Jet Collimation Research Articles

Dynamic formation of stable current-driven plasma jets

Instabilities play a prominent role in determining the inherent structure and properties of magnetized plasma jets spanning both laboratory and astrophysical settings. The manner in which prominent unstable modes dynamically evolve remains key to understanding plasma behavior and control. In astrophysical phenomena, self-similar jets are observed to propagate over vast distances while avoiding breakup caused by unstable mode growth. However, the production of stable dense plasma jets in the laboratory has been limited by the onset of unstable modes that restrict jet lifetime, collimation, and scalability. In this work, we visualize the formation of stable laboratory-generated, dense, super-magnetosonic plasma jets in real time, and we identify an underlying mechanism that contributes to this behavior. The current-driven plasma jets generated in our experiments form a flowing Z-pinch, which is generally unstable to the m = 1 kink instability. Our results indicate that a stable dense plasma jet can be maintained for timescales over which a steady pinch current can be sustained, even at levels which would otherwise lead to rapid unstable mode growth and resultant pinch disassembly.

Faraday Rotation in the Jet of M87 inside the Bondi Radius: Indication of Winds from Hot Accretion Flows Confining the Relativistic Jet

Abstract We study Faraday rotation in the jet of M87 inside the Bondi radius using eight Very Long Baseline Array data sets, one at 8 GHz, four at 5 GHz, and three at 2 GHz. We obtain Faraday rotation measures (RMs) measured across the bandwidth of each data set. We find that the magnitude of RM systematically decreases with increasing distance from 5000 to 200,000 Schwarzschild radii. The data, showing predominantly negative RM signs without significant difference of the RMs on the northern and southern jet edges, suggest that the spatial extent of the Faraday screen is much larger than the jet. We apply models of hot accretion flows, thought to be prevalent in active galactic nuclei with a relatively low luminosity such as M87, and find that the decrease of RM is described well by a gas density profile . This behavior matches the theoretically expected signature of substantial winds, nonrelativistic un-collimated gas outflows from hot accretion flows, which is consistent with the results of various numerical simulations. The pressure profile inferred from the density profile is flat enough to collimate the jet, which can result in gradual acceleration of the jet in a magneto-hydrodynamical process. This picture is in good agreement with the observed gradual collimation and acceleration of the M87 jet inside the Bondi radius. The dominance of negative RMs suggests that the jet and wind axis are misaligned such that the jet emission exposes only one side of the toroidal magnetic fields permeating the winds.

Generation of collimated electron jets from plasma under applied electromagnetostatic field

AbstractThe collimated electron jets ejected from cylindrical plasma are produced in particle-in-cell simulation under the applied longitudinal magnetostatic field and radial electrostatic field, which is a process that can be conveniently performed in a laboratory. We find that the applied magnetostatic field contributes significantly to the jet collimation, whereas the applied electrostatic field plays a vital role in the jet formation. The generation mechanism of collimated jets can be well understood through energy gain of the tagged electrons, and we conclude that the longitudinal momentum of the electrons is converted from the transverse momentum via the transverse-induced magnetic field. It has been found that the ejecting velocity of the jets is close to the speed of light when the applied electrostatic field reaches 3 × 1010 V/m. The present scheme may also give us an insight into the formation of astrophysical jets in celestial bodies.

Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342

Abstract We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multifrequency Very Long Baseline Array observations. This source is known as the nearest γ-ray emitting radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating that the jet is continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical shape. The location of the “collimation break” is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance on the order of ∼100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting a coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy γ-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile of the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial in this source and NLS1s in general.

Axial plasma jet characterization on a microsecond x-pinch

The jets produced on a microsecond x-pinch (quarter period T1/4 ∼ 1 μs, dI/dt ∼ 0.35 kA/ns) have been studied through light-field schlieren imaging and optical framing photographs across 4 different materials: Al, Ti, Mo, and W. The axial velocity of the jets was measured and exhibited no dependence on atomic number (Z) of the wire material. There may be a dependence on another factor(s), namely, the current rise rate. The average axial jet velocity across all four materials was measured to be 2.9 ± 0.5 × 106 cm/s. The average jet diameter and the average radial jet expansion rate displayed inverse relationships with Z, which may be attributed to radiative cooling and inertia. Asymmetry between the anode and cathode jet behavior was observed and is thought to be caused by electron beam activity. The mean divergence angle of the jet was found to vary with wire material and correlated inversely with the thermal conductivity of the cold wire. Optical images indicated a two-layer structure in Al jets which may be caused by standing shocks and resemble phenomena observed in astrophysical jet formation and collimation. Kinks in the jets have also been observed which may be caused by m = 1 MHD instability modes or by the interaction of the jet with the electrode plasma.

