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

TL;DR

This study reports the detection of very high energy gamma-ray emission from HESS J0632+057 during an X-ray outburst, revealing variability linked to the system's orbital phase and providing the first spectrum down to 140 GeV.

Contribution

First detection of VHE gamma-ray emission from HESS J0632+057 during an X-ray outburst, with spectral measurements down to 140 GeV and analysis of variability patterns.

Findings

Gamma-ray emission detected during X-ray outburst

No gamma-ray signal outside outburst periods

Spectrum shows no turnover at low energies

Abstract

The very high energy (VHE) \gamma-ray source HESS J0632+057 has recently been confirmed to be a \gamma-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 \gamma-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no \gamma-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus HESS J0632+057 exhibits \gamma-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 \gamma-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 \gamma-ray binary LS I +61 303, and discuss on the possible origin of the multi-wavelength emission of the source