Detection of VHE ��-rays from HESS J0632+057 during the 2011 February X-ray outburst with the MAGIC Telescopes

The very high energy (VHE) ��-ray source HESS J0632+057 has recently been confirmed to be a ��-ray binary. The optical counterpart is the Be star MWC 148, and a compact object of unknown nature orbits it every ~321 d with a high eccentricity of ~0.8. We monitored HESS J0632+057 with the stereoscopic MAGIC telescopes from 2010 October to 2011 March and detected significant VHE ��-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no ��-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus HESS J0632+057 exhibits ��-ray variability on timescales of the order of one to two months possibly linked to the X-ray outburst that takes place about 100 days after the periastron passage. Furthermore our measurements provide for the first time the ��-ray spectrum down to about 140 GeV and indicate no turnover of the spectrum at low energies. We compare the properties of HESS J0632+057 with the similar ��-ray binary LS I +61 303, and discuss on the possible origin of the multi-wavelength emission of the source
6 pages and 3 figures, submitted, corresponding authors T. Jogler and P. Munar-Adrover