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Recently, the red giant V723 Mon is reported to have an unseen companion witha mass of $3.04\pm0.06M_{\odot}$, but question remains about whether it is asingle (thus the so-called mass-gap) black hole or an inner binary of two moreordinary compact objects (neutron stars or white dwarfs). In this work, weestimate the X-ray emission by considering the wind-fed accretion from V723 Mononto the compact companion. We analyze three different scenarios of the darkcompanion, i.e., a single black hole, binary neutron stars and binary of aneutron star and a white dwarf. We show that the single black hole is the mostfavored scenario. We also calculate the synchrotron emission from the bow shockcaused by the interaction of the compact companion with the wind. We find thisemission peaks at $\sim$ 0.1-1 GHz, with a flux density $\sim$ 1 mJy, which isexpected to be detected by observations with higher angular resolution in thefuture.

X-ray constraint for the unseen companion of V723 Mon: it is a mass-gap black hole rather than binary neutron stars