Global Jet Watch

Abstract:

Cosmic ray (CR) currents through magnetized plasma drive strong instabilities producing amplification of the magnetic field. This amplification helps explain the CR energy spectrum as well as observations of supernova remnants and radio galaxy hotspots. Using magnetohydrodynamic simulations, we study the behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell instability) in the case of CR currents perpendicular and parallel to the initial magnetic field. We demonstrate that extending simulations of the perpendicular case to 3D reveals a different character to the turbulence from that observed in 2D. Despite these differences, in 3D the perpendicular NRH instability still grows exponentially far into the non-linear regime with a similar growth rate to both the 2D perpendicular and 3D parallel situations. We introduce some simple analytical models to elucidate the physical behaviour, using them to demonstrate that the transition to the non-linear regime is governed by the growth of thermal pressure inside dense filaments at the edges of the expanding loops. We discuss our results in the context of supernova remnants and jets in radio galaxies. Our work shows that the NRH instability can amplify magnetic fields to many times their initial value in parallel and perpendicular shocks.

Abstract:

We present new high-resolution, multi-epoch, VLBA radio images of the Galactic microquasar SS 433. We are able to observe plasma knots in the milliarcsecond-scale jets more than 50 days after their launch. This unprecedented baseline in time allows us to determine the bulk launch speed of the radio-emitting plasma during a radio flare, using a new method which we present here, and which is completely independent of optical spectroscopy. We also apply this method to an earlier sequence of 39 short daily VLBA observations, which cover a period in which SS 433 moved from quiescence into a flare. In both datasets we find, for the first time at radio wavebands, clear evidence that the launch speeds of the milliarcsecondscale jets rise as high as 0.32c during flaring episodes. By comparing these images of SS 433 with photometric radio monitoring from the RATAN telescope, we explore further properties of these radio flares.