Revisiting the Westerlund 2 Field with the H.E.S.S. Telescope Array

TL;DR

This study re-observed the Westerlund 2 region with H.E.S.S., discovering a new VHE gamma-ray source and analyzing the complex origins of gamma-ray emissions, including potential pulsar wind nebulae and molecular cloud interactions.

Contribution

The paper provides new, deeper VHE observations of Westerlund 2, discovering a new gamma-ray source and exploring its possible association with pulsars and molecular clouds.

Findings

Discovery of a new VHE gamma-ray source HESSJ1026-582.

Identification of a pulsar PSR J1028-5819 coincident with the new source.

Complexity in attributing VHE emission to specific objects in the region.

Abstract

Aims. Previous observations with the H.E.S.S. telescope array revealed the existence of extended very-high-energy (VHE; E>100 GeV) {\gamma}-ray emission, HESS J1023-575, coincident with the young stellar cluster Westerlund 2. At the time of discovery, the origin of the observed emission was not unambiguously identified, and follow-up observations have been performed to further investigate the nature of this {\gamma}-ray source. Methods. The Carina region towards the open cluster Westerlund 2 has been re-observed, increasing the total exposure to 45.9 h. The combined dataset includes 33 h of new data and now permits a search for energy-dependent morphology and detailed spectroscopy. Results. A new, hard spectrum VHE {\gamma}-ray source, HESSJ1026-582, was discovered with a statistical significance of 7{\sigma}. It is positionally coincident with the Fermi LAT pulsar PSR J1028-5819. The positional coincidence and radio/{\gamma}-ray characteristics of the LAT pulsar favors a scenario where the TeV emission originates from a pulsar wind nebula. The nature of HESS J1023-575 is discussed in light of the deep H.E.S.S. observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSRJ1022-5746 and giant molecular clouds in the region. Despite the improved VHE dataset, a clear identification of the object responsible for the VHE emission from HESS J1023-575 is not yet possible, and contribution from the nearby high-energy pulsar and/or the open cluster remains a possibility.