Discovery of the two “wings” of the Kookaburra complex in VHE γ-rays with HESS

Abstract

Aims. Search for Very High Energy γ-ray emission in the Kookaburra complex through observations with the HESS array.

Methods: Stereoscopic imaging of Cherenkov light emission of the γ-ray showers in the atmosphere is used for the reconstruction and selection of the events to search for γ-ray signals. Their spectrum is derived by a forward-folding maximum likelihood fit.

Results: Two extended γ-ray sources with an angular (68%) radius of 3.3-3.4′ are discovered at high (>13σ) statistical significance: HESS J1420-607 and HESS J1418-609. They exhibit a flux above 1 TeV of (2.97 ± 0.18stat ± 0.60sys) × 10-12 and (2.17 ± 0.17stat ± 0.43sys) × 10-12 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 HESS sources.

Conclusions: The two new sources confirm the non-thermal nature of at least parts of the two radio wings which overlap with the γ-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 HESS sources. The most likely explanation for the Very High Energy γ-rays discovered by HESS is inverse Compton emission of accelerated electrons on the Cosmic Microwave Background near the two candidate pulsar wind nebulæ, 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.

Astronomy & Astrophysics 456, 245-251 (2006)
ArXiv pre-print

Auxiliary informations

Figure 1

Fits file

Figure 2

H.E.S.S. data points for Figure 2 (solid points – HESS J1420-607)

Mean energy     Flux      Flux Error ( - / + )

  [TeV]    [/TeV cm^2 s] [/TeV cm^2 s]

 0.39    2.63e-11    7.56e-12    7.64e-12 
 0.61    9.13e-12    1.11e-12    1.04e-12 
 0.97    3.38e-12    4.03e-13    4.04e-13 
 1.54    1.46e-12    1.78e-13    1.80e-13 
 2.45    5.91e-13    8.15e-14    8.19e-14 
 3.88    1.97e-13    3.55e-14    3.52e-14 
 6.14    7.09e-14    1.56e-14    1.59e-14 
 9.73    2.54e-14    7.28e-15    7.33e-15 
15.43    6.81e-15    2.99e-15    2.95e-15 
24.45    1.05e-15    7.72e-16    9.56e-16

H.E.S.S. data points for Figure 2 (open points – HESS J1418-609)

Mean energy     Flux      Flux Error ( - / + )

  [TeV]    [/TeV cm^2 s] [/TeV cm^2 s]

 0.39    3.14e-11    9.00e-12    9.16e-12 
 0.61    7.62e-12    1.12e-12    1.08e-12 
 0.97    2.43e-12    3.97e-13    3.86e-13 
 1.54    9.85e-13    1.67e-13    1.69e-13 
 2.45    4.75e-13    8.03e-14    8.25e-14 
 3.88    1.26e-13    3.34e-14    3.34e-14 
 6.14    4.95e-14    1.45e-14    1.51e-14 
 9.73    2.51e-14    7.53e-15    7.65e-15 
15.43    6.37e-15    3.00e-15    2.97e-15

Remarks: Statistical errors only. Systematic error on energy scale estimated at 20%. See paper for details.

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