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

TL;DR

This study used the MAGIC telescopes to observe the Be/BH system MWC 656 in search of very high energy gamma-ray emission, but no such emission was detected, setting upper limits on its flux.

Contribution

First observational attempt to detect VHE gamma rays from MWC 656, establishing upper limits and constraining models of gamma-ray emission in Be/BH systems.

Findings

No detection of TeV gamma rays from MWC 656.

Upper limits set at 5% of Crab flux.

Results do not support persistent VHE emission.

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 if the MWC 656 gamma-ray emission extends to very high energy (VHE > 100 GeV) gamma rays. Methods. We have observed MWC 656 with the MAGIC telescopes for $\sim$23 hours during two observation periods: between May and June 2012 and June 2013. During the last period, observations were performed contemporaneously with X-ray (XMM-Newton) and optical (STELLA) instruments. Results: We have not detected the MWC 656 binary system at TeV energies with the MAGIC Telescopes in either of the two campaigns carried out. Upper limits (ULs) to the integral flux above 300 GeV have been set, as well as differential ULs at a level of $\sim$5% of the Crab Nebula flux. The results obtained from the MAGIC observations do not support persistent emission of very high energy gamma rays from this system at a level of 2.4% the Crab flux.