Discovery of extended VHE gamma-ray emission from the asymmetric pulsar wind nebula in MSH 15-52 with HESS

The Supernova Remnant MSH 15-52 has been observed in very high energy (VHE) $\gamma$-rays using the HESS 4-telescope array located in Namibia. A $\gamma$-ray signal is detected at the 25 sigma level during an exposure of 22.1 h live time. The image reveals an elliptically shaped emission region around the pulsar PSR B1509-58, with semi-major axis ~6' in the NW-SE direction and semi-minor axis ~2'. This morphology coincides with the diffuse pulsar wind nebula as observed at X-ray energies by ROSAT. The overall energy spectrum from 280 GeV up to 40 TeV can be fitted by a power law with photon index $\Gamma=2.27\pm0.03_{\textrm {\scriptsize\,stat}}\pm 0.20_{\textrm{\scriptsize\,syst}}$. The detected emission can be plausibly explained by inverse Compton scattering of accelerated relativistic electrons with soft photons.