Jet Axis Research Articles

Impact of jets on kilonova photometric and polarimetric emission from binary neutron star mergers

ABSTRACT A merger of binary neutron stars creates heavy unstable elements whose radioactive decay produces a thermal emission known as a kilonova. In this paper, we predict the photometric and polarimetric behaviour of this emission by performing 3D Monte Carlo radiative transfer simulations. In particular, we choose three hydrodynamical models for merger ejecta, two including jets with different luminosities and one without a jet structure, to help decipher the impact of jets on the light curve and polarimetric behaviour. In terms of photometry, we find distinct colour evolutions across the three models. Models without a jet show the highest variation in light curves for different viewing angles. In contrast to previous studies, we find models with a jet to produce fainter kilonovae when viewed from orientations close to the jet axis, compared to a model without a jet. In terms of polarimetry, we predict relatively low levels (≲0.3–0.4 per cent) at all orientations that, however, remain non-negligible until a few days after the merger and longer than previously found. Despite the low levels, we find that the presence of a jet enhances the degree of polarization at wavelengths ranging from 0.25 to $2.5\rm{\mu m}$, an effect that is found to increase with the jet luminosity. Thus, future photometric and polarimetric campaigns should observe kilonovae in blue and red filters for a few days after the merger to help constrain the properties of the ejecta (e.g. composition) and jet.

Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sqrt{s_{_text {NN}}}=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 text {pb}^{-1} of pp collisions collected in 2017 and 1.4 text {nb}^{-1} of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-k_{t} algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R= 0.2 and R= 0.4, and only R= 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R= 0.2 jets are also measured using 1.7 text {nb}^{-1} of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, R_text {AA}, is calculated for both b-jets and inclusive jets with R= 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet R_text {AA} to inclusive jet R_text {AA} is also presented and suggests that the R_text {AA} for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.

DC magnetic field-assisted improvement of textile dye degradation efficiency with multi-capillary air bubble discharge plasma jet.

Axial DC magnetic field-assisted multi-capillary underwater air bubble discharge plasma jet has been used to study the productions of reactive oxygen species. Analyses of optical emission data revealed that the rotational (Tr) and vibrational temperatures (Tv) of plasma species slightly increased with magnetic field strength. The electron temperature (Te) and density (ne) increased almost linearly with magnetic field strength. Te increased from 0.53 to 0.59eV, whereas ne increased from 1.03 × 1015cm-3 to 1.33 × 1015cm-3 for B = 0 to B = 374 mT, respectively. Analytical results from the plasma treated water provided that the electrical conductivity (EC), oxidative reduction potential (ORP), and the concentrations of O3 and H2 O2 enhanced from 155 to 229 µS cm-1, 141 to 17mV, 1.34 to 1.92mg L-1, and 5.61 to 10.92mg L-1 due to the influence of axial DC magnetic field, while [Formula: see text] reduced from 5.10 to 3.93 for 30min treatment of water with B = 0 and B = 374 mT, respectively. The model wastewater prepared with Remazol brilliant blue textile dye and the plasma treated wastewater studied by optical absorption spectrometer, Fourier transform infrared spectrometer, and gas chromatography mass spectrometer. The results show that the decolorization efficiency increased ~ 20% after 5min treatment for the maximum B = 374 mT with respect to zero-magnetic field and, power consumption, and electrical energy cost reduced ~ 6.3% and ~ 4.5%, respectively, due to the maximum assisted axial DC magnetic field strength of 374 mT.

Combined two-photon optical connectivity and planar laser induced fluorescence for instantaneous characterisation of liquid interface during primary atomisation

A technique that combines two-photon excitation (TPE), planar laser induced fluorescence (PLIF) and optical connectivity (OC) has been applied to capture the instantaneous geometry of a cross-section normal to the main direction of the core of a liquid jet exposed to a crossflow of air during atomisation. This paper demonstrates that a nanosecond pulse laser can excite two-photon fluorescence in an atomising Rhodamine B-dyed water jet. It shows that TPE-PLIF on its own has limitations to capture the liquid interface during air-crossflow atomisation. The combination of TPE-PLIF and TPE-OC excites TPE-fluorescence at a targeted cross-section normal to the liquid jet axis at a fixed distance from the liquid jet exit and eliminates the limitations of the individual techniques. The optimisation of the instrumentation of the combined techniques and the associated image processing are described and the quantification of the instantaneous cross-section structures, developing during atomisation, on the surface of the liquid jet is demonstrated.

