Axisymmetric magnetohydrodynamic simulations have been applied to investigate (1) the interrelation between a central stellar magnetosphere and stellar wind with a surrounding magnetized disk ...outflow, and (2) how the overall formation of a large scale jet is affected by that. The initial magnetic field distribution applied is a superposition of two components-the stellar dipole and the surrounding disk magnetic field-in either parallel or antiparallel alignment. Correspondingly, the mass outflow is launched as stellar wind plus disk wind. Our simulations evolve from an initial state in hydrostatic equilibrium with an initially force-free magnetic field configuration. Due to differential rotation between star and disk, a strong toroidal magnetic field component is induced. The stellar dipole inflates and opens up on large scale. Stellar wind and disk wind may evolve in a pair of collimated outflows. However, the existence of a reasonably strong disk wind component is essential for collimation. The classical disk jet, as known from previous numerical studies, becomes less collimated due to the pressure of the central stellar wind. In some simulations we observe the generation of strong flares triggering a sudden change in the outflow mass loss rate (or velocity) by a factor of two, accompanied by a redistribution in the radial profile of momentum flux and jet velocity across the jet. We discuss the hypothesis that these flares may trigger internal shocks in the asymptotic jets which are observed as knots.
Context. The neutrino event IceCube−170922A appears to originate from the BL Lac object TXS 0506+056. To understand the neutrino creation process and to localize the emission site, we studied the ...radio images of the jet at 15 GHz. Aims. Other BL Lac objects show properties similar to those of TXS 0506+056, such as multiwavelength variability or a curved jet. However, to date only TXS 0506+056 has been identified as neutrino emitter. The aim of this paper is to determine what makes the parsec-scale jet of TXS 0506+056 specific in this respect. Methods. We reanalyzed and remodeled 16 VLBA 15 GHz observations between 2009 and 2018. We thoroughly examined the jet kinematics and flux-density evolution of individual jet components during the time of enhanced neutrino activity between September 2014 and March 2015, and in particular before and after the neutrino event. Results. Our results suggest that the jet is very strongly curved and most likely observable under a special viewing angle of close to zero. We may observe the interaction between jet features that cross each other’s paths. We find subsequent flux-density flaring of six components passing the likely collision site. In addition, we find a strong indication for precession of the inner jet, and model a precession period of about 10 yr via the Lense-Thirring effect. We discuss an alternative scenario, which is the interpretation of observing the signature of two jets within TXS 0506+056, again hinting toward a collision of jetted material. We essentially suggest that the neutrino emission may result from the interaction of jetted material in combination with a special viewing angle and jet precession. Conclusions. We propose that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings seem capable of explaining the neutrino generation at the time of a low gamma-ray flux and also indicate that TXS 0506+056 might be an atypical blazar. It seems to be the first time that a potential collision of two jets on parsec scales has been reported and that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.
On 2019/07/30.86853 UT, IceCube detected a high-energy astrophysical neutrino can-didate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 percent uncertainty region of the event. ...Our analysis of 15 GHz Very Long Baseline Ar-ray (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after theIceCube event, reveals evidence for a radio ring structure which develops with time.Several arc-structures evolve perpendicular to the jet ridge line. We find evidence forprecession of a curved jet based on kinematic modelling and a periodicity analysis.An outflowing broad line region (BLR) based on the C IV line emission (Sloan Dig-ital Sky Survey, SDSS) is found. We attribute the atypical ring to an interaction ofthe precessing jet with the outflowing material.We discuss our findings in thecontext of a spine-sheath scenario where the ring reveals the sheath andits interaction with the surroundings (NLR clouds).We find that the radioemission is correlated with theγ-ray emission, with radio lagging theγ-rays. Basedon theγ-ray variability timescale, we constrain theγ-ray emission zone to the BLR(30-200rg) and within the jet launching region. We discuss that the outflowing BLRprovides the external radiation field forγ-ray production via external Compton scat-tering.The neutrino is most likely produced by proton-proton interactionin the blazar zone (beyond the BLR), enabled by episodic encounters ofthe jet with dense clouds, i.e. some molecular cloud in the NLR.
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 swirling jet in the quasar 1308+326 Britzen, S.; Qian, S.-J.; Steffen, W. ...
Astronomy and astrophysics (Berlin),
06/2017, Letnik:
602
Journal Article
Recenzirano
Odprti dostop
Context. Despite numerous and detailed studies of the jets of active galactic nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most ...prominent unsolved problems, as is the launching mechanism of jets in AGN. The quasar 1308+326 (z = 0.997) allows us to study the overall properties of its jet in detail and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the Monitoring Of Jets in Active galactic nuclei with Very Long Baseline Array (VLBA) experiments (MOJAVE)⋆⋆ survey permit us to trace out the structural changes in 1308+326 that we present here. The long-lived jet features in this source can be followed for about two decades. Aims. We investigate the very long baseline interferomety (VLBI) morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. Methods. Fifty VLBA observations performed at 15 GHz from the MOJAVE survey were re-modeled with Gaussian components and re-analyzed (the time covered: 20 Jan. 1995–25 Jan. 2014). The analysis was supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5 GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. Results. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position-angle (EVPA) rotation, we conclude that the jet of 1308+326 has a helical structure, meaning that the components are moving along helical trajectories and the trajectories themselves are also experiencing a precessing motion. A model of a precessing nozzle was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data till 2012 are consistent with a swing period of 16.9 yr. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, which is disturbed by the tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. Conclusions. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet that is pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound-up filamentary structures are found. They are all related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a “component” comprises plasma tracing the magnetic field, which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation.
