picture of these sources as preferentially embedded in low-density environments.

Formation and Evolution of Transient Jets and Their Cavities in Black Hole X-Ray Binaries

We propose a model explaining the origin of transient/episodic jets in black hole X-ray binaries, in which they are caused by transitions from a collimated, strongly magnetized jet to a wide, uncollimated outflow. The change occurs when the accretion flow leaves the magnetically choked state due to an increase of the accretion rate for a weakly varying magnetic flux. The formed powerful jet then detaches from its base, and propagates as a discrete ejection. The uncollimated outflow then produces a relativistic plasma that fills the surroundings of the black hole, contributing to the formation of a low-density cavity. While the pressure in the cavity is in equilibrium with the surrounding interstellar medium (ISM), its inertia is orders of magnitude lower than that of the ISM. This implies that the plasma cannot efficiently decelerate the ejecta, explaining most of the observations. The modest deceleration within the cavities observed in some cases can then be due to the presence of clouds and/or filaments, forming a wide transition zone between the cavity and the ISM.

Modelling the kinematics of the decelerating jets from the black hole X-ray binary MAXI J1348–630

ABSTRACT Black hole low mass X-ray binaries (BH LMXBs) can launch powerful outflows in the form of discrete ejecta. Observing the entire trajectory of these ejecta allows us to model their motion with great accuracy and this is essential for measuring their physical properties. In particular, observing the final deceleration phase, often poorly sampled, is fundamental to obtain a reliable estimate of the jet’s energy. During its 2019/2020 outburst, the BH LMXB MAXI J1348–630 launched a single-sided radio-emitting jet that was detected at large scales after a strong deceleration due to the interaction with the interstellar medium (ISM). We successfully modelled the jet motion with a dynamical external shock model, which allowed us to constrain the jet initial Lorentz factor $\Gamma _0 = 1.85^{+0.15}_{-0.12}$, inclination angle $\theta = {29.3 }_{-3.2}^{+2.7 }$ deg, and ejection date $t_{\rm ej} = 21.5_{-3.0}^{+1.8}$ (MJD–58500). Under simple assumptions on the jet opening angle and on the external ISM density, we find that the jet has a large initial kinetic energy $E_0 = 4.6^{+20.0}_{-3.4} \times 10^{46}$ erg, far greater than what commonly measured for LMXBs from the jet’s synchrotron emission. This implies that discrete ejecta radiate away only a small fraction of their total energy, which is instead transferred to the environment. The jet power estimate is larger than the simultaneous available accretion power, and we present several options to mitigate this discrepancy. We infer that MAXI J1348–630 is likely embedded in an ISM cavity with internal density $n = 0.0010^{+0.0005}_{-0.0003}$ cm−3 and radius $R_{\rm c} = 0.61^{+0.11}_{-0.09}$ pc, which could have been produced by the system’s previous activity, as proposed for other BH LMXBs.

The black hole transient MAXI J1348–630: evolution of the compact and transient jets during its 2019/2020 outburst

ABSTRACT We present the radio and X-ray monitoring campaign of the 2019/2020 outburst of MAXI J1348–630, a new black hole X-ray binary (BH XRB) discovered in 2019 January. We observed MAXI J1348–630 for ∼14 months in the radio band with MeerKAT and the Australia Telescope Compact Array, and in the X-rays with MAXI and Swift/XRT. Throughout the outburst, we detected and tracked the evolution of compact and transient jets. Following the main outburst, the system underwent at least four hard-state-only re-flares, during which compact jets were again detected. For the major outburst, we observed the rise, quenching and reactivation of compact jets, as well as two single-sided discrete ejecta travelling away from the BH, launched ∼2 months apart. These ejecta displayed the highest proper motion (≳100 mas d−1) ever measured for an accreting BH binary. From the jet motion, we constrain the ejecta inclination and speed to be ≤46○ and ≥0.69 c, and the opening angle and transverse expansion speed of the first component to be ≤6○ and ≤0.05 c. We also infer that the first ejection happened at the hard-to-soft state transition, before a strong radio flare, while the second ejection was launched during a short excursion from the soft to the intermediate state. After travelling with constant speed, the first component underwent a strong deceleration, which was covered with unprecedented detail and suggested that MAXI J1348–630 could be located inside a low-density cavity in the interstellar medium, as already proposed for XTE J1550–564 and H1743–322.