Flow measurements of jet impingement upon a semicylinder with crossflow

In this work, time-resolved particle image velocimetry (TR-PIV) measurements have been carried out to investigate the structural features of a submerged transverse round liquid turbulent jet discharged into a confined laminar crossflow. The duct Reynolds number based on crossflow velocity is fixed at Re=3000, and the impinging jet is directed to a semicylindrical concave surface located in one of the walls of a vertical square duct. The spatial development and flow dynamics are analyzed along several orthogonal planes parallel/perpendicular to the jet axis for jet Reynolds numbers based on the jet exit diameter of Rej=3000, 6000 and 9000 (jet-to-crossflow velocity ratios of r=3.27, 6.53 and 9.80), respectively. For this purpose, mean and ensemble-averaged velocity and vorticity distributions, turbulent statistics, and Reynolds shear stresses are obtained for various injection rates. Spectral analysis reveals the shedding frequencies of the wake vortices, and the pairing and breakup processes of the evolving large-scale coherent structures have been related to the measured wake Strouhal numbers. Our results indicate that due to the curvature of the target surface and the upwash of the jet impact, the size of coherent structures decreases with increase in the value of Rej. Proper orthogonal decomposition (POD) of the flow using the snapshot method is applied to extract the dominant features of the turbulent flow. It is observed that at the symmetry plane and for Rej=3000, 6000 and 9000, the energy collected by the first two dominant eddies contribute to 14.98%, 18.68%, and 17.89% of the turbulence kinetic energy, respectively. Our results show that the evolution of the time-resolved temporal coefficients of degenerate pairs of modes (1, 2) represent the flapping motion of the jet. Moreover, the amplitude of the oscillations of the flapping jet and the complexity of the flow structure increase for increasing values of Rej.

Jet thermalization in QCD kinetic theory

We perform numerical studies in the framework of QCD kinetic theory to investigate the energy and angular profiles of a high energy parton — as a proxy for a jet produced in heavy ion collisions — passing through a Quark-Gluon Plasma (QGP). We find that the fast parton loses energy to the plasma mainly via a radiative turbulent quark and gluon cascade that transports energy locally from the jet down to the temperature scale where dissipation takes place. In this first stage of the system time evolution, the angular structure of the turbulent cascade is found to be relatively collimated. However, when the lost energy reaches the plasma temperature it is rapidly transported to large angles w.r.t. the jet axis and thermalizes. We investigate the contribution of the soft jet constituents to the total jet energy. We show that for jet opening angles of about 0.3 rad or smaller, the effect is negligible. Conversely, larger opening angles become more and more sensitive to the thermal component of the jet and thus to medium response. Our result showcases the importance of the jet cone size in mitigating or enhancing the details of dissipation in jet quenching observables.

AGN feeding and feedback in M84: from kiloparsec scales to the Bondi radius

ABSTRACT We present the deepest Chandra observation to date of the galaxy M84 in the Virgo Cluster, with over 840 ks of data provided by legacy observations and a recent 730 ks campaign. The increased signal-to-noise ratio allows us to study the origins of the accretion flow feeding the supermassive black hole in the centre of M84 from the kiloparsec scales of the X-ray halo to the Bondi radius, RB. Temperature, metallicity, and deprojected density profiles are obtained in four sectors about M84’s active galactic nucleus (AGN), extending into the Bondi radius. Rather than being dictated by the potential of the black hole, the accretion flow is strongly influenced by the AGN’s bipolar radio jets. Along the jet axis, the density profile is consistent with ne ∝ r−1; however, the profiles flatten perpendicular to the jet. Radio jets produce a significant asymmetry in the flow, violating a key assumption of Bondi accretion. Temperature in the inner kiloparsec is approximately constant, with only a slight increase from 0.6 to 0.7 keV approaching RB, and there is no evidence for a temperature rise imposed by the black hole. The Bondi accretion rate $\dot{M}_{\rm B}$ exceeds the rate inferred from AGN luminosity and jet power by over four orders of magnitude. In sectors perpendicular to the jet, $\dot{M}_{\rm B}$ measurements agree; however, the accretion rate is >4σ lower in the North sector along the jet, likely due to cavities in the X-ray gas. Our measurements provide unique insight into the fuelling of AGN responsible for radio mode feedback in galaxy clusters.

