High-mass microquasars consist of a massive star and a compact object, the latter producing jets that will interact with the stellar wind. The evolution of the jets, and ultimately their radiative outcome, could depend strongly on the inhomogeneity of the wind, which calls for a detailed study. The hydrodynamics of the interaction between a jet and a clumpy wind is studied, focusing on the global wind and single clump-jet interplay. We have performed, using the code \textit{Ratpenat}, three-dimensional numerical simulations of a clumpy wind interacting with a mildly relativistic jet, and of individual clumps penetrating into a jet. For typical wind and jet velocities, filling factors of about > 0.1 are already enough for the wind to be considered as clumpy. An inhomogeneous wind makes the jet more unstable when crossing the system. Kinetic luminosities of the order 1.e37 erg/s allow the jet to reach the borders of a compact binary with an O star, as in the smooth wind case, although with a substantially higher degree of disruption. When able to enter into the jet, clumps are compressed and heated during a time of about their size divided by the sound speed in the shocked clump. Then, clumps quickly disrupt, mass-loading and slowing down the jet. We conclude that moderate wind clumpiness makes already a strong difference with the homogeneous wind case, enhancing jet disruption, mass-loading, bending, and likely energy dissipation in the form of emission. All this can have observational consequences at high-energies and also in the large scale radio jets.

/pdf/3d-simulations-of-microquasar-jets-in-clumpy-stellar-winds-44p5pd4eya.pdf

3D simulations of microquasar jets in clumpy stellar winds

Context. Dense stellar winds may mass-load the jets of active galactic nuclei, although it is unclear on what time and spatial scales the mixing takes place.Aims. Our aim is to study the first steps of the interaction between jets and stellar winds, and also the scales on which the stellar wind mixes with the jet and mass-loads it.Methods. We present a detailed 2D simulation – including thermal cooling – of a bubble formed by the wind of a star designed to study the initial stages of jet-star interaction. We also study the first interaction of the wind bubble with the jet using a 3D simulation in which the star enters the jet. Stability analysis is carried out for the shocked wind structure to evaluate the distances over which the jet-dragged wind, which forms a tail, can propagate without mixing with the jet flow.Results.The 2D simulations point to quick wind bubble expansion and fragmentation after about one bubble shock crossing time. Three-dimensional simulations and stability analysis point to local mixing in the case of strong perturbations and relatively low density ratios between the jet and the jet dragged-wind, and to a possibly more stable shocked wind structure at the phase of maximum tail mass flux. Analytical estimates also indicate that very early stages of the star jet-penetration time may be also relevant for mass-loading. The combination of these and previous results from the literature suggests highly unstable interaction structures and efficient wind-jet flow mixing on the scale of the jet interaction height.Conclusions. The winds of stars with strong mass loss can efficiently mix with jets from active galactic nuclei. In addition, the initial wind bubble shocked by the jet leads to a transient, large interaction surface. The interaction between jets and stars can produce strong inhomogeneities within the jet. As mixing is expected to be effective on large scales, even individual asymptotic giant branch stars can significantly contribute to the mass-load of the jet and thus affect its dynamics. Shear layer mass-entrainment could be important. The interaction structure can be a source of significant non-thermal emission.

/pdf/impact-of-red-giant-agb-winds-on-active-galactic-nucleus-jet-ckewz70efc.pdf

Impact of red giant/AGB winds on active galactic nucleus jet propagation

/pdf/3d-simulations-of-microquasar-jets-in-clumpy-stellar-winds-3hcd6gd311.pdf

We present four radio-loud NLS1 galaxies with extreme emission-line shifts, indicating radial outflow velocities of the ionized gas of up to 2450 km/s, above the escape velocity of the host galaxies. The forbidden lines show strong broadening, up to 2270 km/s. An ionization stratification (higher line shift at higher ionization potential) implies that we see a large-scale outflow rather than single, localized jet-cloud interactions. Similarly, the paucity of zero-velocity [OIII]$\lambda$5007 emitting gas implies the absence of a second narrow-line region (NLR) component at rest, and therefore a large part of the high-ionization NLR is affected by the outflow. Given the radio loudness of these NLS1 galaxies, the observations are consistent with a pole on view onto their central engines, so that the effects of polar outflows are maximized. In addition, a very efficient driving mechanism is required, to reach the high observed velocities. We explore implications from recent hydrodynamic simulations of the interaction between fast winds or jets with the large-scale NLR. Overall, the best agreement with observations (and especially the high outflow speeds of the [NeV] emitting gas) can be reached if the NLS1 galaxies are relatively young sources with lifetimes not much exceeding 1 Myr. These systems represent sites of strong feedback at NLR scales at work, well below redshift one.

