Context. 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. Aims. The hydrodynamics of the interaction between a jet and a clumpy wind is studied, focusing on the global wind- and single clump-jet interplay. Methods. We have performed, using the code Ratpenat, three-dimensional numerical simulations of a clumpy wind interacting with a mildly relativistic jet, and of individual clumps penetrating into a jet. Results. 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 ~1037 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. Conclusions. 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.
Several supersonic runaway pulsar wind nebulae (sPWNe) with jet-like extended structures have been recently discovered in X-rays. If these structures are the product of electrons escaping the system ...and diffusing into the surrounding interstellar medium, they can produce a radio halo extending for several arcmins around the source. We model the expected radio emission in this scenario in the Lighthouse Nebula sPWN. We assume a constant particle injection rate during the source lifetime, and isotropic diffusion into the surrounding medium. Our predictions strongly depend on the low- and high-energy cutoffs given in the particle distribution. Our results indicate that extended radio emission can be detected from the Lighthouse Nebula without the need to invoke extreme values for the model parameters. We provide synthetic synchrotron maps that can be used to constrain these results with observations by current highly sensitive radio instruments.
We conducted an observational campaign towards one of the most massive and luminous colliding wind binaries in the Galaxy, HD 93129A, close to its periastron passage in 2018. During this time the ...source was predicted to be in its maximum of high-energy emission. Here we present our data analysis from the X-ray satellites Chandra and NuSTAR and the γ-ray satellite AGILE. High-energy emission coincident with HD 93129A was detected in the X-ray band up to 18 keV, whereas in the γ-ray band only upper limits were obtained. We interpret the derived fluxes using a non-thermal radiative model for the wind-collision region. We establish a conservative upper limit for the fraction of the wind kinetic power that is converted into relativistic electron acceleration, f(NT,e) < 0.02. In addition, we set a lower limit for the magnetic field in the wind-collision region as BWCR > 0.3 G. We also argue a putative interpretation of the emission from which we estimate f(NT,e) ≈ 0.006 and B(WCR) ≈ 0.5 G. We conclude that multi-wavelength, dedicated observing campaigns during carefully selected epochs are a powerful tool for characterising the relativistic particle content and magnetic field intensity in colliding wind binaries.
Context. High-mass microquasars may produce jets that will strongly interact with surrounding stellar winds on binary system spatial scales. Aims. We study the dynamics of the collision between a ...mildly relativistic hydrodynamical jet of supersonic nature and the wind of an OB star. Methods. We performed numerical 3D simulations of jets that cross the stellar wind with the code Ratpenat. Results. The jet head generates a strong shock in the wind, and strong recollimation shocks occur due to the initial overpressure of the jet with its environment. These shocks can accelerate particles up to TeV energies and produce gamma-rays. The recollimation shock also strengthens jet asymmetric Kelvin-Helmholtz instabilities produced in the wind/jet contact discontinuity. This can lead to jet disruption even for jet powers of several times 1036 erg s-1. Conclusions. High-mass microquasar jets likely suffer a strong recollimation shock that can be a site of particle acceleration up to very high energies, but also eventually lead to the disruption of the jet.
Context.
Isolated stellar-mass black holes accrete gas from their surroundings, often at supersonic speeds, and can form outflows that may influence the accreted gas. The latter process, known as ...mechanical feedback, can significantly affect the accretion rate.
Aims.
We use hydrodynamical simulations to assess the impact of mechanical feedback on the accretion rate when the black hole moves supersonically through a uniform medium.
Methods.
We carried out three-dimensional (3D) hydrodynamical simulations of outflows fueled by accretion that interact with a uniform medium, probing scales equivalent to and larger than the accretor gravitational sphere of influence. In the simulations, the accretor is at rest and the medium moves at supersonic speeds. The outflow power is assumed to be proportional to the accretion rate. The simulations were run for different outflow-medium motion angles and velocity ratios. We also investigated the impact of different degrees of outflow collimation, accretor size, and resolution.
