Nearby Jet Research Articles

Discovery of Candidate X-Ray Jets in High-redshift Quasars

Abstract We present Chandra X-ray observations of 14 radio-loud quasars at redshifts 3 < z < 4, selected from a well-defined sample. All quasars are detected in the 0.5–7.0 keV energy band, and resolved X-ray features are detected in five of the objects at distances of 1″–12″ from the quasar core. The X-ray features are spatially coincident with known radio features for four of the five quasars. This indicates that these systems contain X-ray jets. X-ray fluxes and luminosities are measured, and jet-to-core X-ray flux ratios are estimated. The flux ratios are consistent with those observed for nearby jet systems, suggesting that the observed X-ray emission mechanism is independent of redshift. For quasars with undetected jets, an upper limit on the average X-ray jet intensity is estimated using a stacked image analysis. Emission spectra of the quasar cores are extracted and modeled to obtain best-fit photon indices, and an Fe K emission line is detected from one quasar in our sample. We compare X-ray spectral properties with optical and radio emission in the context of both our sample and other quasar surveys.

The Formation and Eruption of a Sigmoidal Filament Driven by Rotating Network Magnetic Fields

Abstract We present the formation and eruption of a sigmoidal filament driven by rotating network magnetic fields (RNFs) near the center of the solar disk, which was observed by the 1 m aperture New Vacuum Solar Telescope at the Fuxian Solar Observatory on 2018 July 12. Counterclockwise RNFs twist two small-scale filaments at their northeastern foot-point region, giving a rotation of nearly 200° within about 140 minutes. The motion of the RNF has a tendency to accelerate at first and then decelerate obviously, as the average rotation speed increased from 10 to 150° hr−1, and then slowed down to 50° hr−1. Coalescence then occurs between filaments F1 and F2. Meanwhile the fine structures in the southwestern region of the filament was involved in another interaction of coalescence. The subsequent EUV brightening due to plasma heating is observed in the two interaction regions. These interacting structures, including F1, F2 and the fine structures in the southwestern region, eventually evolve into a larger-scale sigmoidal filament twisted in the same direction as the RNFs gave. The twist of the sigmoidal filament has exceeded 4π and the filament finally erupted. The motion of the sigmoidal filament remains uniform until a nearby jet collides, causing the filament to erupt faster. These results provide evidence that RNF plays an important role in the formation and eruption of the sigmoidal filament. The phenomena also suggests that the kink instability is the trigger mechanism for the filament eruption.

A transition from parabolic to conical shape as a common effect in nearby AGN jets

ABSTRACT Observational studies of collimation in jets in active galactic nuclei (AGN) are a key to understanding their formation and acceleration processes. We have performed an automated search for jet shape transitions in a sample of 367 AGN using VLBA data at 15 and 1.4 GHz. This search has found 10 out of 29 nearby jets at redshifts z < 0.07 with a transition from a parabolic to conical shape, while the full analysed sample is dominated by distant AGN with a typical z ≈ 1. The ten AGN are UGC 00773, NGC 1052, 3C 111, 3C 120, TXS 0815−094, Mrk 180, PKS 1514+00, NGC 6251, 3C 371, and BL Lac. We conclude that the geometry transition may be a common effect in AGN jets. It can be observed only when sufficient linear resolution is obtained. Supplementing these results with previously reported shape breaks in the nearby AGN 1H 0323+342 and M87, we estimate that the break occurs at 105–106 gravitational radii from the nucleus. We suggest that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. In general, the break point may not coincide with the Bondi radius. The observational data support our model predictions on the jet acceleration and properties of the break point.

Atmospheric blocking and intercomparison of objective detection methods: flow field characteristics

Objective methods for identifying and quantifying atmospheric blocking have been developed over recent decades, primarily targeting North Atlantic blocks. Differences arise from these methods, leading to changes in the resultant blocking climatology. To understand these differences, and better inform future assessments built on quantitative detection of blocks, this paper examines blocking properties produced by three different objective detection algorithms over the global extratropics. Blocking criteria examined include 500 hPa geopotential height anomaly (Z^*), column-averaged potential vorticity anomaly (PV^*), and 500 hPa geopotential height gradient (AGP). Results are analyzed for blocking climatologies and for instantaneous blocking patterns, as well as distributions of block size, speed, duration, and distance traveled. The results emphasize physical characteristics of the flow field and the subsequent blocking regions that emerge; overall, PV^* and Z^* blocked regions often have higher pattern correlation and spatial similarity, though these two methods also display high agreement with AGP in some instances.Z^* finds the largest (and greatest number of) blocked regions, while PV^*-detected regions are smallest in all instances except Southern Hemisphere winter. In some cases, PV^* tracks a nearby jet streak, leading to differences with height-based algorithms. All three algorithms detect some questionable low-latitude blocks that are stationary and persist but do not impair zonal flow, although at different times. Therefore, careful consideration of the algorithm biases is important in future blocking studies. For example, linking extreme weather to detected blocking could vary substantially depending on the algorithm used.