Extreme gaseous outflows in radio-loud narrow-line Seyfert 1 galaxies

Massive black holes in active galaxies are immersed in huge concentrations of late-type stars in the galactic bulges and also early-type massive stars in the nuclear stellar clusters, which are additionally surrounded by quasi-spherical halos on a scale of several kpc that contain from a few hundred up to several thousand globular clusters (GCs). It is expected that significant numbers of red giant stars, massive stars, and also GCs can move through the jet expelled from the central engine of the active galaxy. We consider collisions of stars from the galactic bulge, nuclear cluster, and GCs with the jet plasma. As a result of such collisions, multiple shocks are expected to appear in the jet around these compact objects. Therefore, the plasma in the kpc-scale jet can be significantly disturbed. We show that particles can be accelerated on these shocks up to multi-TeV energies. TeV leptons emit synchrotron radiation, extending up to X-ray energies, and also comptonize radiation produced in a stellar cluster and also the microwave background radiation to TeV gamma-ray energies. We show that such non-thermal radiation is likely to be detectable from the intermediate-scale jets of nearby active galaxies for a reasonable number of stars and GCs immersed within the jet. As an example, we calculate the expected non-thermal emission in X-ray and gamma-ray energies from the nearby radio galaxy Cen A, from which steady gamma-ray emission with a complex spectrum has recently been reported by. Fermi and the HESS Observatories.

Non-thermal radiation from collisions of compact objects with intermediate-scale jets in active galaxies

A new interpretation of the knots in the M87 jet is presented. It is proposed that they are the sites of dense blobs of gas lying within a directed supersonic jet. Jet kinetic energy is dissipated in each knot behind a strong bow shock, where particle acceleration and magnetic field amplification can occur. The momentum flux incident on these obstacles accelerates them in the direction of the jet, and they should cease to radiate efficiently when their velocity approaches that of the jet. The eight known optical knots may be interpreted as either supernova remnants or interstellar clouds. The five outermost knots could be fragments of one such object which became dynamically unstable.

APL and the search for the ultimate prime number program (part 1)

T o illustrate some fundamental differences between array-processing and more traditional, serial languages, lefs look at a ~irly simple problem: h o w do we generate a good palette? The n u m b e r o f colors we can usually deal with in the computer world is about 16 million: this is the n u m b e r o f colors we can represent by 24 bits, a standard for high-definition graphics. However, some c o m m o n bitmap fomnats restrict us to just 256 o f these possibilities by means o f a / , a b e. This is a small subset o f the possible colors we use for a given image. Since this vector o f 256 colors can be indexed by just 8 bits, we can display a wide range o f colors with relatively few bytes, thus keeping the image manageably small. In practice, this restriction can be quite handy, depending on the domain. For instance, if we wish to graphically represent data, 256 distinct colors is sufficiently many to show many values but sufficiently few to n o t overwhelm our ability to make sense o f the distinctions. Also, the .BMP format is conceptually simple to translate to a matrix o f values. This is why I often use it for simple displays of data. For instance, ff I w z n t m display all 256 values, I could enter (in APL) AZZ4-16 1 6 p t 2 5 6. Permbaion to make digital re'herd ~ of all or part of t]-~s work for permmal or clam'oom use is 8rmzted without fee provided that copies are not made or dim-flzzzd f i r pnZ~t or ~.,,~'cJal mivum,ge, mzd that copim Imar this n o t i ~ aml tim full zimaion ml thz firat pag¢. and Blue, the 3 subtracfive primary colors. Typically, each o f the 3 numbers ranges from 0 to 255: the greater the number, the more o f the color present. So, pure red would be (255, 0, 0), pure green is (0, 255, 0) and pure blue is (0, 0, 255). Under this subtra~c/t~ scheme, (255, 255, 255) represents white and (0, 0, O) represents back. We might view these triplets as (x, y, z) coordinates in. 3-space so that the Color Cxtx might look like this: Figure 1: Color Cube …

Good taste in color and soft palettes

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APL and the search for the ultimate prime number program (part 1)

Good taste in color and soft palettes