Results.
In general, the accretion rate is significantly affected by mechanical feedback. There is a minor reduction in accretion for outflows perpendicular to the medium motion, but the reduction quickly becomes more significant for smaller angles. Moreover, the decrease in accretion becomes greater for smaller medium-to-outflow velocity ratios. On the other hand, the impact of outflow collimation seems moderate. Mechanical feedback is enhanced when the accretor size is reduced. For a population of black holes with random outflow orientations, the average accretion rate drops by (low–high resolution) ∼0.2 − 0.4 and ∼0.1 − 0.2 for medium-to-outflow velocity ratios of 1/20 and 1/100, respectively, when compared to the corresponding cases without outflow.
Conclusions.
Our results strongly indicate that on the considered scales, mechanical feedback can easily reduce the energy available from supersonic accretion by at least a factor of a few. This aspect should be taken into account when studying the mechanical, thermal, and non-thermal output of isolated black holes.
The gamma-ray binary LS I +61 303 is composed of a Be star and a compact companion orbiting in an eccentric orbit. Variable flux modulated with the orbital period of ~26.5 d has been detected from ...radio to very high-energy gamma rays. In addition, the system presents a superorbital variability of the phase and amplitude of the radio outbursts with a period of ~4.6 yr. We present optical photometric observations of LS I +61 303 spanning ~1.5 yr and contemporaneous Hα equivalent width (EWHα) data. The optical photometry shows, for the first time, that the known orbital modulation suffers a positive orbital phase shift and an increase in flux for data obtained 1-yr apart. This behavior is similar to that already known at radio wavelengths, indicating that the optical flux follows the superorbital variability as well. The orbital modulation of the EWHα presents the already known superorbital flux variability but shows, also for the first time, a positive orbital phase shift. In addition, the optical photometry exhibits a lag of ~0.1–0.2 in orbital phase with respect to the EWHα measurements at similar superorbital phases, and presents a lag of ~0.1 and ~0.3 orbital phases with respect noncontemperaneous radio and X-ray outbursts, respectively. The phase shifts detected in the orbital modulation of thermal indicators, such as the optical flux and the EWHα, are in line with the observed behavior for nonthermal indicators, such as X-ray or radio emission. This shows that there is a strong coupling between the thermal and nonthermal emission processes in the gamma-ray binary LS I +61 303. The orbital phase lag between the optical flux and the EWHα is naturally explained considering different emitting regions in the circumstellar disk, whereas the secular evolution might be caused by the presence of a moving one-armed spiral density wave in the disk.
We propose a model to explain the ultra-bright GeV gamma-ray flares observed from the blazar 3C454.3. The model is based on the concept of a relativistic jet interacting with compact gas ...condensations produced when a star (a red giant) crosses the jet close to the central black hole. The study includes an analytical treatment of the evolution of the envelope lost by the star within the jet, and calculations of the related high-energy radiation. The model readily explains the day-long that varies on timescales of hours, GeV gamma-ray flare from 3C454.3, observed during 2010 November on top of a plateau lasting weeks. In the proposed scenario, the plateau state is caused by a strong wind generated by the heating of the stellar atmosphere due to nonthermal particles accelerated at the jet-star interaction region. The flare itself could be produced by a few clouds of matter lost by the red giant after the initial impact of the jet. In the framework of the proposed scenario, the observations constrain the key model parameters of the source, including the mass of the central black hole: M sub(BH) Asymptotically = to 10 super(9) M sub(middot in circle), the total jet power: L sub(j) Asymptotically = to 10 super(48) erg s super(-1), and the Doppler factor of the gamma-ray emitting clouds: delta Asymptotically = to20. Whereas we do not specify the particle acceleration mechanisms, the potential gamma-ray production processes are discussed and compared in the context of the proposed model. We argue that synchrotron radiation of protons has certain advantages compared to other radiation channels of directlyaccelerated electrons. An injected proton distribution is proportional to E super(-1) or harder below the relevant energies would be favored to alleviate the tight energetic constraints and to avoid the violation of the observational low-energy constraints.