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

Abstract We present the results of Very Large Array NH3 ( J , K ) = ( 1 , 1 ) and ( 2 , 2 ) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig–Haro objects. We report the detection of a new source, NH3–S, in the vicinity of HH 111/HH 121 (∼0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3–S. We also use HCO+ and HCN ( J = 4 − 3 ) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array 13CO, 12CO, and C18O ( J = 2 − 1 ) , N2D+ ( J = 3 − 2 ) , and 13CS ( J = 5 − 4 ) data to gain insight into the nature of NH3–S. The chemical structure of NH3–S shows evidence for “selective freeze-out,” an inherent characteristic of dense cold cores. The inner part of NH3–S shows subsonic nonthermal velocity dispersions indicating a “coherent core,” while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3–S. The properties of NH3–S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig–Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3–S and if/how its evolution is affected by nearby jets.

Unsteadily manipulating internal flow barriers

Typical flows contain internal flow barriers: specialised time-moving Lagrangian entities which demarcate distinct motions. Examples include the boundary between an oceanic eddy and a nearby jet, the edge of the Antarctic circumpolar vortex or the interface between two fluids which are to be mixed together in an microfluidic assay. The ability to control the locations of these barriers in a user-specified time-varying (unsteady) way can profoundly impact fluid transport between the coherent structures which are separated by the barriers. A condition on the unsteady Eulerian velocity required to achieve this objective is explicitly derived, thereby solving an ‘inverse Lagrangian coherent structure’ problem. This is an important first step in developing flow-barrier control in realistic flows, and in providing a postprocessing tool for observational/experimental velocity data. The excellent accuracy of the method is demonstrated using the Kelvin–Stuart cats-eyes flow and the unsteady double gyre, utilising finite-time Lyapunov exponents.

Jet path length dependence in Pb + Pb Collisions with the ATLAS detector

The phenomenon of events containing highly asymmetric dijet pairs is one of the most striking results in heavy ion physics. It has provided the first direct observation of in-medium jet energy loss at the LHC. New results showing the variation of the dijet asymmetry with the angle between the leading jet and the second order Event Plane are presented. This observable effectively probes the path-length dependence of the dijet asymmetry at fixed centrality and can provide a better understanding of the correlation of the parton energy-loss with the underlying geometry. Correlated production of nearby jets is also shown. Two neighbouring jets originating from the same hard scattering should have more similar path lengths in the medium compared to the two jets in the dijet event topology, therefore measuring neighbouring jets may probe differences in quenching that do not result from different path length. The production of nearby jets is quantified using the rate, RΔR, of “neighbouring” jets that accompany “test” jets. The centrality dependence of RΔR as well as the ratios of the RΔR values in collisions of different centrality and the values in the 40–80% centrality range are presented.

Measurement of the production of neighbouring jets in lead–lead collisions at [formula omitted] with the ATLAS detector

This Letter presents measurements of correlated production of nearby jets in Pb+Pb collisions at sNN=2.76 TeV using the ATLAS detector at the Large Hadron Collider. The measurement was performed using 0.14 nb−1 of data recorded in 2011. The production of correlated jet pairs was quantified using the rate, RΔR, of “neighbouring” jets that accompany “test” jets within a given range of angular distance, ΔR, in the pseudorapidity–azimuthal angle plane. The jets were measured in the ATLAS calorimeter and were reconstructed using the anti-kt algorithm with radius parameters d=0.2, 0.3, and 0.4. RΔR was measured in different Pb+Pb collision centrality bins, characterized by the total transverse energy measured in the forward calorimeters. A centrality dependence of RΔR is observed for all three jet radii with RΔR found to be lower in central collisions than in peripheral collisions. The ratios formed by the RΔR values in different centrality bins and the values in the 40–80% centrality bin are presented.

