HESS observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae

HESS Collaboration.

Serie: Trabajos publicados del IAR ; no. 1206

Resumen: The massive binary system Eta Carinae and the surrounding H II complex, the Carina nebula, are potential particle acceleration sites from which very high energy (VHE; E>= 100 GeV) gamma-ray emission could be expected. This paper presents data collected during VHE gamma-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 gamma-ray emission from Eta Carinae has been found and an upper limit on the gamma-ray flux of ? (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) gamma-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 gamma-ray spectrum between the HE and VHE gamma-ray range. This could be caused either by a cut-off in the accelerated particle distribution or by severe gamma-gamma absorption losses in the wind collision region. Furthermore, the search for extended gamma-ray emission from the Carina nebula resulted in an upper limit on the gamma-ray flux of ? (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