Context. The Fermi bubbles are part of a complex region of the Milky Way. This region presents broadband extended non-thermal radiation, apparently coming from a physical structure rooted at the ...Galactic centre and with a partly ordered magnetic field threading it. Aims. We explore the possibility of an explosive origin for the Fermi bubble region to explain its morphology, in particular that of the large-scale magnetic fields, and provide context for the broadband non-thermal radiation. Methods. We performed 3D magnetohydrodynamical simulations of an explosion that occurred a few million years ago that pushed and sheared a surrounding magnetic loop, anchored in the molecular torus around the Galactic centre. Results. Our results can explain the formation of the large-scale magnetic structure in the Fermi bubble region. Consecutive explosive events may match the morphology of the region better. Faster velocities at the top of the shocks than at their sides may explain the hardening with distance from the Galactic plane found in the GeV emission. Conclusions. In the framework of our scenario, we estimate the lifetime of the Fermi bubbles as ≈2 × 106 yr, with a total energy injected in the explosion(s) of ≳1055 ergs. The broadband non-thermal radiation from the region may be explained by leptonic emission, which is more extended in radio and X-rays, and is confined to the Fermi bubbles in gamma rays.
Context.
Jets of active galactic nuclei are potential accelerators of ultra high-energy cosmic rays. Supernovae can occur inside these jets and contribute to cosmic ray acceleration, particularly of ...heavy nuclei, but that contribution has been hardly investigated so far.
Aims.
We carried out a first dedicated exploration of the role of supernovae inside extragalactic jets in the production of ultra high-energy cosmic rays.
Methods.
We characterized the energy budget of supernova-jet interactions, and the maximum possible energies of the particles accelerated in those events, likely dominated by heavy nuclei. This allowed us to assess whether these interactions can be potential acceleration sites of ultra high-energy cosmic rays, or at least of their seeds. For that, we estimated the cosmic ray luminosity for different galaxy types, and compared the injection rate of cosmic ray seeds into the jet with that due to galactic cosmic ray entrainment.
Results.
Since the supernova is fueled for a long time by the luminosity of the jet, the energy of a supernova-jet interaction can be several orders of magnitude greater than that of an isolated supernova. Thus, despite the low rate of supernovae expected to occur in the jet, they could still provide more seeds for accelerating ultra high-energy particles than cosmic ray entrainment from the host galaxy. Moreover, these interactions can create sufficiently efficient accelerators to be a source of cosmic rays with energies ≳10 EeV.
Conclusions.
Supernova-jet interactions can contribute significantly to the production of ultra high-energy cosmic rays, either directly by accelerating these particles themselves or indirectly by providing pre-accelerated seeds.
Context. Strong interactions between jets and stellar winds at binary-system, spatial-scales could occur in high-mass microquasars. Aims. We study here, mainly from a dynamical but also a radiative ...point of view, the collision between a dense stellar wind and a mildly relativistic hydrodynamical jet of supersonic nature. Methods. We have performed numerical two-dimensional simulations of jets, with cylindrical and planar (slab) symmetry, crossing the stellar-wind material. From the results of the simulations, we derive estimates of the particle acceleration efficiency, using first-order, Fermi-acceleration theory, and provide insight into the possible radiative outcomes. Results. We find that, during jet launching, the jet head generates a strong shock in the wind. During and after this process, strong recollimation shocks can occur due to the initial overpressure of the jet with its environment. The conditions in all these shocks are convenient to accelerate particles up to similar to TeV energies, which can lead to leptonic (synchrotron and inverse Compton) and hadronic (proton- proton) radiation. In principle, the cylindrical jet simulations show that the jet is stable, and can escape from the system even at relatively low power. However, when accounting for the wind ram pressure, the jet can be bent and disrupted for power \la 10 super(36) erg s super(-1).
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