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

Understanding the launching, acceleration, and collimation of jets powered by active galactic nuclei remains an outstanding problem in relativistic astrophysics. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very long baseline interferometry that has thus far been able to probe the transverse jet structure in the acceleration and collimation zone of only two sources. Here we report radio interferometric observations of 3C 84 (NGC 1275), the central galaxy of the Perseus cluster, made with an array including the orbiting radio telescope of the RadioAstron mission. The obtained image transversely resolves the edge-brightened jet in 3C 84 only 30 microarcseconds from the core, which is ten times closer to the central engine than what has been possible in previous ground-based observations, and it allows us to measure the jet collimation profile from ~ 100 to ~10000 gravitational radii from the black hole. The previously found, almost cylindrical jet profile on scales larger than a few thousand r_g is now seen to continue at least down to a few hundred r_g from the black hole and we find a broad jet with a transverse radius larger than about 250 r_g at only 350 r_g from the core. If the bright outer jet layer is launched by the black hole ergosphere, it has to rapidly expand laterally on scales smaller than 100 r_g. If this is not the case, then this jet sheath is likely launched from the accretion disk.

Multiwavelength Observations of Relativistic Jets from General Relativistic Magnetohydrodynamic Simulations

This work summarizes a program intended to unify three burgeoning branches of the high-energy astrophysics of relativistic jets: general relativistic magnetohydrodynamic (GRMHD) simulations of ever-increasing dynamical range, the microphysical theory of particle acceleration under relativistic conditions, and multiwavelength observations resolving ever-decreasing spatiotemporal scales. The process, which involves converting simulation output into time series of images and polarization maps that can be directly compared to observations, is performed by (1) self-consistently prescribing models for emission, absorption, and particle acceleration and (2) performing time-dependent polarized radiative transfer. M87 serves as an exemplary prototype for this investigation due to its prominent and well-studied jet and the imminent prospect of learning much more from Event Horizon Telescope (EHT) observations this year. Synthetic observations can be directly compared with real observations for observational signatures such as jet instabilities, collimation, relativistic beaming, and polarization. The simplest models described adopt the standard equipartition hypothesis; other models calculate emission by relating it to current density or shear. These models are intended for application to the radio jet instead of the higher frequency emission, the disk and the wind, which will be subjects of future investigations.

Finding Transitions of Physical Condition in Jets from Observations over the Range of 103–109 Schwarzschild Radii in Radio Galaxy NGC 4261

Abstract We report new measurements of jet width and radiation profiles along jets over the range of 103–109 Schwarzschild radius (R S) in the nearby radio galaxy NGC 4261 using multifrequency Very Long Baseline Array (VLBA) and Very Large Array images. In the VLBA images, we found parabolic-to-conical transition signatures on both the approaching jet and counterjet width profiles at ∼104 R S from the central engine. A transition in the radiation profile along the approaching jet was also found at ∼104 R S clearly. Based on the consistency of the transition locations, we conclude that the physical conditions of the NGC 4261 jets change at this distance. Jet flows that change from accelerating to expanding regions were previously found in M87 and NGC 6251 and are presumably present in NGC 4261. Additionally, we found another transition in the radiation profile at ∼3 × 106 R S in the conical region. NGC 4261 is the first case in which a jet structural transition is suggested in both the approaching and counter jets; this implies that the active galactic nucleus jet collimation process is fundamentally characterized by the global distribution of ambient pressure rather than the local interaction between the jet and the surrounding medium. We discuss the evolution of jet conditions in terms particle acceleration, cooling, dissipation, and jet pressure balance with the surrounding hot gas.

A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud.

Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

The Global Jet Structure of the Archetypical Quasar 3C 273

A key question in the formation of the relativistic jets in active galactic nuclei (AGNs) is the collimation process of their energetic plasma flow launched from the central supermassive black hole (SMBH). Recent observations of nearby low-luminosity radio galaxies exhibit a clear picture of parabolic collimation inside the Bondi accretion radius. On the other hand, little is known of the observational properties of jet collimation in more luminous quasars, where the accretion flow may be significantly different due to much higher accretion rates. In this paper, we present preliminary results of multi-frequency observations of the archetypal quasar 3C 273 with the Very Long Baseline Array (VLBA) at 1.4, 15, and 43 GHz, and Multi-Element Radio Linked Interferometer Network (MERLIN) at 1.6 GHz. The observations provide a detailed view of the transverse structure resolved on a broad range of spatial scales from sub-parsec to kilo parsecs, allowing us to profile the jet width as a function of the distance from the core for the first time in jets of bright quasars. We discovered a transition from a parabolic stream to a conical stream, which has been seen in much lower-luminosity radio galaxies. The similarity in the profile to the much lower-powered radio galaxy M87 suggests the universality of jet collimation among AGNs with different accretion rates.

The Most Compact Bright Radio-loud AGNs. II. VLBA Observations of 10 Sources at 43 and 86 GHz

Abstract Radio-loud active galactic nuclei (AGNs), hosting powerful relativistic jet outflows, provide an excellent laboratory for studying jet physics. Very long baseline interferometry (VLBI) enables high-resolution imaging on milli-arcsecond (mas) and sub-mas scales, making it a powerful tool to explore the inner jet structure, shedding light on the formation, acceleration, and collimation of AGN jets. In this paper, we present Very Long Baseline Array observations of 10 radio-loud AGNs at 43 and 86 GHz that were selected from the Planck catalog of compact sources and are among the brightest in published VLBI images at and below 15 GHz. The image noise levels in our observations are typically 0.3 and 1.5 mJy beam−1 at 43 and 86 GHz, respectively. Compared with the VLBI data observed at lower frequencies from the literature, our observations with higher resolutions (with the highest resolution being up to 0.07 mas at 86 GHz and 0.18 mas at 43 GHz) and at higher frequencies detected new jet components at sub-parsec scales, offering valuable data for studies of the physical properties of the innermost jets. These include the compactness factor of the radio structure (the ratio of core flux density to total flux density), and core brightness temperature ( ). In all these sources, the compact core accounts for a significant fraction ( ) of the total flux density. Their correlated flux density at the longest baselines is higher than 0.16 Jy. The compactness of these sources make them good phase calibrators of millimeter-wavelength ground-based and space VLBI.

Enhancement of Quasistationary Shocks and Heating via Temporal Staging in a Magnetized Laser-Plasma Jet.

We investigate the formation of a laser-produced magnetized jet under conditions of a varying mass ejection rate and a varying divergence of the ejected plasma flow. This is done by irradiating a solid target placed in a 20T magnetic field with, first, a collinear precursor laser pulse (10^{12} W/cm^{2}) and, then, a main pulse (10^{13} W/cm^{2}) arriving 9-19ns later. Varying the time delay between the two pulses is found to control the divergence of the expanding plasma, which is shown to increase the strength of and heating in the conical shock that is responsible for jet collimation. These results show that plasma collimation due to shocks against a strong magnetic field can lead to stable, astrophysically relevant jets that are sustained over time scales 100 times the laser pulse duration (i.e., >70 ns), even in the case of strong variability at the source.

The ALMA Phasing System: A Beamforming Capability for Ultra-high-resolution Science at (Sub)Millimeter Wavelengths

The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) has developed and deployed the hardware and software necessary to coherently sum the signals of individual ALMA antennas and record the aggregate sum in Very Long Baseline Interferometry (VLBI) Data Exchange Format. These beamforming capabilities allow the ALMA array to collectively function as the equivalent of a single large aperture and participate in global VLBI arrays. The inclusion of phased ALMA in current VLBI networks operating at (sub)millimeter wavelengths provides an order of magnitude improvement in sensitivity, as well as enhancements in u–v coverage and north–south angular resolution. The availability of a phased ALMA enables a wide range of new ultra-high angular resolution science applications, including the resolution of supermassive black holes on event horizon scales and studies of the launch and collimation of astrophysical jets. It also provides a high-sensitivity aperture that may be used for investigations such as pulsar searches at high frequencies. This paper provides an overview of the ALMA Phasing System design, implementation, and performance characteristics.