Protostellar jets most probably originate in turbulent accretion disks surrounding young stellar objects. We investigate the evolution of a disk wind into a collimated jet under the influence of ...magnetic diffusivity, assuming that the turbulent pattern in the disk will also enter the disk corona and the jet. Using the ZEUS-3D code in the axisymmetry option we solve the time-dependent resistive MHD equations for a model setup of a central star surrounded by an accretion disk. The disk is taken as a time-independent boundary condition for the mass flow rate and the magnetic flux distribution. We derive analytical estimates for the magnitude of magnetic diffusion in a protostellar jet connecting our results to earlier work in the limit of ideal MHD. We find that the diffusive jets propagate slower into the ambient medium, most probably due to the lower mass flow rate in the axial direction. Close to the star we find that a quasi stationary state evolves after several hundred (weak diffusion) or thousand (strong diffusion) disk rotations. Magnetic diffusivity affects the protostellar jet structure as follows. The jet poloidal magnetic field becomes de-collimated. The jet velocity increases with increasing diffusivity, while the degree of collimation for the hydrodynamic flow remains more or less the same. We suggest that the mass flux is a proper tracer for the degree of jet collimation and find indications of a critical value for the magnetic diffusivity above which the jet collimation is only weak. We finally develop a self-consistent picture in which all these effects can be explained in the framework of the Lorentz force.
Neben protektiven Eigenschaften können Schutzhandschuhe zur Auslösung und Unterhaltung von Kontaktekzemen an den Händen beitragen. Im 10-Jahreszeitraum von 2002 - 2011 wurden n = 1.555 ...Epikutantestungen mit patienteneigenen Schutzhandschuhmaterialien bei 292 Patienten mit V.a. handschuhassoziierte Hauterscheinungen parallel zur Epikutantestung kommerzieller Testallergene der DKG-Testreihen Standard, Gummioder Lederallergene durchgeführt. 48 Patienten reagierten positiv auf wenigstens einen eigenen Handschuh, von diesen reagierten 26 (54%) zusätzlich auf kommerzielle handschuhassoziierte Testallergene, während bei 22 (46%) die Verdachtsdiagnose ausschließlich durch positive Testergebnisse auf eigene Handschuhe gesichert werden konnte. Unterschiedliche Handschuhmaterialien wiesen unterschiedliche Reaktionshäufigkeiten (Anzahl der positiven Epikutantestreaktionen pro getestete Handschuhproben einer Materialgruppe) von 2 - 100% auf. Für nitrilgetränkte Baumwollhandschuhe und Nitrilhandschuhe zeigte sich bei Paralleltestung von Handschuhproben in Alkohol (Alk) und Wasser (Aqu) ein höherer Sensibilisierungsnachweis bei Verwendung von Alk als Testvehikel, während für Handschuhe aus Material- Mix (Stoff, Leder, Gummi), Gummi ohne nähere Angabe, NRL oder Vinyl abhängig vom individuellen Handschuh z.T. der Sensibilisierungsnachweis nur unter Verwendung von Alk oder Aqu als Testvehikel möglich war. Bei diesen Materialen erscheint eine Paralleltestung sinnvoll.*Erstpuplikation in Allergologie, Jahrgang 38, Nr. 7/2015, S. 346-355, mit freundlicher Genehmigung der Autoren.
Context. NGC 4258 is a well known spiral galaxy with a peculiar large scale jet flow detected in the radio and in Hα. Due to the special geometry of the galaxy, the jets emerge from the nuclear ...region through the galactic disk – at least in the inner region. Aims.Also the distribution of molecular gas looks different from that in other spiral galaxies: 12CO(1–0) emission has only been detected in the center and along the jets and only up to distances of about $50\hbox{$^{\prime\prime}$}$ (1.8 kpc) from the nucleus. This concentration of CO along the jets is similar to what is expected as fuel for jet-induced star formation in more distant objects. The reason for the CO concentration along the inner jets in NGC 4258 was not understood and is the motivation for the observations presented here. Methods.Using the IRAM interferometer at Plateau de Bure, we mapped the 12CO(1–0) emission of the central part of NGC 4258 along the nuclear jet direction in the inner 3 kpc. In order to get a properly positioned overlay with Hα we observed NGC 4258 in Hα at the Hoher List Observatory of the University of Bonn. Results. We detected two parallel CO ridges along a position angle of $-25^\circ$ with a total length of about $80\hbox{$^{\prime\prime}$}$ (2.8 kpc), separated by a CO depleted funnel with a width of about $5\hbox{$^{\prime\prime}$}$ (175 pc). The Hα emission is more extended and broader than the CO emission with its maximum just in between the two CO ridges. It seems to be mixed in location and in velocity with the CO emission. In CO we see a peculiar velocity distribution in the iso-velocity map and p-v diagrams. We discuss different scenarios for an interpretation and present a model which can explain the observational results consistently. Conclusions. We propose here that the concentration of CO along the ridges is due to interaction of the rotating gas clouds with the jet's magnetic field by ambipolar diffusion (ion-neutral drift). This magnetic interaction is thought to increase the time the molecular clouds reside near the jet thus leading to the quasi-static CO ridge.
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