The Mass-loss History of the Red Hypergiant VY CMa*

Abstract Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass-loss events over the past few hundred years. Hubble Space Telescope/Space Telescope Imaging Spectrograph spectroscopy of numerous small knots close to the star allow us to measure their radial velocities from the strong K i emission and determine their separate motions, spatial orientations, and time since ejecta. Their ages concentrate around 70, 120, 200, and 250 yr ago. A K i emission knot only 50 mas from the star ejected as recently as 1985–1995 may coincide with an H2O maser. Comparison with VY CMa’s historic light curve from 1800 to the present shows several knots with ejection times that correspond with extended periods of variability and deep minima. The similarity of this correspondence in VY CMa with the remarkable recent dimming of Betelgeuse and an outflow of gas is apparent. The evidence for similar outflows from the surface of a more typical red supergiant suggests that discrete ejections are more common and surface or convective activity is a major source of mass loss for red supergiants.

The variable radio counterpart of Swift J1858.6-0814

ABSTRACT Swift J1858.6-0814 is a transient neutron star X-ray binary discovered in 2018 October. Multiwavelength follow-up observations across the electromagnetic spectrum revealed many interesting properties, such as erratic flaring on minute time-scales and evidence for wind outflows at both X-ray and optical wavelengths, strong and variable local absorption, and an anomalously hard X-ray spectrum. Here, we report on a detailed radio observing campaign consisting of one observation at 5.5/9 GHz with the Australia Telescope Compact Array, and nine observations at 4.5/7.5 GHz with the Karl G. Jansky Very Large Array. A radio counterpart with a flat to inverted radio spectrum is detected in all observations, consistent with a compact jet being launched from the system. Swift J1858.6-0814 is highly variable at radio wavelengths in most observations, showing significant variability when imaged on 3-to-5-min time-scales and changing up to factors of 8 within 20 min. The periods of brightest radio emission are not associated with steep radio spectra, implying they do not originate from the launching of discrete ejecta. We find that the radio variability is similarly unlikely to have a geometric origin, be due to scintillation, or be causally related to the observed X-ray flaring. Instead, we find that it is consistent with being driven by variations in the accretion flow propagating down the compact jet. We compare the radio properties of SwiftJ1858.6-0814 with those of Eddington-limited X-ray binaries with similar X-ray and optical characteristics, but fail to find a match in radio variability, spectrum, and luminosity.

The appearance of a compact jet in the soft–intermediate state of 4U 1543−47

ABSTRACT Recent advancements in the understanding of jet–disc coupling in black hole candidate X-ray binaries (BHXBs) have provided close links between radio jet emission and X-ray spectral and variability behaviour. In ‘soft’ X-ray states the jets are suppressed, but the current picture lacks an understanding of the X-ray features associated with the quenching or recovering of these jets. Here, we show that a brief, ∼4 d infrared (IR) brightening during a predominantly soft X-ray state of the BHXB 4U 1543−47 is contemporaneous with a strong X-ray type B quasi-periodic oscillation, a slight spectral hardening and an increase in the rms variability, indicating an excursion to the soft–intermediate state (SIMS). This IR ‘flare’ has a spectral index consistent with optically thin synchrotron emission and most likely originates from the steady, compact jet. This core jet emitting in the IR is usually only associated with the hard state, and its appearance during the SIMS places the ‘jet line’ between the SIMS and the soft state in the hardness–intensity diagram for this source. IR emission is produced in a small region of the jets close to where they are launched (∼0.1 light-seconds), and the time-scale of the IR flare in 4U 1543−47 is far too long to be caused by a single, discrete ejection. We also present a summary of the evolution of the jet and X-ray spectral/variability properties throughout the whole outburst, constraining the jet contribution to the X-ray flux during the decay.

Infrared interferometry to spatially and spectrally resolve jets in X-ray binaries

ABSTRACT Infrared interferometry is a new frontier for precision ground-based observing, with new instrumentation achieving milliarcsecond (mas) spatial resolutions for faint sources, along with astrometry on the order of 10 microarcseconds (μas). This technique has already led to breakthroughs in the observations of the supermassive black hole at the Galactic centre and its orbiting stars, active galactic nucleus, and exo-planets, and can be employed for studying X-ray binaries (XRBs), microquasars in particular. Beyond constraining the orbital parameters of the system using the centroid wobble and spatially resolving jet discrete ejections on mas scales, we also propose a novel method to discern between the various components contributing to the infrared bands: accretion disc, jets, and companion star. We demonstrate that the GRAVITY instrument on the Very Large Telescope Interferometer should be able to detect a centroid shift in a number of sources, opening a new avenue of exploration for the myriad of transients expected to be discovered in the coming decade of radio all-sky surveys. We also present the first proof-of-concept GRAVITY observation of a low-mass XRB transient, MAXI J1820+070, to search for extended jets on mas scales. We place the tightest constraints yet via direct imaging on the size of the infrared emitting region of the compact jet in a hard state XRB.

