MAGIC observations of MWC 656, the only known Be/BH system

Abstract

Context. MWC 656 has recently been established as the first observationally detected high-mass X-ray binary system containing a Be star and a black hole (BH). The system has been associated with a gamma-ray flaring event detected by the AGILE satellite in July 2010. Aims. Our aim is to evaluate whether the MWC 656 gamma-ray emission extends to very high energy (VHE > 100 GeV) gamma rays. Methods. We observed MWC 656 with the MAGIC telescopes for ~23 h during two observation periods: between May and June 2012, and in June 2013. During the last period, observations were performed contemporaneously with X-ray (XMM-Newton) and optical (STELLA) instruments. Results. We did not detect the MWC 656 binary system at TeV energies with the MAGIC telescopes in either of the two campaigns. Upper limits (ULs) to the integral flux above 300 GeV have been set, as well as differential ULs at a level of ~5% of the Crab nebula flux. The results obtained from the MAGIC observations do not support persistent emission of VHE gamma rays from this system at a level of 2.4% the Crab flux.