Abstract
Aims. Search for Very High Energy gamma-ray emission in the Kookaburra complex through observations with the H.E.S.S. array. Methods. Stereoscopic imaging of Cherenkov light emission of the gamma-ray showers in the atmosphere is used for the reconstruction and selection of the events to search for gamma-ray signals. Their spectrum is derived by a forward-folding maximum likelihood fit. Results. Two extended gamma-ray sources with an angular (68%) radius of 3.3-3.4' are discovered at high (>13sigma) statistical significance: HESS J1420-607 and HESS J1418-609. They exhibit a flux above 1 TeV of (2.97+/-0.18stat +/-0.60sys)x10-12 and (2.17+/-0.17stat +/-0.43sys)x10-12 cm-2 s-1, respectively, and similar hard photon indices ~2.2. Multi-wavelength comparisons show spatial coincidence with the wings of the Kookaburra. Two pulsar wind nebulae candidates, K3/PSR J1420-6048 and the Rabbit, lie on the edge of the H.E.S.S. sources. Conclusions. The two new sources confirm the non-thermal nature of at least parts of the two radio wings which overlap with the gamma-ray emission and establish their connection with the two X-ray pulsar wind nebulae candidates. Given the large point spread function of EGRET, the unidentified source(s) 3EG J1420-6038/GeV J1417-6100 could possibly be related to either or both H.E.S.S. sources. The most likely explanation for the Very High Energy gamma-rays discovered by H.E.S.S. is inverse Compton emission of accelerated electrons on the Cosmic Microwave Background near the two candidate pulsar wind nebulae, K3/PSR J1420-6048 and the Rabbit. Two scenarios which could lead to the observed large (~10 pc) offset-nebula type morphologies are briefly discussed.
Highlights
The complex of compact and extended radio/X-ray sources called Kookaburra, after the name of the Australian bird (Roberts et al 1999), spans over about one square degree along the Galactic plane around l = 313.4◦
Given the discrepancy in spatial resolution between γ-ray observations with EGRET and HESS, we indicate the energy flux of 3EG J1420−6038 for both HESS sources
Two extended VHE sources have been discovered in the wings of the Kookaburra complex, HESS J1420−609 and HESS J1418−607
Summary
The complex of compact and extended radio/X-ray sources called Kookaburra, after the name of the Australian bird (Roberts et al 1999), spans over about one square degree along the Galactic plane around l = 313.4◦. It has been extensively studied in the search for counterparts to the unidentified EGRET source Observations of the Kookaburra region with the HESS (High Energy Stereoscopic System) telescopes and the discovery of two Very High Energy (VHE) γ-ray sources coinciding with its wings are reported.
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