The formation mechanism of the W50/SS 433 complex has long been a mystery. We propose a new scenario in which the SS 433 jets themselves form the W50/SS 433 system. We carry out magnetohydrodynamics simulations of the propagation of two side jets using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times; afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology depends strongly on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.

We present the initial results of our MeerKAT L-band observations of Abell 3376. We achieved higher (5″) angular resolution and better (∼4 μ Jy beam⁻¹) sensitivity compared to the previous observations. Our achieved sensitivity is only a factor of 2 larger than the thermal noise of MeerKAT. Astrometric and flux comparison of discrete compact sources in the field between MeerKAT and the Very Large Array (VLA) indicated that our calibration procedures were successful. We detected West and East relics, and radio galaxies, which have been observed in previous works. With minimal missing flux problem in our MeerKAT observations, we derived the spectral indices of the West relic (−1.22 ± 0.05), East relic (−1.33 ± 0.08) and central radio galaxies (−0.94 ± 0.05). The improved images revealed faint, extending radio arcs for relics, and connection between the East relic and radio galaxies. It is probable that (at least some of) the re-accelerated electrons of the East relic are supplied by the jets of the radio galaxies. No significant diffuse radio emission was found in cluster central part, supporting previous works with a much better upper limit of radio flux of <1.8 × 10²³ W Hz⁻¹.

The radio nebula W 50 is a unique object interacting with the jets of the microquasar SS 433. The SS 433/W 50 system is a good target for investigating the energy of cosmic-ray particles accelerated by galactic jets. We report observations of the radio nebula W 50 conducted with the National Science Foundation’s Karl G. Jansky Very Large Array in the L band (1.0–2.0 GHz). We investigate the secular change of W 50 on the basis of the observations in 1984, 1996, and 2017, and find that most of its structures were stable for 33 yr. We revise the upper-limit velocity of the eastern terminal filament by half to 0.023 c, assuming a distance of 5.5 kpc. We also analyze observational data from the Arecibo Observatory 305 m telescope and identify the H i cavity around W 50 in the velocity range 33.77–55.85 km s⁻¹. From this result, we estimate the maximum energy of the cosmic-ray protons accelerated by the jet terminal region to be above 10^15.5 eV. We also use the luminosity of the gamma-rays in the range 0.5–10 GeV to estimate the total energy of accelerated protons below 5.2 × 10⁴⁸ erg.

We present the results of two-temperature magnetohydrodynamic simulations of the propagation of sub-relativistic jets of active galactic nuclei. The dependence of the electron and ion temperature distributions on the fraction of electron heating, f_e, at the shock front is studied for f_e = 0, 0.05, and 0.2. Numerical results indicate that in sub-relativistic, rarefied jets, the jet plasma crossing the terminal shock forms a hot, two-temperature plasma in which the ion temperature is higher than the electron temperature. The two-temperature plasma expands and forms a backflow referred to as a cocoon, in which the ion temperature remains higher than the electron temperature for longer than 100 Myr. Electrons in the cocoon are continuously heated by ions through Coulomb collisions, and the electron temperature thus remains at T_e > 10⁹ K in the cocoon. X-ray emissions from the cocoon are weak because the electron number density is low. Meanwhile, X-rays are emitted from the shocked intracluster medium (ICM) surrounding the cocoon. Mixing of the jet plasma and the shocked ICM through the Kelvin–Helmholtz instability at the interface enhances X-ray emissions around the contact discontinuity between the cocoon and shocked ICM.

To demonstrate the magnetic energy dissipation via relativistic shocks, we carry out spherically symmetrical one-dimensional special relativistic magnetohydrodynamic simulations of highly magnetized outflows with an adaptive mesh refinement method. We first investigate the details of the dynamical energy dissipation via interaction between a single ejecta and an external medium. The energy dissipation time-scales, which affect the early behaviour of the afterglow emission in gamma-ray bursts, are estimated for a wide range of magnetization. In addition, we demonstrate the internal shock dissipation in multiple interactions between magnetically dominated relativistic ejecta and kinetically dominated non-relativistic winds. Our numerical results show that ∼10 per cent of the magnetic energy in the ejecta can be converted into the thermal energy of the relativistic and low-magnetized outflows via shocks in the rarefaction waves or the winds. Such hot and less magnetized outflows are relevant for observed non-thermal emissions in blazars or gamma-ray bursts.