Discovery of very high energy gamma-ray emission in the W 28 (G6.4-0.1) region, and multiwavelength comparisons

TL;DR

This study reports the discovery of very high energy gamma-ray emission in the W 28 supernova remnant region, highlighting interactions with molecular clouds and multiwavelength observations that reveal complex astrophysical processes.

Contribution

The paper presents new VHE gamma-ray detections in W 28, linking them to molecular cloud interactions and providing multiwavelength analysis that advances understanding of old supernova remnants.

Findings

VHE gamma-ray emission at W 28 boundaries

Interaction with dense molecular clouds confirmed

Multiwavelength data shows complex emission regions

Abstract

H.E.S.S. observations of the old-age (>10^4yr; ~0.5deg diameter) composite supernova remnant (SNR) W 28 reveal very high energy (VHE) gamma-ray emission situated at its northeastern and southern boundaries. The northeastern VHE source (HESS J1801-233) is in an area where W 28 is interacting with a dense molecular cloud, containing OH masers, local radio and X-ray peaks. The southern VHE sources (HESS J1800-240 with components labelled A, B and C) are found in a region occupied by several HII regions, including the ultracompact HII region W 28A2. Our analysis of NANTEN CO data reveals a dense molecular cloud enveloping this southern region, and our reanalysis of EGRET data reveals MeV/GeV emission centred on HESS J1801-233 and the northeastern interaction region.