Estimating the Jet Power of Mrk 231 during the 2017–2018 Flare

Abstract Long-term 17.6 GHz radio monitoring of the broad absorption-line quasar, Mrk 231, detected a strong flare in late 2017. This triggered four epochs of Very Long Baseline Array (VLBA) observations from 8.4 to 43 GHz over a 10 week period as well as an X-ray observation with NuSTAR. This was the third campaign of VLBA monitoring that we have obtained. The 43 GHz VLBA was degraded in all epochs, with only 7 of 10 antennas available in three epochs and 8 in the first epoch. However, useful results were obtained due to a fortuitous capturing of a complete, short 100 mJy flare at 17.6 GHz, both growth and decay. This provided useful constraints on the physical model of the ejected plasma that were not available in previous campaigns. We consider four classes of models: discrete ejections (both protonic and positronic) and jetted (protonic and positronic). The most viable model is a “dissipative bright knot” in a faint background leptonic jet with an energy flux ∼1043 erg s−1. Inverse Compton scattering calculations (based on these models) in the ambient quasar photon field explains the lack of a detectable increase in X-ray luminosity measured by NuSTAR. We show that the core (the bright knot) moves toward a nearby secondary at ≈0.97c. The background jet is much fainter. Evidently, the high-frequency VLBA core does not represent the point of origin of blazar jets, in general, and optical depth “core shift” estimates of jet points of origin can be misleading.

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu.

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.

Bennu ejects material from its surface

Asteroids Most asteroids appear inert, but remote observations show that a small number experience mass loss from their surfaces. Lauretta and Hergenrother et al. describe close-range observations of mass loss on the near-Earth asteroid Bennu (see the Perspective by Agarwal). Shortly after arriving at Bennu, navigation cameras on the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security—Regolith Explorer) spacecraft detected objects 1 to 10 centimeters in diameter moving above the surface. Analysis of the objects' trajectories showed that they originated in discrete ejection events from otherwise unremarkable locations on Bennu. Some objects remained in orbit for several days, whereas others escaped into interplanetary space. The authors suggest multiple plausible mechanisms that could underlie this activity. Science , this issue p. [eaay3544][1]; see also p. [1192][2] [1]: /lookup/doi/10.1126/science.aay3544 [2]: /lookup/doi/10.1126/science.aaz7129

A re-establishing jet during an X-ray re-brightening of the Be/X-ray binary Swift J0243.6+6124

Transient Be/X-ray binary systems, wherein a compact object accretes from a Be-companion star, can show giant and periastron outbursts. During the decay of their giant outbursts, some Be/X-ray binaries also show X-ray re-brightenings, the origin of which is not understood. Recently, we presented the discovery of a jet from a neutron star Be/X-ray binary, observed during the giant outburst of Swift J0243.6+6124. Here, we present continued radio monitoring of its 2017/2018 giant outburst decay and a re-brightening of this source. During the former, we observe a radio flare with a steep radio spectrum, possibly caused by interactions between discrete ejecta colliding with the pre-existing jet or the surrounding medium. During the X-ray re-brightening, we observe the radio jet turning on and off within days. Surprisingly, this re-establishing jet is as bright in radio as at the peak of the super-Eddington giant outburst, despite more than two orders of magnitude lower X-ray luminosity. In addition, the jet is only observed when the X-ray luminosity exceeds approximately $2\times 10^{36} (D/5\rm kpc)^2$ erg/s. We discuss how such an X-ray threshold for jet launching might be related to the presence of a magnetic centrifugal barrier at lower mass accretion rates. We also discuss the implications of our results for the launch of jets from strongly magnetized neutron stars, and explore future avenues to exploit the new possibility of coordinated X-ray/radio studies of neutron star Be/X-ray binaries.

