Recently, the red giant V723 Mon is reported to have an unseen companion with a mass of $3.04\pm0.06M_{\odot}$, but question remains about whether it is a single (thus the so-called mass-gap) black hole or an inner binary of two more ordinary compact objects (neutron stars or white dwarfs). In this work, we estimate the X-ray emission by considering the wind-fed accretion from V723 Mon onto the compact companion. We analyze three different scenarios of the dark companion, i.e., a single black hole, binary neutron stars and binary of a neutron star and a white dwarf. We show that the single black hole is the most favored scenario. We also calculate the synchrotron emission from the bow shock caused by the interaction of the compact companion with the wind. We find this emission peaks at $\sim$ 0.1-1 GHz, with a flux density $\sim$ 1 mJy, which is expected to be detected by observations with higher angular resolution in the future.
BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion
Institute of Theoretical Physics, Shanxi University（山西大学理论物理研究所）；State Key Laboratory of Quantum Optics Technologies and Devices, Shanxi University（山西大学量子光学技术与器件国家重点实验室）；Collaborative Innovation Center of Extreme Optics, Shanxi University（山西大学极端光学协同创新中心）；Department of Physics, Taiyuan Normal University（太原师范学院物理系）；Institute of Computational and Applied Physics, Taiyuan Normal University（太原师范学院计算与应用物理研究所）；Shanxi Key Laboratory for Intelligent Optimization Computing and Blockchain Technology（山西省智能优化计算与区块链技术重点实验室）
Weighing Hidden Companions of Compact Object Candidates via Rotational Broadening
Xiamen University（厦门大学）；Quanzhou Normal University（泉州师范学院）；Peking University（北京大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
Response to Comment on "A Non-Interacting Low-Mass Black Hole -- Giant Star Binary System"
van den Heuvel和Tauris认为，如果系统2 MASS J 05215658 +4359220中的红巨星质量为1个太阳质量（M $_\odot$），那么它看不见的伴星可能是由两颗0.9 M的$_\odot$组成的双星，形成一个三重系统。我们认为，现有的数据与质量为$3.2^{+1.0}_{-1.0}$ M $_\odot$的巨星最一致，这意味着$3.3^{+2.8}_{-0.7}$ M $_\odot$的黑洞伴星。
Discovery of a Candidate Black Hole - Giant Star Binary System in the Galactic Field
我们报告的发现，第一个可能的黑洞在一个非相互作用的双星系统与外地红巨星。通过将来自阿帕奇点天文台星系演化实验（APOGEE）的径向速度测量与来自超新星全天空自动巡天（ASAS-SN）的光度变化数据相结合，我们确定了明亮的快速旋转巨星2 MASS J 05215658 +4359220是一个带有巨大的看不见的伴星的双星系统。随后的径向速度测量揭示了一个轨道周期为83天，离心率接近零的系统。这颗巨星的光度变化周期与轨道周期一致，表明恒星黑子和潮汐同步。根据光度、表面重力和温度对这颗巨星的质量和半径的限制，意味着它有一颗质量为$3.3^{+2.8}_{-0.7}$ M $_\odot$的伴星，这意味着它是一颗低质量的黑洞或质量极大的中子星。通过{ \it Gaia}对天体测量双星运动的测量将进一步表征该系统。这一发现证明了像APOGEE这样的大规模光谱测量和像ASAS-SN这样的全天空高节奏光度测量的潜力，以彻底改变我们对紧凑物体质量函数的理解，并测试双星演化和超新星机制的理论。