Thermographic 3D particle tracking velocimetry for turbulent gas flows

Turbulent flows are characterized by diverse and unsteady three-dimensional (3D) features that require 3D measurements to study. In case of non-isothermal flows, combined 3D measurements of temperature and velocity are necessary. In this paper, a thermographic 3D particle tracking velocimetry (thermographic 3D-PTV) concept is introduced for simultaneous 3D temperature and velocity measurements in turbulent gas flows. It is based on sub-micron thermographic phosphor particles seeded into the flow as flow tracers with low response times of a few microseconds. To obtain each tracer’s position and velocity, the measurement region is illuminated volumetrically using a double-pulse green laser and Mie-scattered light is imaged by four double-frame cameras. Following the pinhole model-based calibration of all cameras, 3D particle positions are computed for both laser pulse-times using a fast minimum line of sight reconstruction code. Three-component velocities are derived from tracking individual particles between these time steps. For simultaneous 3D thermometry, temperature dependent luminescence emissions from the same phosphor particles are exploited. These emissions are excited using a UV laser synchronized with the first green laser pulse and imaged using two cameras equipped with spectral filters for ratiometric phosphor thermometry. As a result, instantaneous 3D fields of discrete temperature and velocity measurements are obtained throughout the volume. The concept is demonstrated in a turbulent heated gas jet emerging from a circular nozzle at a particle image concentration of 0.005 particle per pixel, where the symmetry of the velocity and temperature distributions about the jet axis is successfully reconstructed.

Monitoring of the polarized H2O maser emission around the massive protostars W75N(B)-VLA 1 and W75N(B)-VLA 2

Context. Several radio sources have been detected in the high-mass star-forming region W75N(B), with the massive young stellar objects VLA 1 and VLA 2 shown to be of particular interest among them. These objects are thought to be at different evolutionary stages: VLA 1 is in the early stage of photoionization and driving a thermal radio jet, while VLA 2 is a thermal, collimated ionized wind surrounded by a dusty disk or envelope. In both sources, 22 GHz H2O masers have been detected in the past. Those around VLA 1 show a persistent linear distribution along the thermal radio jet, while those around VLA 2 have traced the evolution from a non-collimated to a collimated outflow over a period of ∼20 yr. The magnetic field inferred from the H2O masers has shown an orientation rotation following the direction of the major-axis of the shell around VLA 2, whereas it is immutable around VLA 1. Aims. By monitoring the polarized emission of the 22 GHz H2O masers around both VLA 1 and VLA 2 over a period of six years, we aim to determine whether the H2O maser distributions show any variation over time and whether the magnetic field behaves accordingly. Methods. The European VLBI Network was used in full polarization and phase-reference mode in order to determine the absolute positions of the 22 GHz H2O masers with a beam size of ∼1 mas and to determine the orientation and the strength of the magnetic field. We observed four epochs separated by two years from 2014 to 2020. Results. We detected polarized emission from the H2O masers around both VLA 1 and VLA 2 in all the epochs. By comparing the H2O masers detected in the four epochs, we find that the masers around VLA 1 are tracing a nondissociative shock originating from the expansion of the thermal radio jet, while the masers around VLA 2 are tracing an asymmetric expansion of the gas that is halted in the northeast where the gas likely encounters a very dense medium. We also found that the magnetic field inferred from the H2O masers in each epoch can be considered as a portion of a quasi-static magnetic field estimated in that location rather than in that time. This allowed us to study the morphology of the magnetic field around both VLA 1 and VLA 2 locally across a larger area by considering the vectors estimated in all the epochs as a whole. We find that the magnetic field in VLA 1 is located along the jet axis, bending toward the north and south at the northeasterly and southwesterly ends of the jet, respectively, reconnecting with the large-scale magnetic field. The magnetic field in VLA 2 is perpendicular to the expansion directions until it encounters the denser matter in the northeast, where the magnetic field is parallel to the expansion direction and agrees with the large-scale magnetic field. We also measured the magnetic field strength along the line of sight in three of the four epochs, with resulting values of −764 mG < B||VLA 1 < − 676 mG and −355 mG < B||VLA 2 < −2426 mG.

