A Chandra study of particle acceleration in the multiple hotspots of nearby radio galaxies

TL;DR

This study uses Chandra X-ray observations to investigate particle acceleration in multiple hotspots of nearby radio galaxies, revealing that secondary hotspots can also accelerate particles to high energies, challenging simple shock models.

Contribution

It provides new evidence that secondary hotspots in radio galaxies can be sites of high-energy particle acceleration, contrary to previous assumptions.

Findings

Secondary hotspots are X-ray sources indicating high-energy acceleration.

X-ray structures do not always align with radio or optical peaks.

High-energy particle acceleration sites are more complex than simple shock models.

Abstract

We present Chandra observations of a small sample of nearby classical double radio galaxies which have more than one radio hotspot in at least one of their lobes. The X-ray emission from the hotspots of these comparatively low-power objects is expected to be synchrotron in origin, and therefore to provide information about the locations of high-energy particle acceleration. In some models of the relationship between the jet and hotspot the hotspots that are not the current jet termination point should be detached from the energy supply from the active nucleus and therefore not capable of accelerating particles to high energies. We find that in fact some secondary hotspots are X-ray sources, and thus probably locations for high-energy particle acceleration after the initial jet termination shock. In detail, though, we show that the spatial structures seen in X-ray are not consistent with naive expectations from a simple shock model: the current locations of the acceleration of the highest-energy observable particles in powerful radio galaxies need not be coincident with the peaks of radio or even optical emission.