A high-contrast imaging survey of nearby red supergiants

AbstractMass-loss in cool supergiants remains poorly understood, but is one of the key elements in their evolution towards exploding as supernovae. Some show evidence of asymmetric mass loss, discrete mass-ejections and outbursts, with seemingly little to distinguish them from more quiescent cases. To explore the prevalence of discrete ejections and companions we have conducted a high-constrast survey using near-infrared imaging and optical polarimetric imaging of nearby southern and equatorial red supergiants, using the extreme adaptive optics instrument SPHERE, which was designed to image planets around nearby stars. We present the initial results of this survey, including the detection of large (500 nm) dust grains in the ejecta of VY CMa and a candidate dusty torus aligned with the maser ring of VX Sgr. We briefly speculate on the consequences for our understanding of mass loss in these extreme stars.

THE ACCRETION FLOW–DISCRETE EJECTION CONNECTION IN GRS 1915+105

ABSTRACT The microquasar GRS 1915+105 is known for its spectacular discrete ejections. They occur unexpectedly, thus their inception has escaped direct observation. It has been shown that the X-ray flux increases in the hours leading up to a major ejection. In this article, we consider the serendipitous interferometric monitoring of a modest version of a discrete ejection described in Reid et al. that would have otherwise escaped detection in daily radio light curves. The observation begins ∼1 hr after the onset of the ejection, providing unprecedented accuracy on the estimate of the ejection time. The astrometric measurements allow us to determine the time of ejection as , i.e., within a precision of 41 minutes (95% confidence). Just like larger flares, we find that the X-ray luminosity increases in last 2–4 hr preceding ejection. Our finite temporal resolution indicates that this elevated X-ray flux persists within minutes of the ejection with 95% confidence, the highest temporal precision of the X-ray–superluminal ejection connection to date. This observation provides direct evidence that the physics that launches major flares occurs on smaller scales as well (lower radio flux and shorter ejection episodes). The observation of a X-ray spike prior to a discrete ejection, although of very modest amplitude, suggests that the process linking accretion behavior to ejection is general from the smallest scales to high luminosity major superluminal flares.

Radio polarimetry as a probe of unresolved jets: the 2013 outburst of XTE J1908+094

XTE J1908+094 is an X-ray transient black hole candidate in the Galactic plane that was observed in outburst in 2002 and 2013. Here we present multifrequency radio and X-ray data, including radio polarimetry, spanning the entire period of the 2013 outburst. We find that the X-ray behaviour of XTE J1908+094 traces the standard black hole hardness–intensity path, evolving from a hard state, through a soft state, before returning to a hard state and quiescence. Its radio behaviour is typical of a compact jet that becomes quenched before discrete ejecta are launched during the late stages of X-ray softening. The radio and X-ray fluxes, as well as the light-curve morphologies, are consistent with those observed during the 2002 outburst of this source. The polarization angle during the rise of the outburst infers a jet orientation in agreement with resolved observations but also displays a gradual drift, which we associate with observed changes in the structure of the discrete ejecta. We also observe an unexpected 90 ◦ rotation of the polarization angle associated with a second component.

THE RATE OF GAS ACCRETION ONTO BLACK HOLES DRIVES JET VELOCITY

Accreting black holes are observed to launch relativistic, collimated jets of matter and radiation. In some sources, discrete ejections have been detected with highly relativistic velocities. These particular sources typically have very high mass accretion rates, while sources lower knot velocities are predominantly associated with black holes with relatively low mass accretion rates. We quantify this behavior by examining knot velocity with respect to X-ray luminosity, a proxy for mass accretion rate onto the black hole. We find a positive correlation between the mass-scaled X-ray luminosity and jet knot velocity. In addition, we find evidence that the jet velocity is also a function of polar angle, supporting the "spine-sheath" model of jet production. Our results reveal a fundamental aspect of how accretion shapes mechanical feedback from black holes into their host environments.

