Context. MWC 656 is the recently discovered first binary system case composed of a Be-type star and an accreting black hole. Its low X-ray luminosity indicates that the system is in a quiescent X-ray state. Aims. The aim of our investigation is to establish if the MWC 656 system has detectable radio emission and if the radio characteristics are consistent with those of quiescent black hole systems. Methods. We used three archived VLA data sets, one hour each, at 3 GHz and seven new VLA observations, two hours each, at 10 GHz to produce very high sensitivity images, down to $\sim$1$\,\mu$Jy. Results. We detected the source twice in the new observations: in the first VLA run, at periastron passage, with a flux density of 14.2$\,\pm\,$2.9 $\mu$Jy and by combining all together the other six VLA runs, with a flux density of $3.7 \pm 1.4$ $\mu$Jy. The resulting combined map of the archived observations has the sensitivity of $1 \sigma = 6.6\, \mu Jy$ but no radio emission is there detected. Conclusions. The radio and X-ray luminosities agree with the behaviour of accreting binary black holes in the hard and quiescent state. In particular, MWC 656 in the $L_X$, $L_R$ plane occupies the same region as A0620$-$00 and XTE J1118+480, the faintest known black holes up to now.
翻译:MWC 656 是最近首次发现的由Be型恒星和黑洞组成的第一个二进制系统案例。 其低X光光亮度显示, 系统处于可检测的X光状态。 目标。 我们调查的目的是确定 MWC 656 系统是否有可检测的射电排放, 以及无线电特性是否与Qeane黑洞系统相符。 方法。 我们使用三个存档的VLA数据集, 每一个一小时, 3 GHz 和7个新的VLA观测, 2小时, 每两个小时, 10 GHz 制作非常高敏感图像, 降至$1\\\ mu$Jy。 结果。 我们在新观测中两次检测到源: 在第一个VLA系统运行时, 通量为14.2\ pm\, $2. 9\ muJYy, 并且将其他6 VLA 运行量, 通量密度为3. 0. 4 0. 0. 0. 0. 0. 0 美元。 因此, X 图像的合计敏感度为 X 。