HESS observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae
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Date
2012Author
Abramowski, A.
Büsching, I.
Casanova, S.
Pekeur, N.W.
Sheidaei, F.
Venter, C.
Vorster, M.
H.E.S.S. Collaboration
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The massive binary system Eta Carinae and the surrounding HII complex, the Carina nebula,
are potential particle acceleration sites from which very high energy (VHE; E ≥ 100 GeV)
γ -ray emission could be expected. This paper presents data collected during VHE γ -ray
observations with the HESS telescope array from 2004 to 2010, which cover a full orbit of
Eta Carinae. In the 33.1-h data set no hint of significant γ -ray emission from Eta Carinae
has been found and an upper limit on the γ -ray flux of 7.7 × 10−13 ph cm−2 s−1 (99 per
cent confidence level) is derived above the energy threshold of 470 GeV. Together with the
detection of high energy (HE; 0.1 ≤ E ≤ 100 GeV) γ -ray emission by the Fermi Large Area
Telescope up to 100 GeV, and assuming a continuation of the average HE spectral index into
the VHE domain, these results imply a cut-off in the γ -ray spectrum between the HE and VHE
γ -ray range. This could be caused either by a cut-off in the accelerated particle distribution
or by severe γ –γ absorption losses in the wind collision region. Furthermore, the search
for extended γ -ray emission from the Carina nebula resulted in an upper limit on the γ -ray
flux of 4.2 × 10−12 ph cm−2 s−1 (99 per cent confidence level). The derived upper limit of
∼23 on the cosmic ray enhancement factor is compared with results found for the old-age
mixed-morphology supernova remnant W28
URI
http://hdl.handle.net/10394/17532http://mnras.oxfordjournals.org/content/424/1/128.full
https://doi.org/10.1111/j.1365-2966.2012.21180.x