The Konus-Wind Catalog of Gamma-Ray Bursts with Known Redshifts. I. Bursts Detected in the Triggered Mode

Abstract In this catalog, we present the results of a systematic study of gamma-ray bursts (GRBs) with reliable redshift estimates detected in the triggered mode of the Konus-Wind (KW) experiment during the period from 1997 February to 2016 June. The sample consists of 150 GRBs (including 12 short/hard bursts) and represents the largest set of cosmological GRBs studied to date over a broad energy band. From the temporal and spectral analyses of the sample, we provide the burst durations, the spectral lags, the results of spectral fits with two model functions, the total energy fluences, and the peak energy fluxes. Based on the GRB redshifts, which span the range , we estimate the rest-frame, isotropic-equivalent energy, and peak luminosity. For 32 GRBs with reasonably constrained jet breaks, we provide the collimation-corrected values of the energetics. We consider the behavior of the rest-frame GRB parameters in the hardness–duration and hardness–intensity planes, and confirm the “Amati” and “Yonetoku” relations for Type II GRBs. The correction for the jet collimation does not improve these correlations for the KW sample. We discuss the influence of instrumental selection effects on the GRB parameter distributions and estimate the KW GRB detection horizon, which extends to , stressing the importance of GRBs as probes of the early universe. Accounting for the instrumental bias, we estimate the KW GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate, which are in general agreement with those obtained in previous studies.

Exploring jet substructure with jet shapes in ALICE

The characterisation of the jet substructure can give insight into the microscopic nature of the modification induced on high-momentum partons by the Quark-Gluon Plasma that is formed in ultra-relativistic heavy-ion collisions. This modification of parton-to-jet fragmentation and of the parton virtuality, induced by the QGP, can be studied using jet shapes, in particular using jet energy redistribution, intra-jet broadening or collimation. Results of a selected set of jet shapes are presented for p–Pb collisions at sNN=5.02 TeV and for Pb–Pb collisions at sNN=2.76 TeV. Results are also compared with PYTHIA Perugia 11 calculations and models that include in-medium energy loss.

Coronal Jet Collimation by Nonlinear Induced Flows

Abstract Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale of influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma-β. As the shear flow and plasma-β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.

Dynamics of magnetic flux tubes in an advective flow around a black hole

Entangled magnetic fields entering into an accretion flow would very soon be stretched into a dominant toroidal component due to strong differentially rotating motion inside the accretion disc. This is particularly true for weakly viscous, low angular momentum transonic or advective discs. We study the trajectories of toroidal flux tubes inside a geometrically thick flow which undergoes a centrifugal force supported shock. We also study effects of these flux tubes on the dynamics of the inflow and the outflow. We use a finite difference method (Total Variation Diminishing) for this purpose and specifically focussed on whether these flux tubes significantly affect the properties of the outflows such as its collimation and the rate. It is seen that depending upon the cross-sectional radius of the flux tubes which control the drag force, these field lines may move towards the central object or oscillate vertically before eventually escaping out of the funnel wall (pressure zero surfaces) along the vertical direction. A comparison of results obtained with and without flux tubes show these flux tubes could play pivotal role in collimation and acceleration of jets and outflows.

