A search for very high energy γ-ray emission from the starburst galaxy NGC253 with HESS

Abstract

We present the result of 28 h of observations of the nearby starburst galaxy NGC 253 with the HESS detector in 2003. We find no evidence for very high energy y-ray emission from this object. Gamma-ray emission above 400 GeV from NGC 253 had been reported by the CANGAROO collaboration in 2002. From the HESS data we derive upper limits on the flux above 300 GeV of 1.9 × 10 -12 photons cm-2 s-1 for a point-like source and 6.3 × 10-12 photons cm-2 s-1 for a source of radius 0.5° as reported by CANGAROO, both at a confidence level of 99%. These upper limits are inconsistent with the spectrum reported by CANGAROO. The expected very high energy γ-ray emission from this object is discussed in the framework of a galactic wind propagation model. © ESO 2005.