Heat transfer investigation on under-expanded supersonic impinging jets

In this study, wall-resolved large-eddy simulations are performed to investigate the underpinning physics of impingement heat transfer in under-expanded supersonic impinging jets. The jet is generated with an infinite-lipped nozzle of diameter D, has a nozzle-to-wall distance of 5D, a nozzle pressure ratio (NPR) of 3.4 and a Reynolds number of 6×104 based on the ideally-expanded jet velocity. Two thermal boundary conditions of a heated isothermal wall and an adiabatic wall for the impingement plate are considered.Both impinging jets in the current study feature a strong stand-off shock, which oscillates periodically in front of the impingement plate at two dominant frequencies. These oscillations result in two local peaks of the mean heat transfer coefficients with the first peak located in the stagnation region but shifted away from the stagnation point (i.e. jet axis), whilst the second peak is located in the wall jet region. The instantaneous fields of pressure, vorticity and Nusselt number are first discussed to study qualitatively the connection between these two peaks of the mean heat transfer coefficient and the near-wall flow structures. The characteristics of these two peaks are then analysed using the near-wall statistics and spectra of the pressure, axial velocity and Nusselt number distribution.It is found that the first peak of the Nusselt number forms as a consequence of the jet impingement of the non-periodic turbulent structures, whilst the second peak is linked to the reattachment of the recirculation bubble in the wall jet. It is shown that the unsteady separation and reattachment processes are strongly related to the oscillatory motion of the stand-off shock at the dominant frequencies. Last but not the least, the first local minimum close to the stagnation point is also found to be associated with the strong oscillatory behaviour of the stand-off shock.

Technological process of field crops spraying with slotted sprayers

BACKGROUND: The subject of the study is the technological process of spraying field crops with slotted sprayers and the indicators dispersion.
 AIMS: Improving the technological process of spraying plants with the use of pneumo-hydraulic slotted sprayers.
 METHODS: Special equipment was used for photographing films of the liquid being sprayed under various operating modes of slotted sprayers with the possibility of calculating the size of the droplets. Fulfillment of the requirements for the number of drops/cm2 at the treated object, overlapping the liquid spray jets ensures uniform distribution of drops over the spraying width. Therefore, it was sufficient to have information about the fragmentation of the thickness of the liquid film along the axis of the nozzle spray liquid into drops and obtaining their quantity per unit time depending on the flow rate of the working fluid.
 Newness of the research lies in determining the effective operation of slotted sprayers as part of the spraying device.
 RESULTS: With the use of the special equipment, it is possible to fulfill agrotechnical requirements for droplet sizes. When using herbicides for foliar post-emergence treatment with a systemic pesticide, the limits of MMD range are from 226 m to 400 m. Soil herbicide treatment with a systemic pesticide requires an increased droplet MMD range of 401 m to 500 m and 500 m. The number of drops/cm2 when using fungicides is limited from 50 to 70, insecticides from 20 to 30, and herbicides from 20 to 40.
 CONCLUSIONS: The applied technology makes it possible to reduce the consumption of preparations and working fluid with high work performance and resource saving. The above research results can be used as the basis for determining the effective technology of a boom sprayer with slotted liquid sprayers. Fulfillment of the requirements for the number of drops/cm2 at the treatment facility overlapping liquid spray torches ensures a uniform distribution of drops over the spraying width. Therefore, it suffices to know about the division of the thickness of the liquid film along the axis of the liquid spray jet into drops and to obtain their number per unit time.

Insights from the first winter weather observations near Mount Everest's summit

Insights from the first winter weather observations near Mount Everest's summit

Particle image velocimetry of supersonic jets with micro vortex generators

The flow field of supersonic jets with micro vortex generators (MVGs) is investigated using Particle Image Velocimetry (PIV) to shed light on the noise reduction mechanisms associated with such devices. Recently, MVG nozzles have been developed as a new noise reduction technology through the collaboration between the University of Cincinnati and the Naval Research Laboratory. MVGs were implemented on model scale nozzles representative of GE F404 engine nozzles, and noise reductions up to −6 dB have been observed in both microphone measurements and LES simulations. The PIV measurements of the flow field reveal that the MVGs alter the shock cell spacing and strengths in the jet plume and substantially reduce the mean axial velocity at the jet axis. In addition, streamwise vortices generated by MVGs enhance shear layer mixing and redistributes turbulence along the shear layer to narrower regions. The measured flow field quantities are extracted to explain flow field changes on the noise reductions observed in the acoustic far field.