H2O masers and protoplanetary disk dynamics in IC 1396 N

We report H$_2$O maser line observations of the bright-rimmed globule IC 1396 N using a ground-space interferometer with the 10-m RadioAstron radio telescope as the space-based element. The source was not detected on projected baselines >2.3 Earth diameters, which indicates a lower limit on the maser size of L >0.03 AU and an upper limit on the brightness temperature of 6.25 x 10$^{12}$ K. Positions and flux densities of maser spots were determined by fringe rate mapping. Multiple low-velocity features from -4.5 km/s to +0.7 km/s are seen, and two high-velocity features of V$_{LSR}$=-9.4 km/s and +4.4 km/s are found at projected distances of 157 AU and 70 AU, respectively, from the strongest low-velocity feature at V$_{LSR}$=$\sim$0.3 km/s. Maser components from the central part of the spectrum fall into four velocity groups but into three spatial groups. Three spatial groups of low-velocity features detected in the 2014 observations are arranged in a linear structure about 200 AU in length. Two of these groups were not detected in 1996 and possibly are jets which formed between 1996 and 2014. The putative jet seems to have changed direction in 18 years, which we explain by the precession of the jet under the influence of the gravity of material surrounding the globule. The jet collimation can be provided by a circumstellar protoplanetary disk. There is a straight line orientation in the V$_{LSR}$-Right Ascension diagram between the jet and the maser group at V$_{LSR}$=$\sim$0.3 km/s. However, the central group with the same position but at the velocity V$_{LSR}$$\sim$-3.4 km/s falls on a straight line between two high-velocity components detected in 2014. Comparison of the low-velocity positions from 2014 and 1996, based on the same diagram, shows that the majority of the masers maintain their positions near the central velocity V$_{LSR}$=$\sim$0.3 km/s during the 18 year period.

A new view on the M 87 jet origin: Turbulent loading leading to large-scale episodic wiggling

Context. The nearby, giant radio galaxy M 87 hosts a supermassive black hole (BH) and is well-known for a bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large BH mass, M 87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. Many kinematic studies have been performed to determine the proper motions in the jet. Despite M 87 providing all proofs of being an active BH, the apparent jet speed remained puzzling, because proper motion measurements between 15 and 43 GHz for the same region of 1–10 mas core distance provided largely discrepant results. This source is a prime object to be studied in exquisite detail with the upcoming Event Horizon Telescope (EHT) observations because it promises to allow a direct view on the jet launching process itself. Aims. We aim to decipher some of the kinematic puzzles in the pc-scale jet with the analysis we present here.Methods. We re-modeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE program. The data span a time range between Jul. 1995 and May 2011. We performed a detailed investigation of the pc-scale jet kinematics on different timescales, the shortest periods between the observations beeing 10 and 80 days, and in different jet modes, making use of VLBA observations. In addition, we studied the jet ridge line behavior as a function of time. Special care was taken to analyze the region close to the 15 GHz core, and the dynamics and distribution of newly emerging jet features in the jet.Results. We find an indication for apparent superluminal motion in the jet. Moreover, we present evidence for acceleration between 0.5 and 10 mas of core separation. The data suggest that the central part of M 87 at 15 GHz seems to be rotating. Jet components and counter-jet components are ejected in different directions under varying angles, explaining the impression of a broad opening angle. In this paper we present evidence for two different operating modes of the jet of M 87. The jet switches between two phases: i) the jet ridge line is at least double or the jet axis is displaced vertically, and ii) an unperturbed phase where the jet ridge line remains almost straight but is smoothly curved and the jet components are aligned along a classical jet axis. The mode change occurs every couple of years. Between the two operating modes, a transition phase is visible.Conclusions. The M 87 jet visible at 15 GHz probes a different physical zone compared to the standard blazar-zone we tend to see in AGN jets. The most likely scenario explaining the observed phenomena is a turbulent mass loading into the jet, most probably due to local, fast reconnection processes driven by turbulence of a tangled magnetic field, which is either generated in the accretion disk or the disk corona. In addition, on large scales, a global magnetic structure is required to channel the turbulent flow into what evolves into a large-scale jet. Large-scale jet instabilities may explain the curved pattern of the observed jet flow.

A plasma deflagration accelerator as a platform for laboratory astrophysics

The replication of astrophysical flows in the laboratory is critical for isolating particular phenomena and dynamics that appear in complex, highly-coupled natural systems. In particular, plasma jets are observed in astrophysical contexts at a variety of scales, typically at high magnetic Reynolds number and driven by internal currents. In this paper, we present detailed measurements of the plasma parameters within deflagration-produced plasma jets, the scaling of these parameters against both machine operating conditions and the corresponding astrophysical phenomena. Using optical and spectroscopic diagnostics, including Schlieren cinematography, we demonstrate the production of current-driven plasma jets of ∼100 km/s and magnetic Reynolds numbers of ∼100, and discuss the dynamics of their acceleration into vacuum. The results of this study will contribute to the reproduction of various types of astrophysical jets in the laboratory and indicate the ability to further probe active research areas such as jet collimation, stability, and interaction.