The very high energy (VHE) γ-ray source HESS J0632+057 has recently been confirmed to be a γ-ray binary. The optical counterpart is the Be star MWC 148, and a compact object of unknown nature orbits it every 321days 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 γ-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no γ-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus, HESS J0632+057 exhibits γ-ray variability on timescales of the order of one to two months possibly linked to the X-ray outburst that takes place about 100days after the periastron passage. Furthermore, our measurements provide for the first time the γ-ray spectrum down to about 140GeV and indicate no turnover of the spectrum at low energies. We compare the properties of HESS J0632+057 with the similar γ-ray binary LS I +61°303 and discuss the possible origin of the multi-wavelength emission of the source. © 2012. The American Astronomical Society. All rights reserved.
- binaries: general
- gamma rays: general
- stars: individual (MWC 148)
- X-rays: binaries
- X-rays: individual (HESS J0632+057)