On different modes of a filamentary atmospheric pressure plasma jet: modeling, laser schlieren deflectometric and high-speed camera investigations

We investigated a filamentary non-thermal atmospheric pressure plasma jet used for coating applications. The plasma jet exhibits two different modes, the stationary mode and the locked mode, in which the filaments rotate around the plasma jet axis. We present a model for the modes and verify it by measurements with high-speed camera and laser schlieren deflectometry. Laser schlieren deflectometry investigations reveal a drift of the rotation frequency over time towards lower values. Additionally, relations between the filament rotation frequency and gas flow as well as input power, respectively, are investigated by the laser schlieren deflectometry. Correlation between rotation frequency and gas flow show a linear dependence and with increasing power the rotation frequency increases as well. All the results are in agreement with the proposed model.Graphical abstract

Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

The importance of jet noise for prospective supersonic transport (SST) in takeoff and climb modes dictates the need to develop methods for reducing jet noise and their subsequent validation in large- and full-scale tests. This paper presents the results of Russia’s first ground acoustic tests of a rectangular nozzle with a noise suppression system, installed on a subsonic aircraft engine to demonstrate the technology. The authors studied a rectangular beveled nozzle with an ejector and screens—elements of the SST airframe. The test results were compared for three nozzle geometries: a round nozzle corresponding to measurements for the original engine without modifications, a rectangular nozzle without screens, and a rectangular nozzle with screens. It was found that when the rectangular nozzle without screens is used, there two opposite effects occur: noise amplification compared to the round nozzle for angles of observation close to the jet axis, and noise attenuation at angles of observation close to the fan rotation plane. Installing screens increases noise up to 5 dB in the low-frequency region below 150 Hz and reduces noise by 2 dB for frequencies higher than 250 Hz. Estimation of community noise in the EPNL metric showed that this rectangular nozzle with the noise suppression system has the effect of reducing community noise in comparison with the baseline round nozzle.

Experimental investigation and numerical modeling for induction fans

Induced ventilation systems have been widely used in the design of underground space architecture; they are used to agitate the air and eliminate the smoke and harmful gases formed by fire. In the application design of induced ventilation systems, most people often use the Computational Fluid Dynamics (CFD)-technique to simulate and study the flow distribution in underground space buildings. However, there has been little research carried out on the performance of the induction fan, which is a key equipment of induced ventilation systems, especially a lack of experimental verification data on the simulation model of the induction fan. In this paper, the performance of a specific type of axial induction fan is measured experimentally, modeled in CFD. The velocity boundary condition method was adopted for the modeling, and the k-w SST model was adopted for the turbulence model. The CFD model is validated using experimental data on velocity distribution along the axis of the fan jet. The experimental results show that, in addition to wind speed along the jet direction, the axial flow induction fan also has a large deflection wind speed in the y and z directions of 3D space at the outlet. The simulation results show that, along the jet direction, within 1.0 m from the fan outlet, when the efflux induced fan outlet was set to Uniform Wind Speed (UWS), Non-Uniform Wind Speed (NUWS) and Spatial Three-Dimensional Wind Speed (STDWS), the simulation results on average velocity along the jet axis were significantly different from the experimental values. At x = 1.0 m, the agreement between the STDWS simulation results and experimental values is about 183% higher than that of NUWS. With the development of the jet flow, the simulation results of UWS are basically consistent with those of NUWS, and the simulation results of STDWS are significantly better than those of UWS and NUWS, which are closer to the experimental values. At the far end of the jet, the three simulation values are in good agreement with the actual measured values, and the simulation values of STDWS are closer to the actual measured values.