The planetary nebula IPHASXJ211420.0+434136 (Ou5): insights into common-envelope dynamical and chemical evolution

While analysing the images of the IPHAS H$\alpha$ survey, we noticed that the central star of the candidate planetary nebula IPHASXJ211420.0+434136 (also named Ou5) was clearly variable. This is generally considered as an indication of binarity. To confirm it, we performed a photometric monitoring of the central star, and obtained images and spectra of the nebula. The nebular spectrum confirms that IPHASXJ211420.0+434136 is a planetary nebula of moderately high excitation. It has a remarkable morphology with two nested pairs of bipolar lobes, and other unusual features. The light curve of the central star reveals that it is an eclipsing binary system with an orbital period of 8.74 hours. It also displays a strong irradiation effect with an amplitude of 1.5~mag. The presence of multiple bipolar outflows adds constraints to the formation of these nebulae, suggesting the occurrence of discrete ejection events during, or immediately before, the common-envelope phase. IPHASXJ211420.0+434136 also adds evidence to the hypothesis that a significant fraction of planetary nebulae with close binary central stars have a peculiar nebular chemistry and a relatively low nebular mass. This may point to low-mass, low-metallicity progenitors, with additional effects related to the binary evolution. We also suggest that these objects may be relevant to understand the abundance discrepancy problem in planetary nebulae.

The evolving polarized jet of black hole candidate Swift J1745−26

Swift J1745-26 is an X-ray binary towards the Galactic Centre that was detected when it went into outburst in September 2012. This source is thought to be one of a growing number of sources that display "failed outbursts", in which the self-absorbed radio jets of the transient source are never fully quenched and the thermal emission from the geometrically-thin inner accretion disk never fully dominates the X-ray flux. We present multifrequency data from the Very Large Array, Australia Telescope Compact Array and Karoo Array Telescope (KAT- 7) radio arrays, spanning the entire period of the outburst. Our rich data set exposes radio emission that displays a high level of large scale variability compared to the X-ray emission and deviations from the standard radio--X-ray correlation that are indicative of an unstable jet and confirm the outburst's transition from the canonical hard state to an intermediate state. We also observe steepening of the spectral index and an increase of the linear polarization to a large fraction (~50%) of the total flux, as well as a rotation of the electric vector position angle. These are consistent with a transformation from a self-absorbed compact jet to optically-thin ejecta -- the first time such a discrete ejection has been observed in a failed outburst -- and may imply a complex magnetic field geometry.

VLBI observations of the shortest orbital period black hole binary, MAXI J1659−152

The X-ray transient MAXI J1659-152 was discovered by Swift/BAT and it was initially identified as a GRB. Soon its Galactic origin and binary nature were established. There exists a wealth of multi-wavelength monitoring data for this source, providing a great coverage of the full X-ray transition in this candidate black hole binary system. We obtained two epochs of European VLBI Network (EVN) electronic-VLBI (e-VLBI) and four epochs of Very Long Baseline Array (VLBA) data of MAXI J1659-152 which show evidence for outflow in the early phases. The overall source properties (polarization, milliarcsecond-scale radio structure, flat radio spectrum) are described well with the presence of a compact jet in the system through the transition from the hard-intermediate to the soft X-ray spectral state. The apparent dependence of source size and the radio core position on the observed flux density (luminosity dependent core shift) support this interpretation as well. We see no evidence for major discrete ejecta during the outburst. For the source proper motion we derive 2 sigma upper limits of 115 microas/day in right ascension, and 37 microas/day in declination, over a time baseline of 12 days. These correspond to velocities of 1400 km/s and 440 km/s, respectively, assuming a source distance of 7 kpc.

XTE J1752−223 in outburst: a persistent radio jet, dramatic flaring, multiple ejections and linear polarization

The black hole candidate, XTE J1752-223, was discovered in 2009 October when it entered an outburst. We obtained radio data from the Australia Telescope Compact Array for the duration of the ~9 month event. The lightcurves show that the radio emission from the compact jet persisted for the duration of an extended hard state and through the transition to the intermediate state. The flux then rose rapidly by a factor of 10 and the radio source entered a series of at least 7 maxima, the first of which was likely to be emission associated with the compact jet. The subsequent 6 flares were accompanied by variable behaviour in terms of radio spectrum, degree of linear polarisation, morphology and associated X-ray behaviour. They were, however, remarkably similar in terms of the estimated minimum power required to launch such an ejection event. We compare the timing of radio peaks with the location of the ejecta, imaged by contemporaneous VLBI experiments. We then discuss the mechanism behind the events, in terms of whether discrete ejections is the most likely description of the behaviour. One ejection, at least, appears to be travelling with apparent superluminal motion. The range of properties, however, suggests that mutiple mechanisms may be relevant and that at least some of the emission is coming from shocked interactions amongst the ejecta and between the ejecta and the interstellar medium. We also compare the radio flux density with the X-ray source during the hard state and conclude that XTE J1752-223 is a radio-weak/X-ray-bright outlier on the universal correlation for black hole transient sources.