Search for Down-Type Fourth Generation Quarks with the ATLAS Detector in Events with One Lepton and Hadronically DecayingWBosons

This Letter presents a search for pair production of heavy down-type quarks decaying via b' → Wt in the lepton + jets channel, as b'b' → W- tW+ t → bbW+ W- W+ W- → l± νbbqqqqqq. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04 fb(-1) from pp collisions at sqrt[s] = 7 TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.

Magnetic resonance studies of a gas–solids fluidised bed: Jet–jet and jet–wall interactions

Magnetic resonance imaging (MRI) gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features: (1) The interaction between nearby vertical jets from two, three or four orifices; (2) Wall effects, where one or more orifices created vertical jets near the vertical wall of the cylinder containing the particle bed. The results show that nearby jets are mutually attracted. Likewise a jet near a wall bends out of the vertical, towards the wall. For multiple adjacent jets, the jet lengths show dependence on orifice layout: the lengths are in reasonable agreement with published measurements, by other methods, for single jets. The MRI gives three-dimensional images of the single jets and of multiple jets, separate or merging.

A Straight and Narrow Ionized Filament

We report the discovery of a extremely narrow, extremely linear, ionized filament. The filament is 2.5 degrees long and has an H$\alpha$ surface brightness of 0.5 rayleighs. The filament is approximately ``Y'' shaped. The widest separation of the two diagonal segments is 5 arcminutes. We discuss four possible origins for this feature: (1) an extremely low density, nearby jet, (2) an unusually linear filament associated with some large-scale nearby nebula, perhaps even the Local Bubble, (3) an ionized trail left by mechanical input from a star or compact object moving through the ISM, or (4) an ionized trail left by photoionization (``Fossil \stromgren Trail'') from a star or compact object. We favor this last hypothesis, and derive some of the basic properties for an ionized trail. Regardless of whether this latter hypothesis applies to this specific filament, the basic properties of such a trail, its length, width, and brightness, are interesting, predictable, and should be observable behind some white dwarfs. We suggest future tests for ascertaining the origin of this filament, and discuss how this structure might be useful to constrain the thermal and velocity structure of the nearby interstellar medium.

Gravity Wave Excitation by Geostrophic Adjustment of the Jet Stream. Part I: Two-Dimensional Forcing

Abstract A previous study of inertio–gravity wave motions radiating from a two-dimensional ageostrophic Gaussian jet is extended here to a three-dimensional jet source. Fourier integral solutions of the initial-value problem are obtained in analytic form to facilitate comparison with the previous two-dimensional results. For an initial disturbance elongated along the jet axis, the wave solutions near the midpoint are nearly indistinguishable from those obtained in two dimensions and approach those solutions as the jet increases in length. At locations not symmetric with respect to the longitudinal jet axis, inertio–gravity wave structure departs increasingly from the two-dimensional results. In such cases, the early response is determined by the nearby jet structure and exhibits propagation primarily normal to the jet axis. At later times, however, the response is due to the initial disturbance at other locations along the jet axis and reveals a tendency for propagation parallel to the jet. The mean motio...

Raptor responses to low-level jet aircraft and sonic booms

We estimated effects of low-level military jet aircraft and mid- to high-altitude sonic booms (actual and simulated) on nesting peregrine falcons ( Falco peregrinus) and seven other raptors by observing their responses to test stimuli, determining nesting success for the test year, and evaluating site reoccupancy rates for the year following the tests. Frequent and nearby jet aircraft passes: (1) sometimes noticeably alarmed birds, (2) occasionally caused birds to fly from perches or eyries, (3) most often evoked only minimal responses, and (4) were never associated with reproductive failure. Similarly, responses to real and simulated mid- to high-altitude sonic booms were often minimal and never appeared productivity limiting. Eighteen (95%) of 19 nest sites subjected to low-level jet flights and/or simulated sonic booms in 1980 fledged young during that year. Eighteen (95%) of 19 sites disturbed in 1980 were reoccupied by pairs or lone birds of the same species in 1981. We subjected four pairs of prairie falcons ( Falco mexicanus) to low-level aircraft at ad libitum levels during the courtship and incubation phases when adults were most likely to abandon: all four eyries fledged young. From heart rate (HR) data taken via a telemetering egg at another prairie falcon eyrie, we determined that stimulus-induced HR alterations were comparable to rate changes for birds settling to incubate following flight. While encouraging, our findings cannot be taken as conclusive evidence that jet flights and/or sonic booms will have no long-term negative effects for other raptor species or for other areas. In addition, we did not experiment with totally naive wild adults, rotary-winged aircraft, or low-level sonic booms.