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

Yan Li, Erlin Qiao, Rong-Feng Shen

Recently, the red giant V723 Mon is reported to have an unseen companion with a mass of $3.04\pm 0.06M_{\odot }$, but question remains about whether it is a single (thus the so-calle…