Stochastic Acceleration in the Western Hotspot of Pictor A

TL;DR

This paper proposes that stochastic electron acceleration by turbulence explains X-ray features in radio galaxy hotspots better than traditional shock acceleration, demonstrated through observations of Pictor A.

Contribution

It introduces a simple stochastic acceleration model with energy-independent timescales that addresses limitations of shock acceleration in explaining hotspot features.

Findings

Stochastic acceleration explains X-ray features in Pictor A's hotspot.

The model overcomes difficulties faced by shock acceleration models.

Predictions can be tested with future high-energy observations.

Abstract

Chandra's high resolution observations of radio galaxies require a revisit of the relevant electron acceleration processes. Although the diffusive shock particle acceleration model may explain spectra of spatially unresolved sources, it encounters difficulties in explaining the structure and spectral properties of recently discovered Chandra X-ray features in several low-power radio sources. We argue that these observations strongly suggest stochastic electron acceleration by magnetized turbulence, and show that the simplest stochastic particle acceleration model with energy independent acceleration and escape timescales can overcome most of these difficulties. We use the bright core of the western hotspot of Pictor A as an example to demonstrate the model characteristics, which may be tested with high energy observations.