A Unified Model for Bipolar Outflows from Young Stars: Apparent Magnetic Jet Acceleration

We explore a new, efficient mechanism that can power toroidally magnetized jets up to two to three times their original terminal velocity after they enter a self-similar phase of magnetic acceleration. Underneath the elongated outflow lobe formed by a magnetized bubble, a wide-angle free wind, through the interplay with its ambient toroid, is compressed and accelerated around its axial jet. The extremely magnetic bubble can inflate over its original size, depending on the initial Alfvén Mach number M A of the launched flow. The shape-independent slope ∂v r /∂r = 2/3t is a salient feature of the self-similarity in the acceleration phase. Peculiar kinematic signatures are observable in the PV diagrams and can combine with other morphological signatures as probes for density-collimated jets arising in toroidally dominated magnetized winds. The apparent second acceleration is powered by the decrease of the toroidal magnetic field but operates far beyond the scales of the primary magnetocentrifugal launch region and the free asymptotic terminal state. Rich implications may connect the jets arising from the youngest protostellar outflows such as HH 211 and HH 212 and similar systems with parsec-scale jets across the mass and evolutionary spectra.

Configuration of the global magnetic field in AGN parsec-scale jets

ABSTRACT The magnetic field plays a significant role in the phenomenon of highly collimated jets of active galactic nuclei (AGN). Relativistic effects prevent the direct reconstruction of the magnetic field direction as transverse to electric vectors on radio maps. We determined the topology of the B-field by modelling the transverse distributions of the total and linearly polarized intensity, polarization degree, and deviation of the polarization direction from the local jet axis and by further comparison with observational data. We consider (i) a helical field with a different twist angle and (ii) a toroidal field on the jet axis surrounded by a sheath with a longitudinal field. In the latter scenario, we consider different sheath thickness relative to the spine. We assumed the sheath velocity is equal to or less than that of the spine. The relativistic effects have been considered for a general case, under which the axis and velocity vector of the jet and radial directions do not coincide. Our simulations reproduce the main features of the observed transverse profiles of polarization characteristics in parsec-scale AGN jets. The model transverse distribution shapes of the polarization properties are found to be strongly influenced by kinematic and geometric parameters of an outflow. We demonstrated it for three AGNs having different but typical polarization patterns revealed on radio maps. For each of these objects, we identified the model parameters that provide a qualitative correspondence of theoretical profiles with those obtained from observations, indicating that the B-field is strongly ordered on parsec scales.

Explosion risk analysis of R290 leakage into a limited external space

R290 is considered as a promising alternative refrigerant to be used in household air conditioners. To promote the safety application of R290 in air conditioners, a numerical model of refrigerant leakage and diffusion in a limited space was developed, and the reliability of the model was verified by the experimental results on the concentration field of refrigerant leakage from a split air conditioner indoor unit. On this basis, the field strength characteristics of R290 leaking from holes with different diameters and shapes to the external space were investigated, and the explosion risk caused by R290 leakage was further analyzed. The results showed that when R290 leaked from circular leakage holes with different diameters or leakage holes with different shapes to the external space, respectively, Mach disks were formed in the flow area, and the location and size of the Mach disks had certain differences. For circular leakage holes, with the increase of the leakage diameter, the diameter of the Mach disk inside the flow area and the distance from the Mach disk to the leakage hole increased, and the range of the flammable area formed by the leaked R290 in the external space did not change significantly in the horizontal direction, but increased significantly in the vertical direction, which were 0.42 m, 0.84 m, 1.26 m, and 1.7 m, respectively. For leakage holes with the same area but different shapes, the diameter of the Mach disk formed by the gas leaking from the circular hole was larger, and the gas was distributed symmetrically in the horizontal direction with the jet axis as the center in the external space. The gas leaking from the triangular hole was approximately distributed in a triangular shape, and then it diffused along the three centerlines of the triangle. The gas leaking from the square hole diffused along the diagonal of the square in the horizontal direction, and finally the flow area gradually changed from a square to a circle. The gas leaking from the rectangular slit was elliptically distributed in the external space, and the gas mainly diffused along the long axis direction of the ellipse, and the diffusion of the short axis direction was not significant. The range of the flammable area formed by the gas leaking from holes of different shapes did not change significantly in the external space.

The Event Horizon Telescope Image of the Quasar NRAO 530

We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ∼20 μas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ∼5%–8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 μas along a position angle ∼ −28°. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin.