X-ray follow-up observations of unidentified VHE gamma-ray sources

TL;DR

This paper reviews the use of X-ray follow-up observations to identify and study the sources of VHE gamma-ray emission in our galaxy, focusing on the detection of signatures of particle acceleration.

Contribution

It discusses the current status and potential of X-ray observations to reveal the nature of unidentified VHE gamma-ray sources and their acceleration mechanisms.

Findings

X-ray signatures can help identify particle acceleration sites.

Spatial offsets complicate source identification.

X-ray observations are effective in tracing high-energy particles.

Abstract

A large fraction of the recently discovered Galactic Very High Energy (VHE) source population remains unidentified to date. VHE gamma-ray emission traces high energy particles in these sources, but for example in case of hadronic processes also the gas density at the emission site. Moreover, the particles have sufficiently long lifetimes to be able to escape from their acceleration sites. Therefore, the gamma-ray sources or at least the areas of maximum surface brightness are in many cases spatially offset from the actual accelerators. A promising way to identify the objects in which the particles are accelerated seems to be to search for emission signatures of the acceleration process (like emission from shock-heated plasma). Also the particles themselves (through primary or secondary synchrotron emission) can be traced in lower wavebands. Those signatures are best visible in the X-ray band, and current X-ray observatories are well suited to conduct such follow-up observations. Some aspects of the current status of these investigations are reviewed.